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.

Direct Excitation of Mitral Cells Via Activation of α1-Noradrenergic Receptors in Rat Olfactory Bulb Slices

2001 ◽  
Vol 86 (5) ◽  
pp. 2173-2182 ◽  
Author(s):  
Abdallah Hayar ◽  
Phillip M. Heyward ◽  
Thomas Heinbockel ◽  
Michael T. Shipley ◽  
Matthew Ennis
Keyword(s):  
Olfactory Bulb ◽  
Locus Coeruleus ◽  
Equilibrium Potential ◽  
Channel Blockers ◽  
Mitral Cells ◽  
Patch Clamp Recording ◽  
Whole Cell ◽  
Inward Current

The main olfactory bulb receives a significant modulatory noradrenergic input from the locus coeruleus. Previous in vivo and in vitro studies showed that norepinephrine (NE) inputs increase the sensitivity of mitral cells to weak olfactory inputs. The cellular basis for this action of NE is not understood. The goal of this study was to investigate the effect of NE and noradrenergic agonists on the excitability of mitral cells, the main output cells of the olfactory bulb, using whole cell patch-clamp recording in vitro. The noradrenergic agonists, phenylephrine (PE, 10 μM), isoproterenol (Isop, 10 μM), and clonidine (3 μM), were used to test for the functional presence of α1-, β-, and α2-receptors, respectively, on mitral cells. None of these agonists affected olfactory nerve (ON)–evoked field potentials recorded in the glomerular layer, or ON-evoked postsynaptic currents recorded in mitral cells. In whole cell voltage-clamp recordings, NE (30 μM) induced an inward current (54 ± 7 pA, n= 16) with an EC50 of 4.7 μM. Both PE and Isop also produced inward currents (22 ± 4 pA, n = 19, and 29 ± 9 pA, n = 8, respectively), while clonidine produced no effect ( n = 6). In the presence of TTX (1 μM), and blockers of excitatory and inhibitory fast synaptic transmission [gabazine 5 μM, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) 10 μM, and (±)-2-amino-5-phosphonopentanoic acid (APV) 50 μM], the inward current induced by PE persisted (EC50 = 9 μM), whereas that of Isop was absent. The effect of PE was also observed in the presence of the Ca2+ channel blockers, cadmium (100 μM) and nickel (100 μM). The inward current caused by PE was blocked when the interior of the cell was perfused with the nonhydrolyzable GDP analogue, GDPβS, indicating that the α1 effect is mediated by G-protein coupling. The current-voltage relationship in the absence and presence of PE indicated that the current induced by PE decreased near the equilibrium potential for potassium ions. In current-clamp recordings from bistable mitral cells, PE shifted the membrane potential from the downstate (−52 mV) toward the upstate (−40 mV), and significantly increased spike generation in response to perithreshold ON input. These findings indicate that NE excites mitral cells directly via α1 receptors, an effect that may underlie, at least in part, increased mitral cell responses to weak ON input during locus coeruleus activation in vivo.

5-HT modulation of hyperpolarization-activated inward current and calcium-dependent outward current in a crustacean motor neuron

1992 ◽  
Vol 68 (2) ◽  
pp. 496-508 ◽  
Author(s):  
O. Kiehn ◽  
R. M. Harris-Warrick
Keyword(s):  
Motor Neuron ◽  
Time Course ◽  
Reversal Potential ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Inward Current ◽  
Calcium Dependent ◽  
Voltage Dependent ◽  
K Concentration ◽  
Conductance Increase

1. Serotonergic modulation of a hyperpolarization-activated inward current, Ih, and a calcium-dependent outward current, Io(Ca), was examined in the dorsal gastric (DG) motor neuron, with the use of intracellular recording techniques in an isolated preparation of the crab stomatogastric ganglion (STG). 2. Hyperpolarization of the membrane from rest with maintained current pulses resulted in a slow time-dependent relaxation back toward rest and a depolarizing overshoot after termination of the current pulse. In voltage clamp, hyperpolarizing commands negative to approximately -70 mV caused a slowly developing inward current, Ih, which showed no inactivation. Repolarization back to the holding potential of -50 mV revealed a slow inward tail current. 3. The reversal potential for Ih was approximately -35 mV. Raising extracellular K+ concentration ([K+]o) from 11 to 22 mM enhanced, whereas decreasing extracellular Na+ concentration ([Na+]o) reduced the amplitude of Ih. These results indicate that Ih in DG is carried by both K+ and Na+ ions. 4. Bath application of serotonin (5-HT; 10 microM) caused a marked increase in the amplitude of Ih through its active voltage ranges. 5. The time course of activation of Ih was well fitted by a single exponential function and strongly voltage dependent. 5-HT increased the rate of activation of Ih. 5-HT also slowed the rate of deactivation of the Ih tail on repolarization to -50 mV. 6. The activation curve for the conductance (Gh) underlying Ih was obtained by analyzing tail currents. 5-HT shifted the half activation for Gh from approximately -105 mV in control to -95 mV, resulting in an increase in the amplitude of Gh active at rest. 7. Two to 4 mM Cs+ abolished Ih, whereas barium (200 microM to 2 mM) had only weak suppressing effects on Ih. Concomitantly, Cs+ also blocked the 5-HT-induced inward current and conductance increase seen at voltages negative to rest. In current clamp, Cs+ caused DG to hyperpolarize 3-4 mV from rest, suggesting that Ih is partially active at rest and contributes to the resting membrane potential. 8. Depolarizing voltage commands from a holding potential of -50 mV resulted in a total outward current (Io) with an initial transient component and a sustained steady-state component. Application of 5-HT reduced both the transient and sustained components of Io. 9. Io was reduced by 10-20 mM tetraethylammonium (TEA), suggesting that it is primarily a K+ current.(ABSTRACT TRUNCATED AT 400 WORDS)

Currents under voltage clamp of burst-forming neurons of the cardiac ganglion of the lobster (Homarus americanus)

1986 ◽  
Vol 56 (6) ◽  
pp. 1739-1762 ◽  
Author(s):  
K. Tazaki ◽  
I. M. Cooke
Keyword(s):  
Voltage Clamp ◽  
Action Potentials ◽  
Reversal Potential ◽  
Outward Current ◽  
Homarus Americanus ◽  
Resting Potential ◽  
Molluscan Neurons ◽  
Cardiac Ganglion ◽  
Inward Current ◽  
Tail Current

Crustacean cardiac ganglion neuronal somata, although incapable of generating action potentials, produce regenerative, slow (greater than 200 ms) depolarizing potentials reaching -20 mV (from -50 mV) in response to depolarizing stimuli. These potentials initiate a burst of action potentials in the axon and are thus termed driver potentials. The somata of the anterior-most neurons (cells 1 or 2) were isolated by ligaturing for study of their membrane currents with a two-electrode voltage clamp. Inward current is attributed to Ca2+ by reason of dependence of driver potential amplitude on [Ca2+]0, independence of [Na+]0, resistance to tetrodotoxin, and inhibition by Cd (0.2 mM) and Mn (4 mM). Ca-mediated current (ICa) is present at -40 mV. It is optimally activated by a holding potential (Vh) of -50 to -60 mV and by clamps (command potential, Vc) to -10 mV. Time to peak (10-30 ms) and amplitude are strongly voltage dependent. Maximum tail-current amplitudes observed at -70 to -85 mV are ca. 100 nA. Inward tail peaks may not be resolved by our clamp (settling time, 2 ms). Tails relax with a time constant (tau) of approximately equal to 12 ms (at -70 to -85 mV). ICa exhibits inactivation in double pulse regimes. Recovery has a tau of approximately equal to 0.7 s. Tail current analyses indicate an exponential decline (tau approximately equal to 23 ms at -20 mV) toward a maintained amplitude of inward current tails. Analysis of outward currents indicates the presence of three conductance mechanisms having voltage dependences, time courses, and pharmacology similar to those of early outward current (IA), delayed outward current (IK), and outward current (IC) of molluscan neurons. Analysis of tail currents indicates a reversal potential for each of these near -75 mV, indicating that they are K currents. Early outward current, IA, shows a peak at 5 ms followed by rapid decline. Response to a second clamp given within 0.4 s is reduced; recovery is exponential, with a tau of approximately equal to 200 ms (at Vh = -50 mV). The amplitude of IA tested at 0 mV shows activation or deactivation by subthreshold shifts of Vh. The extent and rate of these changes shows voltage dependence (tau approximately equal to 100-500 ms for subthreshold prepulses). At the normal cell resting potential of -50 mV the amplitude of IA is 25% of that tested from -80 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

Bombesin-like peptides induce Ca2(+)-activated K+ conductance increases in mouse fibroblasts

1991 ◽  
Vol 260 (4) ◽  
pp. C701-C707 ◽  
Author(s):  
K. Kusano ◽  
H. Gainer
Keyword(s):  
Current Flow ◽  
Outward Current ◽  
Equilibrium Potential ◽  
Bathing Solution ◽  
Ionophore A23187 ◽  
3T3 Cells ◽  
Pipette Solution ◽  
Inward Current ◽  
Swiss 3T3 ◽  
Conductance Increase

Peptide receptor-activated membrane currents were studied in two mouse fibroblast cell lines, Swiss and Balb/c 3T3 cells, using a patch-electrode voltage-clamp technique. About 50% of the Swiss 3T3 cells examined responded to bombesin (Bn; 10(-9) to 10(-6) M), either by inducing outward current flow or inward current flow at the membrane holding potential (Vh) of -60 mV. The outward current type was more common (approximately 70%) than the inward current type (30%). The Bn-induced outward current (IBn) was reversed as the Vh was held to more negative than -90 mV (avg reversal potential, Erev = -82 mV). This Erev was closer to the equilibrium potential for K+ and shifted by altering the extracellular-to-intracellular K+ concentration ratio, in a Nernst-like relationship. The chance of recording this type of IBn was greatly reduced when K+ conductance blockers were present in the bathing solution (i.e., tetraethylammonium, Ba2+) or in the pipette solution (i.e., Cs). It was also reduced by recording with the pipette containing 5-10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. Application of Ca2+ ionophore A23187 (5 microM) induced a similar membrane current with conductance increase. Thus the outward IBn in Swiss 3T3 cells appears to be induced by the intracellular Ca2(+)-dependent K+ conductance increase. Applications of bradykinin (Bk), arginine vasopressin (AVP), neuromedin B (NmB), and gastrin releasing peptide (GRP) to Swiss 3T3 cells also induced receptor-activated currents similar to IBn. Balb/c 3T3 cells rarely generated outward currents in response to Bn, GRP, and NmB but did not respond to both AVP and Bk with outward current flows.

scholarly journals A pH-sensitive and voltage-dependent proton conductance in the plasma membrane of macrophages.

1993 ◽  
Vol 102 (4) ◽  
pp. 729-760 ◽  
Author(s):  
A Kapus ◽  
R Romanek ◽  
A Y Qu ◽  
O D Rotstein ◽  
S Grinstein
Keyword(s):  
Time Course ◽  
Reversal Potential ◽  
Outward Current ◽  
Peritoneal Macrophages ◽  
Equilibrium Potential ◽  
Acid Uptake ◽  
Similar Time ◽  
Cytosolic Ph ◽  
Whole Cell ◽  
Voltage Dependent

Phagocytes generate large amounts of metabolic acid during activation. Therefore, the presence of a conductive pathway capable of H+ extrusion has been suggested (Henderson, L. M., J. B. Chappell, and O. T. G. Jones. 1987. Biochemical Journal. 246:325-329). In this report, electrophysiological and fluorimetric methods were used to probe the existence of a H+ conductance in murine peritoneal macrophages. In suspended cells, recovery of the cytosolic pH (pHi) from an acid-load in Na+ and HCO3(-)-free medium was detectable in depolarizing but not in hyperpolarizing media. The rate of alkalinization was potentiated by the rheogenic ionophore valinomycin. These findings are consistent with the existence of a conductive H+ (equivalent) pathway. This notion was confirmed by patch-clamping and fluorescence ratio measurements of single adherent cells. When voltage was clamped in the whole-cell configuration, depolarizing pulses induced a sizable outward current which was accompanied by cytosolic alkalinization. Several lines of evidence indicate that H+ (equivalents) carry this current: (a) the conductance was unaffected by substitution of the major ionic constituents of the intra-and/or extracellular media, (b) the reversal potential of the tail currents approached the H+ equilibrium potential; and (c) the voltage-induced currents and pHi changes were both Zn2+ sensitive and had similar time course and potential dependence. The peak whole-cell current displayed marked outward rectification and was exquisitely H+ selective. At constant voltage, the H+ permeability was increased by lowering pHi but was inhibited by extracellular acidification. Together with the voltage dependence of the conductance, these features ensure that H+ extrusion can occur during activation, while potentially deleterious acid uptake is precluded. The properties of the conductance appear ideally suited for pHi regulation during phagocyte activation, because these cells undergo a sustained depolarization and an incipient acidification when stimulated. Comparison of the magnitude of the current with the amount of metabolic acid generated during macrophage activation indicates that the conductance is sufficiently large to contribute to the H+ extrusion required for maintenance of pHi.

Whole cell current analyses of pancreatic acinar AR42J cells. II. CCK and receptor-activated membrane currents

1991 ◽  
Vol 260 (5) ◽  
pp. C949-C957
Author(s):  
K. Kusano ◽  
H. Gainer
Keyword(s):  
Reversal Potential ◽  
Membrane Conductance ◽  
Pancreatic Acinar Cell ◽  
Bathing Solution ◽  
Ionophore A23187 ◽  
Whole Cell ◽  
Inward Current ◽  
Ar42j Cells ◽  
Voltage Dependent ◽  
Cl Conductance

Receptor currents generated in response to the application of sulfated octa-cholecystokinin (CCK) and various pancreatic secretagogues were studied in AR42J cells, a rat pancreatic acinar cell line. A whole cell configuration of the patch electrode voltage-clamp technique was utilized in these studies. Over 60% of the cells examined responded to 10(-6) M CCK by generating inward current at a membrane holding potential of -70 mV, accompanied by an increased membrane conductance. The CCK-induced receptor current (ICCK) was typically inactivated within 30 s in the presence of the ligand. The reversal potential (Erev) of the ICCK was approximately 0 mV when recorded in control bathing solution with a pipette containing 154 mM Cl-. When Cl- concentration in the bathing solution or in the recording pipette was modified, the Erev of the ICCK shifted toward the predicted Cl- potential. Na+ and K+ did not show significant contributions to the Erev of ICCK. Hence, the ICCK involves an increased Cl- conductance. This increased Cl- conductance appears to be due to an increase in intracellular Ca2+, since the ICCK could not be recorded from cells using pipettes containing 5 mM EGTA. Application of a Ca2+ ionophore A23187 (5 microM) to cells in control saline induced a similar inward current flow. The source of the Ca2+ involved in the ICCK appears to be mainly intracellular, since the ICCK could be recorded under conditions designed to completely block the voltage-dependent Ca2+ entry. These included exposure of the cells to a Ca2(+)-free saline for a brief period or the presence of 500 microM Cd2+ in the control bathing solution.

Heterogeneous Actions of Serotonin on Interneurons in Rat Visual Cortex

2003 ◽  
Vol 89 (3) ◽  
pp. 1278-1287 ◽  
Author(s):  
Zixiu Xiang ◽  
David A. Prince
Keyword(s):  
Receptor Antagonist ◽  
Receptor Agonist ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Pyramidal Cells ◽  
Equilibrium Potential ◽  
Inward Current ◽  
Outward Currents ◽  
Layer V

The effects of serotonin (5-HT) on excitability of two cortical interneuronal subtypes, fast-spiking (FS) and low threshold spike (LTS) cells, and on spontaneous inhibitory postsynaptic currents (sIPSCs) in layer V pyramidal cells were studied in rat visual cortical slices using whole-cell recording techniques. Twenty-two of 28 FS and 26 of 35 LTS interneurons responded to local application of 5-HT. In the group of responsive neurons, 5-HT elicited an inward current in 50% of FS cells and 15% of LTS cells, an outward current was evoked in 41% of FS cells and 81% of LTS cells, and an inward current followed by an outward current in 9% of FS cells and 4% LTS cells. The inward and outward currents were blocked by a 5-HT3 receptor antagonist, tropisetron, and a 5-HT1A receptor antagonist, NAN-190, respectively. The 5-HT–induced inward and outward currents were both associated with an increase in membrane conductance. The estimated reversal potential was more positive than −40 mV for the inward current and close to the calculated K+equilibrium potential for the outward current. The 5-HT application caused an increase, a decrease, or an increase followed by a decrease in the frequency of sIPSCs in pyramidal cells. The 5-HT3 receptor agonist 1-( m-chlorophenyl) biguanide increased the frequency of larger and fast-rising sIPSCs, whereas the 5-HT1Areceptor agonist (±)8-hydroxydipropylaminotetralin hydrobromide elicited opposite effects and decreased the frequency of large events. These data indicate that serotonergic activation imposes complex actions on cortical inhibitory networks, which may lead to changes in cortical information processing.

Ionic basis of the postsynaptic depolarizing GABA response in hippocampal pyramidal cells

1996 ◽  
Vol 76 (6) ◽  
pp. 3886-3894 ◽  
Author(s):  
K. L. Perkins ◽  
R. K. Wong
Keyword(s):  
Hippocampal Slices ◽  
Reversal Potential ◽  
Outward Current ◽  
Pyramidal Cells ◽  
Equilibrium Potential ◽  
Pipette Solution ◽  
Inward Current ◽  
Chloride Accumulation ◽  
Current Sequence ◽  
Ionic Basis

1. Whole cell voltage-clamp recording with recording pipette solutions of differing ionic composition was used to determine the ionic basis of the depolarizing gamma-aminobutyric acid (GABA) response. In the presence of 4-aminopyridine and excitatory amino acid receptor blockers, giant GABA-mediated postsynaptic currents (GPSCs) were recorded from CA3 pyramidal neurons in hippocampal slices from adult guinea pigs. With the GABAB component blocked, the GPSC was composed of an initial outward current (GABAA component) that peaked at 115 ms followed by a late inward current (GABAD component) that peaked at 400-600 ms. 2. Reduction of the intracellular concentration of potassium ([K+]i)resulted in no significant change in the reversal potential of the GABAD component of the GPSC, indicating that it is not a nonspecific cation current. 3. The HCO3- permeability of the channel mediating the GABAD response was assessed by using recording pipette solutions containing three different concentrations of bicarbonate ([HCO3-], 19, 49, and 102 mM). The reversal potential of the GABAD response shifted in the depolarizing direction as the HCO3- equilibrium potential was shifted in the depolarizing direction, indicating that the channel mediating the GABAD response is permeable to HCO3-. The reversal potential of the GABAD response was more sensitive to changes in recording pipette [HCO3-] than the reversal potential of the GABAA response, indicating that the GABAD response is carried by HCO3- to a greater extent than the GABAA response. 4. The outward current-inward current sequence of the biphasic GPSC was reversed to an inward current-outward current sequence by using a high [Cl-]/low [HCO3-] recording pipette solution (40 mM Cl-/6 mM HCO3-), indicating that the GABAA component is more sensitive to changes in [Cl-]i, and the GABAD component is more sensitive to changes in [HCO3-]i. 5. These data indicate that the GABAD component of the GPSC is predominantly carried by HCO3-. While this result supports the recently propsed chloride accumulation model, the model in its present form cannot explain the inward current-outward current polarity sequence of the GPSC recorded with the high [Cl-]/low [HCO3-] intracellular solution. The data obtained using that solution reveal the need for a more expansive chloride accumulation/ depletion model or for a model utilizing two distinct ionotropic GABA channels with different anion permeability ratios to account for the biphasic nature of the GPSC.

Nitric oxide mediates outward potassium currents in opossum esophageal circular smooth muscle

1996 ◽  
Vol 270 (6) ◽  
pp. G932-G938 ◽  
Author(s):  
J. Jury ◽  
K. R. Boev ◽  
E. E. Daniel
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Circular Muscle ◽  
Outward Current ◽  
Equilibrium Potential ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
Circular Smooth Muscle ◽  
Outward Currents

Single smooth muscle cells from the opossum body circular muscle were isolated and whole cell currents were characterized by the whole cell patch-clamp technique. When the cells were held at -50 mV and depolarized to 70 mV in 20-mV increments, initial small inactivating inward currents were evoked (-30 to 30 mV) followed by larger sustained outward currents. Depolarization from a holding potential of -90 mV evoked an initial fast inactivating outward current sensitive to 4-aminopyridine but not to high levels of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). The outward currents reversed near K+ equilibrium potential and were abolished when KCl was replaced by CsCl in the pipette solution. The sustained outward current was inhibited by quinine and cesium. High EGTA in the pipette solution reduced but did not abolish the sustained outward currents, suggesting that both Ca(2+)-dependent and -independent currents were evoked. The nitric oxide (NO)-releasing agents Sin-1 and sodium nitroprusside increased outward K+ currents. High levels of EGTA in the pipette solution abolished the increase in outward current induced by Sin-1. The presence of cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, blocked the effects of NO-releasing agents. We conclude that NO release activates K+ outward currents in opossum esophagus circular muscle, which may depend on Ca2+ release from the SR stores.

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.

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