Local superfusion modifies the inward rectifying potassium conductance of isolated retinal horizontal cells

1988 ◽  
Vol 60 (4) ◽  
pp. 1322-1332 ◽  
Author(s):  
I. Perlman ◽  
A. G. Knapp ◽  
J. E. Dowling
Keyword(s):  
White Perch ◽  
Reversal Potential ◽  
Ringer Solution ◽  
Inward Rectifier ◽  
Horizontal Cells ◽  
Equilibrium Potential ◽  
Steady State Current ◽  
Conductance Increase ◽  
Local Superfusion ◽  
Drug Free

1. Horizontal cells were enzymatically and mechanically dissociated from the white perch (Roccus americana) retina and voltage clamped using patch electrodes. Steady-state current-voltage (I-V) relationships of solitary horizontal cells were determined by changing the membrane potential in a rampwise fashion. 2. The I-V curve of cells bathed in normal Ringer solution exhibited a large conductance increase at negative membrane potentials. This conductance activated near the K+ equilibrium potential, had no clear reversal potential, was enhanced by raising the extracellular concentration of K+, and was suppressed by external Cs+. These properties identify the conductance as the inward (anomalous) rectifier. 3. Continuous superfusion of the cells' local environment with drug-free Ringer reduced the magnitude of the inward rectifier current and shifted its activation point to more negative potentials. This effect developed over approximately 30 s, lasted as long as superfusion continued and was reversible upon cessation of superfusion. 4. Pressure ejection of drug-free Ringer solution onto cells bathed in the identical solution also reduced the magnitude of the inward rectifier current, although the effects were more rapid and more transient than those exerted by superfusion. Pressure ejection had little effect when cells were simultaneously superfused with Ringer, suggesting a common mode of action on the inward rectifier. 5. In the absence of superfusion, pressure ejection of Ringer containing 200 microM L-glutamate had a biphasic effect on membrane conductance. At potentials above -60 mV, glutamate caused a conductance increase with a reversal potential near +10 mV. At potentials below -60 mV, glutamate caused a conductance decrease whose reversal potential could not reliably be determined. The latter effect was similar to the suppression of the inward rectifier by application of Ringer alone, suggesting that it may represent an artifact of pressure ejection rather than a direct effect of glutamate. 6. In support of this interpretation, we found that pressure ejection of glutamate in the presence of external Cs+ (which blocks the inward rectifier) or during local superfusion with Ringer (which prevents attenuation of the inward rectifier by pressure ejection) did not cause a conductance decrease at negative potentials. Under these conditions, glutamate caused primarily a conductance increase with a reversal potential near +10 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

Whole cell current analyses of pancreatic acinar AR42J cells. I. Voltage- and Ca(2+)-activated currents

1991 ◽  
Vol 260 (5) ◽  
pp. C934-C948 ◽  
Author(s):  
K. Kusano ◽  
H. Gainer
Keyword(s):  
Reversal Potential ◽  
Outward Current ◽  
Pancreatic Acinar Cells ◽  
Equilibrium Potential ◽  
Channel Blockers ◽  
Whole Cell ◽  
Inward Current ◽  
Tail Current ◽  
Ar42j Cells ◽  
Conductance Increase

Voltage- and Ca(2+)-activated whole cell currents were studied in AR42J cells, a clonal cell line derived from rat pancreatic acinar cells, using a patch electrode voltage-clamp technique. Four kinds of ionic currents were identified by their ionic dependencies, pharmacological properties, and kinetic parameters: 1) an outward current flow due mainly to a voltage-dependent K(+)-conductance increase, 2) an initial transient inward current due to an Na(+)-conductance increase, 3) transient and long-duration inward current due to a Ca(2+)-conductance increase, and 4) a slowly activating inward current that persists over the duration of the depolarizing pulse and deactivates slowly upon repolarization, producing a slow inward tail current. The slow inward tail current was particularly robust and was interpreted as due to a Ca(2+)-activated Cl(-)-conductance increase, since 1) the generation of this current was blocked by removing the extracellular Ca2+, applying Ca(2+)-channel blockers (Cd2+, nifedipine), or by lowering the intracellular Ca2+ concentration [( Ca2+]i) with EGTA; and 2) the reversal potential (Erev) of the slow inward tail current was close to 0 mV in the control condition (152 mM [Cl-]o/154 mM [Cl-]i), and changes of the [Cl-]o/[Cl )i ratio shifted the Erev toward the predicted Cl- equilibrium potential.

Effects of sevoflurane on inward rectifier K+ current in guinea pig ventricular cardiomyocytes

1997 ◽  
Vol 273 (1) ◽  
pp. H324-H332 ◽  
Author(s):  
A. Stadnicka ◽  
Z. J. Bosnjak ◽  
J. P. Kampine ◽  
W. M. Kwok
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Outward Current ◽  
Inward Rectifier ◽  
Equilibrium Potential ◽  
Ventricular Cardiomyocytes ◽  
Steady State Current ◽  
Voltage Dependent ◽  
Current Activation ◽  
Extracellular Side

The effects of sevoflurane on the inward rectifier potassium current (IKIR) were examined in guinea pig ventricular cardiomyocytes using the whole cell patch-clamp methodology. Sevoflurane had a unique dual effect on the steady-state current amplitude, producing a reversible, concentration- and voltage-dependent block of the inward current at potentials negative to the potassium equilibrium potential (EK) but enhancing the outward current positive to EK. Accordingly, the steady-state conductance negative to EK was reduced by sevoflurane, but conductance positive to EK was increased. The chord conductance-voltage relationship showed depolarizing shifts at 0.7, 1.3, and 1.6 mM sevoflurane. When the myocytes were dialyzed with 10 mM Mg2+, but not with 1.0 mM Mg2+, sevoflurane further slowed current activation kinetics. With 10 mM intracellular Mg2+, the outward current enhancement by sevoflurane and the associated shifts in half-activation potential were abolished. Polyamines abolished all effects of sevoflurane on IKIR. With the use of the Woodhull model for voltage-dependent block, we determined the sevoflurane interaction site with the inward rectifier potassium channel to be at an electrical distance of 0.2 from the extracellular side.

On bipolar cell responses in the teleost retina are generated by two distinct mechanisms

1996 ◽  
Vol 76 (6) ◽  
pp. 3842-3849 ◽  
Author(s):  
G. B. Grant ◽  
J. E. Dowling
Keyword(s):  
Lucifer Yellow ◽  
Reversal Potential ◽  
Chloride Ions ◽  
Bipolar Cells ◽  
Equilibrium Potential ◽  
Perforated Patch ◽  
Cell Responses ◽  
Patch Pipette ◽  
Teleost Retina ◽  
Local Superfusion

1. ON Bipolar cells were recorded in slices obtained from hybrid bass retinas. Cells were identified as bipolar cells by position in the slice, by characteristic voltage- and ligand-gated currents, and by filling with the fluorescent dye Lucifer yellow. Cells were recorded with the use of either whole cell or perforated-patch techniques. Standard electrophysiological protocols were used. Drugs were applied by puffing and by local superfusion. 2. Application of exogenous glutamate to ON bipolar cells generated two characteristic responses. One effect of glutamate was to open a conductance with a reversal potential close to the chloride equilibrium potential. The other effect of glutamate was to close a conductance with a reversal potential near 0 mV. These two effects of glutamate on ON bipolar cells match the effects of light described previously with the use of intracellular recordings. Thus the effects of glutamate that we report here appear to underlie the rod and cone inputs to these cells. 3. Many of the ON bipolar cells recorded demonstrated both classes of responses to glutamate. To isolate the two responses, 500 microM glutamate was first applied, and then glutamate in the presence of 5 microM 2-amino-4-phosphonobutyric acid (APB). APB specifically blocks the effects of glutamate on the putative roddriven glutamate receptor (the glutamate-elicited conductance decrease), allowing us to study in isolation the effects of glutamate on the cone component, the glutamate-activated chloride current (IGlu). 4. By isolating IGlu as described above, and taking advantage of the fact that amphotericin-perforated-patch recordings limit the diffusion of chloride ions between the patch pipette and the cell body, we found the physiological reversal potential of IGlu to be -58.9 +/- 7.7 (SD) mV. 5. Both the putative rod- and cone-mediated glutamatergic inputs to these bipolar cells could be activated by driving the photoreceptors with puffs of potassium. The currents recorded with this technique were very similar to those seen with direct application of glutamate.

The excitatory and inhibitory amino acid receptors on horizontal cells isolated from the white perch retina

1993 ◽  
Vol 70 (1) ◽  
pp. 8-19 ◽  
Author(s):  
Z. J. Zhou ◽  
G. L. Fain ◽  
J. E. Dowling
Keyword(s):  
Amino Acid ◽  
White Perch ◽  
Glycine Receptor ◽  
Horizontal Cells ◽  
Hill Coefficient ◽  
Equilibrium Potential ◽  
Homogeneous Distribution ◽  
Response Analysis ◽  
Bathing Solution ◽  
Whole Cell

1. The distribution and the properties of receptors to the inhibitory amino acid glycine (GLY) and the excitatory amino acid glutamate (GLU) and its analogues kainate (KA), quisqualate (QUIS), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and N-methyl-D-aspartate (NMDA), were studied with whole-cell and outside-out patch-clamp techniques on all four types of horizontal cells isolated from the retina of white perch. 2. Glycine at concentrations above 30 microM evoked whole-cell current responses from two types of horizontal cells (H2 and H4). The other two types of horizontal cells (H1 and H3) were unresponsive to GLY (30 microM-3 mM). 3. Responses elicited by GLY from H2 and H4 cells were similar, consisting of inward currents that desensitized with a half-decay time of 0.5-2 s at glycine concentrations between 100 and 500 microM. GLY-activated currents were inhibited by the glycine receptor antagonist strychnine (STRYCH). Current responses evoked by GLY reversed at the Cl- equilibrium potential. 4. Dose-response analysis of peak currents induced by GLY revealed a Hill coefficient of 2.0 +/- 0.1 (mean +/- SD, n = 3) and an median effective concentration (EC50) of 85 +/- 2 microM (n = 3). 5. Single glycine receptor channels recorded from outside-out patches had a main-state conductance of 47 +/- 4 pS (n = 3). 6. Every type of horizontal cell from the white perch responded to GLU, KA, QUIS, and AMPA but none responded to exogenously applied NMDA (200 microM) or NMDA (200 microM) + GLY (1 microM) in a Mg+2-free bathing solution. 7. The ratio of the amplitude of responses to GLU, KA, QUIS, and AMPA remained nearly constant among all the horizontal cells tested, suggesting there might be only a single population of non-NMDA receptors on these cells. 8. QUIS and KA both elicited responses from the horizontal cells. When applied together with KA, QUIS competitively antagonized the responses of horizontal cells to KA. 9. The results demonstrated the existence of an inhomogeneous distribution of strychnine-sensitive glycine receptors and a homogeneous distribution of non-NMDA type glutamate receptors among the four types of white perch horizontal cells.

Nitric Oxide Activates Leak K+ Currents in the Presumed Cholinergic Neuron of Basal Forebrain

2007 ◽  
Vol 98 (6) ◽  
pp. 3397-3410 ◽  
Author(s):  
Youngnam Kang ◽  
Yoshie Dempo ◽  
Atsuko Ohashi ◽  
Mitsuru Saito ◽  
Hiroki Toyoda ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Basal Forebrain ◽  
Reversal Potential ◽  
Soluble Guanylyl Cyclase ◽  
Outward Current ◽  
Pump Current ◽  
Atp Depletion ◽  
Equilibrium Potential ◽  
No Donor ◽  
Bath Application

Learning and memory are critically dependent on basal forebrain cholinergic (BFC) neuron excitability, which is modulated profoundly by leak K+ channels. Many neuromodulators closing leak K+ channels have been reported, whereas their endogenous opener remained unknown. We here demonstrate that nitric oxide (NO) can be the endogenous opener of leak K+ channels in the presumed BFC neurons. Bath application of 1 mM S-nitroso- N-acetylpenicillamine (SNAP), an NO donor, induced a long-lasting hyperpolarization, which was often interrupted by a transient depolarization. Soluble guanylyl cyclase inhibitors prevented SNAP from inducing hyperpolarization but allowed SNAP to cause depolarization, whereas bath application of 0.2 mM 8-bromoguanosine-3′,5′-cyclomonophosphate (8-Br-cGMP) induced a similar long-lasting hyperpolarization alone. These observations indicate that the SNAP-induced hyperpolarization and depolarization are mediated by the cGMP-dependent and -independent processes, respectively. When examined with the ramp command pulse applied at –70 mV under the voltage-clamp condition, 8-Br-cGMP application induced the outward current that reversed at K+ equilibrium potential ( EK) and displayed Goldman-Hodgkin-Katz rectification, indicating the involvement of voltage-independent K+ current. By contrast, SNAP application in the presumed BFC neurons either dialyzed with the GTP-free internal solution or in the presence of 10 μM Rp-8-bromo-β-phenyl-1,N2-ethenoguanosine 3′,5′-cyclic monophosphorothioate sodium salt, a protein kinase G (PKG) inhibitor, induced the inward current that reversed at potentials much more negative than EK and close to the reversal potential of Na+-K+ pump current. These observations strongly suggest that NO activates leak K+ channels through cGMP-PKG-dependent pathway to markedly decrease the excitability in BFC neurons, while NO simultaneously causes depolarization by the inhibition of Na+-K+ pump through ATP depletion.

Neuronal Sodium Leak Channel Is Responsible for the Detection of Sodium in the Rat Median Preoptic Nucleus

2011 ◽  
Vol 105 (2) ◽  
pp. 650-660 ◽  
Author(s):  
Christina Tremblay ◽  
Emmanuelle Berret ◽  
Mélaine Henry ◽  
Benjamin Nehmé ◽  
Louis Nadeau ◽  
...  
Keyword(s):  
Close Contact ◽  
Critical Role ◽  
Reversal Potential ◽  
Outward Current ◽  
The Body ◽  
Equilibrium Potential ◽  
Preoptic Nucleus ◽  
Leak Channel ◽  
Median Preoptic Nucleus ◽  
Electrophysiological Recordings

Sodium (Na+) ions are of primary importance for hydromineral and cardiovascular homeostasis, and the level of Na+ in the body fluid compartments [plasma and cerebrospinal fluid (CSF)] is precisely monitored in the hypothalamus. Glial cells seem to play a critical role in the mechanism of Na+ detection. However, the precise role of neurons in the detection of extracellular Na+ concentration ([Na+]out) remains unclear. Here we demonstrate that neurons of the median preoptic nucleus (MnPO), a structure in close contact with the CSF, are specific Na+ sensors. Electrophysiological recordings were performed on dissociated rat MnPO neurons under isotonic [Na+] (100 mM NaCl) with local application of hypernatriuric (150, 180 mM NaCl) or hyponatriuric (50 mM NaCl) external solution. The hyper- and hyponatriuric conditions triggered an in- and an outward current, respectively. The reversal potential of the current matched the equilibrium potential of Na+, indicating that a change in [Na+]out modified the influx of Na+ in the MnPO neurons. The conductance of the Na+ current was not affected by either the membrane potential or the [Na+]out. Moreover, the channel was highly selective for lithium over guanidinium. Together, these data identified the channel as a Na+ leak channel. A high correlation between the electrophysiological recordings and immunofluorescent labeling for the NaX channel in dissociated MnPO neurons strongly supports this channel as a candidate for the Na+ leak channel responsible for the Na+-sensing ability of rat MnPO neurons. The absence of NaX labeling and of a specific current evoked by a change in [Na+]out in mouse MnPO neurons suggests species specificity in the hypothalamus structures participating in central Na+ detection.

Cholecystokinin-gated currents in neurons of the rat solitary complex in vitro

1993 ◽  
Vol 70 (6) ◽  
pp. 2584-2595 ◽  
Author(s):  
P. Branchereau ◽  
J. Champagnat ◽  
M. Denavit-Saubie
Keyword(s):  
Voltage Clamp ◽  
Potassium Current ◽  
Reversal Potential ◽  
Input Resistance ◽  
Calcium Currents ◽  
Equilibrium Potential ◽  
Potassium Ions ◽  
Nernst Equation ◽  
Membrane Hyperpolarization ◽  
Cckb Receptor

1. Ionic conductances controlled by type A and type B cholecystokinin (CCK) receptors were studied in neurons of the rat nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMNV), using intracellular and whole-cell patch clamp recordings in current or voltage clamp configuration during bath application of agonists (CCK8, CCK4, BC 264) and antagonists. 2. CCKA receptor-related inhibition was associated with a membrane hyperpolarization and a decrease in input resistance that developed 2-6 min after the arrival of drug into the extracellular medium. These effects were induced by 5 nM CCK8 but not BC 264 and they were blocked by the CCKA antagonist, L-364,718, but not by the CCKB antagonist, L-365,260. 3. CCKA receptor-related inhibition was generated by a potassium current that reversed at a reversal potential E(rev) of -73 +/- 1 (mean +/- SE) mV with bathing potassium concentration [K+]o = 6 mM and at -88 +/- 1 with [K+]o = 3 mM, in agreement with the Nernst equation for potassium ions. 4. CCKB receptor-related excitation was associated with a membrane depolarization and an increase of the input resistance induced by the following agonists at threshold concentrations: CCK8 (0.2 nM) > or = BC 264 (0.4 nM) > CCK4 (10.9 nM). The increase of input resistance was abolished by L-365,260 and was maintained after blockade of the CCKA current by L-364,718. 5. CCKB receptor-related excitation, in the neurons (30% of cases) in which clear response reversal was observed, appeared to be generated by a decrease of a potassium conductance. Responses showed a reversal potential E(rev) of -68 +/- 4 mV with [K+]o = 6 mM and -89 +/- 1 mV with [K+]o = 3 mM, verifying predictions from the Nernst equation applied to potassium ions. However, in 70% of cases, clear reversal was not observed at membrane potentials negative to the theoretical potassium equilibrium potential EK. 6. In voltage clamp studies, CCK8 induced a 181 +/- 17 pA inward current associated with a 26 +/- 4% decrease in the instantaneous current (I(ins)) generated by hyperpolarizing voltage steps. This effect on I(ins) was demonstrated in the absence of effects on the outward noninactivating potassium current (IM) and on the inward noninactivating cationic current (IQ). 7. CCKB receptor-mediated excitation was not suppressed by cobalt, a blocker of calcium currents, and was not associated with a change of the calcium-dependent potassium current (IK(Ca)).(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of synaptically mediated fast and slow inhibitory processes in piriform cortex in an in vitro slice preparation

1988 ◽  
Vol 59 (5) ◽  
pp. 1352-1376 ◽  
Author(s):  
G. F. Tseng ◽  
L. B. Haberly
Keyword(s):  
Membrane Potential ◽  
Piriform Cortex ◽  
Reversal Potential ◽  
Pyramidal Cells ◽  
Membrane Depolarization ◽  
Resting Membrane Potential ◽  
Excitatory Postsynaptic Potential ◽  
Pentobarbital Sodium ◽  
Postsynaptic Potential ◽  
Conductance Increase

1. Intracellular recordings were obtained from anatomically verified layer II pyramidal cells in slices from rat piriform cortex cut perpendicular to the surface. 2. Responses to afferent and association fiber stimulation at resting membrane potential consisted of a depolarizing potential followed by a late hyperpolarizing potential (LHP). Membrane polarization by current injection revealed two components in the depolarizing potential: an initial excitatory postsynaptic potential (EPSP) followed at brief latency by an inhibitory postsynaptic potential (IPSP) that inverted with membrane depolarization and truncated the duration of the EPSP. 3. The early IPSP displayed the following characteristics suggesting mediation by gamma-aminobutyric acid (GABA) receptors linked to Cl- channels: associated conductance increase, sensitivity to increases in internal Cl- concentration, blockage by picrotoxin and bicuculline, and potentiation by pentobarbital sodium. The reversal potential was in the depolarizing direction with respect to resting membrane potential so that the inhibitory effect was exclusively via current shunting. 4. The LHP had an associated conductance increase and a reversal potential of -90 mV in normal bathing medium that shifted according to Nernst predictions for a K+ potential with changes in external K+ over the range 4.5-8 mM indicating mediation by the opening of K+ channels and ruling out an electrogenic pump origin. 5. Lack of effect of bath-applied 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) or internally applied ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) on the LHP and failure of high amplitude, direct membrane depolarization to evoke a comparable potential, argue against endogenous mediation of the LHP by a Ca2+ activated K+ conductance [gK(Ca)]. However, an apparent endogenously mediated gK(Ca) with a duration much greater than the LHP was observed in a low percent of layer II pyramidal cells. Lack of effect of 8-Br-cAMP also indicates a lack of dependence of the LHP on cAMP. 6. Other characteristics of the LHP that were demonstrated include: a lack of blockage by GABAA receptor antagonists, a probable voltage sensitivity (decrease in amplitude in the depolarizing direction), and an apparent brief onset latency (less than 10 ms) when the early IPSP was blocked by picrotoxin. The LHP was unaffected by pentobarbital sodium when the early IPSP was blocked by picrotoxin. 7. Both the LHP and early IPSP were blocked by low Ca2+/high Mg2+, consistent with disynaptic mediation.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in membrane currents of hippocampal neurons evoked by brief anoxia

1989 ◽  
Vol 62 (1) ◽  
pp. 15-30 ◽  
Author(s):  
K. Krnjevic ◽  
J. Leblond
Keyword(s):  
Hippocampal Neurons ◽  
Hippocampal Slices ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Currents ◽  
Sprague Dawley ◽  
Persistent Currents ◽  
Inward Currents ◽  
The Difference ◽  
Conductance Increase

1. Effects of anoxia (2-4 min of 95% N2-5% CO2) on membrane currents of CA1 neurons were studied by single-electrode voltage clamp in hippocampal slices (from Sprague-Dawley rats) kept in an interface-type chamber at 33.5 degree. 2. When recording with KCl electrodes at a holding potential (VH) near-70 mV, anoxia evoked a slow outward current [0.18 +/- 0.06 (SE) nA], accompanied by a conductance increase ( + 46 +/- 20%, mean +/- SE). The difference current evoked by N2 had a reversal potential near-100 mV. It was much smaller in presence of 2-4 mM extracellular Cs, and any remaining outward current was abolished by 10 mM tetraethylammonium (TEA). Only inward currents were observed when recording with CsCl electrodes. 3. Inward relaxations evoked by large hyperpolarizing pulses from VH less than or equal to - 70 mV (Q-type) were not significantly depressed by anoxia (-1.5 +/- 6.0%). 4. Some voltage-dependent outward currents (evoked by 200-ms depolarizing pulses) were depressed during anoxia: 1) a fast-inactivating (A-like) current, obtained at VH less than or equal to -70 mV and suppressed by 200 microM 4-AP, was reduced by 25.6 +/- 7.3% (n = 5); 2) a slower, noninactivating (C-like) current, suppressed by TEA, was reduced by 52 +/- 7.2% (n = 16). Neither of these currents (1 or 2) was observed when recording with 2- to 3-M CsCl electrodes; and 3) small (M-like) inward relaxations, observed at VH approximately -40 mV 5. Net inward currents could be evoked after blockage of GK with 10 mM TEA when recording with KCl electrodes or by recording with CsCl electrodes. At VH less than or equal to -70 mV, large, transient, and incompletely controlled currents were evoked by depolarizing pulses; at VH less than or equal to -50 mV, smaller and more persistent currents were evoked by depolarizing pulses (L-like), and transient currents (T-like?) were seen immediately after hyperpolarizing pulses. 6.L-type currents (at VH less than or equal to -50 mV) were nearly abolished after 1-2 min anoxia (by approximately 90%). This was equally true of the currents evoked by constant pulses or peak currents in I-V plots. After reoxygenation, recovery was biphasic, with a quick early phase (to 50-80% in 2 min) and then a much slower one (to 60-90% by 10-15 min).(ABSTRACT TRUNCATED AT 400 WORDS)

Ca2+-activated Cl− current in cultured myenteric neurons from murine proximal colon

2003 ◽  
Vol 284 (4) ◽  
pp. C839-C847 ◽  
Author(s):  
Sok Han Kang ◽  
Pieter Vanden Berghe ◽  
Terence K. Smith
Keyword(s):  
Membrane Potential ◽  
Channel Blocker ◽  
Reversal Potential ◽  
Outward Current ◽  
Proximal Colon ◽  
Time Dependent ◽  
Equilibrium Potential ◽  
Resting Membrane Potential ◽  
Myenteric Neurons ◽  
Whole Cell Patch Clamp

Whole cell patch-clamp recordings were made from cultured myenteric neurons taken from murine proximal colon. The micropipette contained Cs+ to remove K+ currents. Depolarization elicited a slowly activating time-dependent outward current ( I tdo), whereas repolarization was followed by a slowly deactivating tail current ( I tail). I tdo and I tail were present in ∼70% of neurons. We identified these currents as Cl− currents ( I Cl), because changing the transmembrane Cl− gradient altered the measured reversal potential ( E rev) of both I tdo and I tail with that for I tailshifted close to the calculated Cl− equilibrium potential ( E Cl). I Cl are Ca2+-activated Cl− current [ I Cl(Ca)] because they were Ca2+dependent. E Cl, which was measured from the E rev of I Cl(Ca) using a gramicidin perforated patch, was −33 mV. This value is more positive than the resting membrane potential (−56.3 ± 2.7 mV), suggesting myenteric neurons accumulate intracellular Cl−. ω-Conotoxin GIVA [0.3 μM; N-type Ca2+ channel blocker] and niflumic acid [10 μM; known I Cl(Ca) blocker], decreased the I Cl(Ca). In conclusion, these neurons have I Cl(Ca) that are activated by Ca2+entry through N-type Ca2+ channels. These currents likely regulate postspike frequency adaptation.

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