scholarly journals Potassium current and the effect of cesium on this current during anomalous rectification of the egg cell membrane of a starfish.

1976 ◽  
Vol 67 (6) ◽  
pp. 621-638 ◽  
Author(s):  
S Hagiwara ◽  
S Miyazaki ◽  
N P Rosenthal
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Time Dependent ◽  
Equilibrium Potential ◽  
K Channel ◽  
Egg Cell ◽  
Dimensionless Number ◽  
First Order Kinetics ◽  
K Current ◽  
Kinetics Of

The kinetics of the membrane current during the anomalous or inward-going rectification of the K current in the egg cell membrane of the starfish Mediaster aequalis were analyzed by voltage clamp. The rectification has instantaneous and time-dependent components. The time-dependent increase in the K conductance for the negative voltage pulse as well as the decrease in the conductance for the positive pulse follows first-order kinetics. The steady-state conductance increases as the membrane potential becomes more negative and reaches the saturation value at about -40 mV more negative than the K equilibrium potential, V(K). The entire K conductance can be expressed by g(K).n; g g(K) represents the component for the time-independent conductance which depends on V-V(K) and [K+]o, and n is a dimensionless number (1 is greater than or equal to n is greater than or equal to 0) and determined by two rate constants which depend only on V-V(K). Cs+ does not carry any significant current through the K channel but blocks the channel at low concentration in the external medium. The blocking effect increases as the membrane potential is made more negative and the potential-dependent blocking by the external Cs+ also has instantaneous and time-dependent components.

Potentiation of Ca(2+)-activated secretory activity by a cAMP-mediated mechanism in avian salt gland cells

1994 ◽  
Vol 267 (1) ◽  
pp. C255-C265 ◽  
Author(s):  
S. C. Martin ◽  
J. Thompson ◽  
T. J. Shuttleworth
Keyword(s):  
Membrane Potential ◽  
Driving Force ◽  
Secretory Activity ◽  
Salt Gland ◽  
Receptor Activation ◽  
Equilibrium Potential ◽  
K Channel ◽  
Patch Clamp Technique ◽  
Cl Secretion ◽  
K Current

In the avian salt gland carbachol (CCh) evokes oscillations in K+ and Cl- current that are sufficient to fully activate secretory activity. Employing the perforated patch-clamp technique, we demonstrate that beta-adrenergic receptor activation stimulates a sustained adenosine 3',5'-cyclic monophosphate (cAMP)-dependent Cl- current with no increase in K+ current. This evokes only a modest increase in secretory activity. However, application of isoproterenol in the presence of a threshold dose of CCh results in maximal secretory activity. Membrane potential measurements demonstrate that isoproterenol stimulates a sustained membrane depolarization from approximately -45 mV to the Cl- equilibrium potential (ECl), whereas CCh evokes oscillations in membrane potential to levels more negative than ECl, representing a mixture of K+ and Cl- conductances. We conclude that, in agreement with current models of fluid secretion, maximal stimulation can only be achieved with simultaneous activation of both K+ and Cl- currents. Because isoproterenol fails to stimulate a K+ current, Cl- secretion is reduced as the driving force for Cl- secretion is dissipated. However, if a driving force is imposed by increasing K+ channel activity (by coadministering CCh), Cl- efflux is sustained. These results could provide a basis for the marked potentiation of Ca(2+)-mediated secretion by agonists that increase cAMP seen in in vivo studies of salivary glands and other exocrine tissues.

scholarly journals Activation of Ca(2+)-dependent K+ current by acetylcholine and histamine in a human gastric epithelial cell line.

1993 ◽  
Vol 102 (4) ◽  
pp. 667-692 ◽  
Author(s):  
E Hamada ◽  
T Nakajima ◽  
S Ota ◽  
A Terano ◽  
M Omata ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Epithelial Cell ◽  
Cell Line ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Induced Response ◽  
Epithelial Cell Line ◽  
Bathing Solution ◽  
Pipette Solution ◽  
K Current

The effects of acetylcholine (ACh) and histamine (His) on the membrane potential and current were examined in JR-1 cells, a mucin-producing epithelial cell line derived from human gastric signet ring cell carcinoma. The tight-seal, whole cell clamp technique was used. The resting membrane potential, the input resistance, and the capacitance of the cells were approximately -12 mV, 1.4 G ohms, and 50 pF, respectively. Under the voltage-clamp condition, no voltage-dependent currents were evoked. ACh or His added to the bathing solution hyperpolarized the membrane by activating a time- and voltage-independent K+ current. The ACh-induced hyperpolarization and K+ current persisted, while the His response desensitized quickly (< 1 min). These effects of ACh and His were mediated predominantly by m3-muscarinic and H1-His receptors, respectively. The K+ current induced by ACh and His was inhibited by charybdotoxin, suggesting that it is a Ca(2+)-activated K+ channel current (IK.Ca). The measurement of intracellular Ca2+ ([Ca2+]i) using Indo-1 revealed that both agents increased [Ca2+]i with similar time courses as they increased IK.Ca. When EGTA in the pipette solution was increased from 0.15 to 10 mM, the induction of IK.Ca by ACh and His was abolished. Thus, both ACh and His activate IK.Ca by increasing [Ca2+]i in JR-1 cells. In the Ca(2+)-free bathing solution (0.15 mM EGTA in the pipette), ACh evoked IK.Ca transiently. Addition of Ca2+ (1.8 mM) to the bath immediately restored the sustained IK.Ca. These results suggest that the ACh response is due to at least two different mechanisms; i.e., the Ca2+ release-related initial transient activation and the Ca2+ influx-related sustained activation of IK.Ca. Probably because of desensitization, the Ca2+ influx-related component of the His response could not be identified. Intracellularly applied inositol 1,4,5-trisphosphate (IP3), with and without inositol 1,3,4,5-tetrakisphosphate (IP4), mimicked the ACh response. IP4 alone did not affect the membrane current. Under the steady effect of IP3 or IP3 plus IP4, neither ACh nor His further evoked IK.Ca. Intracellular application of heparin or of the monoclonal antibody against the IP3 receptor, mAb18A10, inhibited the ACh and His responses in a concentration-dependent fashion. Neomycin, a phospholipase C (PLC) inhibitor, also inhibited the agonist-induced response in a concentration-dependent fashion. Although neither pertussis toxin (PTX) nor N-ethylmaleimide affected the ACh or His activation of IK,Ca, GDP beta S attenuated and GTP gamma S enhanced the agonist response.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of intracellular potassium and sodium injections on the inhibitory postsynaptic potential

1964 ◽  
Vol 160 (979) ◽  
pp. 181-196 ◽  
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Cell Membrane ◽  
Direct Evidence ◽  
Equilibrium Potential ◽  
Ionic Mechanism ◽  
Half Time ◽  
Intracellular Potassium ◽  
Postsynaptic Potential ◽  
Almost All

Two barrels of double microelectrodes have been filled with different salts so that the electrophoretic injection of Na + and K + ions could be investigated in alternating sequence on the same motoneuron in the cat spinal cord. The effects of these injections on the mechanism generating the IPSP were evaluated by determining the equilibrium potential for the IPSP (the E IPSP ), i. e. the membrane potential at which the IPSP is zero. Such determinations have been made every 5 to 10 s after ion injections and have provided the most direct evidence of the ionic mechanism generating the IPSP . Comparison of the Na + and K + ion injections shows that the former injection always displaced the E IPSP much farther in the depolarizing direction and that recovery was much slower, with a half-time of 70 to 120 s, in contrast to about 20 s after the K + injection. In the discussion and evaluation of these results it was postulated that almost all of the displacement of the E IPSP in the depolarizing direction was due to the increased intracellular Cl - concentration, the (Cl - ) i . Under normal conditions a high (Cl - ) i declines by diffusional exchange across the cell membrane with a half-time of about 20 s, but this decline is much slower when the internal potassium is depleted. An explanation of this difference will be given in the following paper.

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.

Diverse current and voltage responses to baclofen in an identified molluscan photoreceptor

1995 ◽  
Vol 74 (2) ◽  
pp. 506-518 ◽  
Author(s):  
L. D. Matzel ◽  
I. A. Muzzio ◽  
R. F. Rogers
Keyword(s):  
Voltage Clamp ◽  
Action Potentials ◽  
Gabab Receptor ◽  
Outward Current ◽  
Gabab Receptors ◽  
Equilibrium Potential ◽  
K Channel ◽  
Electrode Voltage ◽  
Voltage Dependent ◽  
K Current

1. gamma-Aminobuturic acid-B (GABAB) receptors play a role in the mediation of slow inhibitory postsynaptic potentials in mammalian as well as some nonmammalian species. In identified photoreceptors from the marine mollusc Hermissenda, recent evidence has suggested that GABA, as well as the GABAB receptor agonist baclofen, might simultaneously modulate multiple conductances on the postsynaptic membrane. Here, using intracellular current-clamp and single-electrode voltage-clamp techniques, we have characterized responses to baclofen in the B photoreceptors of the Hermissenda eye. 2. Microapplication of baclofen (12.5–62.5 microM) to the terminal branches of the B photoreceptors induced a slow, concentration-dependent hyperpolarization (approximately 3–8 mV) that was accompanied by a cessation of spontaneous action potentials and a positive shift in firing threshold. Both the hyperpolarization and the shift in spike threshold in response to baclofen were attenuated largely by the K+ channel blocker tetraethylammonium chloride (TEA; 50 mM). 3. Bath application of baclofen (100 microM) decreased the amplitude, duration, and the afterhyperpolarization (AHP) of evoked action potentials. Although baclofen's effect on spike duration and amplitude persisted in the absence of extracellular Ca2+, the reduction of the AHP by baclofen was eliminated, suggesting that multiple conductances mediated the baclofen-induced modification of the action potential. 4. Using a single-electrode voltage-clamp technique, microapplication of baclofen to the terminal branches of the B photoreceptor produced a slow, net outward current (< 0.5 nA) that reversed near the equilibrium potential for K+ and shifted to more positive potentials when extracellular K+ was increased, in approximate agreement with the Nernst equation for K+. 5. Baclofen induced an increase in amplitude of the nonvoltage dependent leak conductance (IL), and the increase was blocked by TEA. The baclofen-induced increase of IL was accompanied by an increase in amplitude and a negative shift in the voltage dependence of a slow, steeply voltage-dependent K+ current (IK), which displays selective sensitivity to TEA but does not normally contribute to leak conductance. The amplitude and steady-state inactivation of a fast, transient K+ current, as well as the amplitude of an inwardly rectifying K+ current were unaffected by baclofen. 6. Both the rate of activation as well as the amplitude of a voltage-dependent Ca2+ current (ICa) were reduced by baclofen. The reduction of ICa resulted in a concomitant suppression of a Ca(2+)-dependent K+ current (IK-Ca) that was sufficient to account for the reduction of the AHP after evoked action potentials.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals K+ channels of stomatal guard cells. Characteristics of the inward rectifier and its control by pH.

1992 ◽  
Vol 99 (4) ◽  
pp. 615-644 ◽  
Author(s):  
M R Blatt
Keyword(s):  
Intracellular Ph ◽  
Guard Cells ◽  
Inward Rectifier ◽  
Equilibrium Potential ◽  
Egg Cell ◽  
K Channels ◽  
Inward Rectifiers ◽  
Stomatal Guard Cells ◽  
K Current ◽  
Current Reversal

Intracellular microelectrode recordings and a two-electrode voltage clamp have been used to characterize the current carried by inward rectifying K+ channels of stomatal guard cells from the broadbean, Vicia faba L. Superficially, the current displayed many features common to inward rectifiers of neuromuscular and egg cell membranes. In millimolar external K+ concentrations (Ko+), it activated on hyperpolarization with half-times of 100-200 ms, showed no evidence of time- or voltage-dependent inactivation, and deactivated rapidly (tau approximately 10 ms) on clamping to 0 mV. Steady-state conductance-voltage characteristics indicated an apparent gating charge of 1.3-1.6. Current reversal showed a Nernstian dependence on Ko+ over the range 3-30 mM, and the inward rectifier was found to be highly selective for K+ over other monovalent cations (K+ greater than Rb+ greater than Cs+ much greater than Na+). Unlike the inward rectifiers of animal membranes, the current was blocked by charybdotoxin and alpha-dendrotoxin (Kd much less than 50 nM), as well as by tetraethylammonium chloride (K1/2 = 9.1 mM); gating of the guard cell K+ current was fixed to voltages near -120 mV, independent of Ko+, and the current activated only with supramillimolar K+ outside (EK+ greater than -120 mV). Most striking, however, was inward rectifier sensitivity to [H+] with the K+ current activated reversibly by mild acid external pH. Current through the K+ inward rectifier was found to be largely independent of intracellular pH and the current reversal (equilibrium) potential was unaffected by pHo from 7.4 to 5.5. By contrast, current through the K+ outward rectifier previously characterized in these cells (1988. J. Membr. Biol. 102:235) was largely insensitive to pHo, but was blocked reversibly by acid-going intracellular pH. The action of pHo on the K+ inward rectifier could not be mimicked by extracellular Ca2+ for which changes in activation, deactivation, and conductance were consonant with an effect on surface charge ([Ca2+] less than or equal to 1 mM). Rather, extracellular pH affected activation and deactivation kinetics disproportionately, with acid-going pHo raising the K+ conductance and shifting the conductance-voltage profile positive-going along the voltage axis and into the physiological voltage range. Voltage and pH dependencies for gating were consistent with a single, titratable group (pKa approximately 7 at -200 mV) residing deep within the membrane electric field and accessible from the outside.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals The Influence of the Intracellular Potential on Potassium Uptake by Beetroot Tissue

1966 ◽  
Vol 49 (3) ◽  
pp. 551-563 ◽  
Author(s):  
Ronald J. Poole
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Cell Membrane ◽  
Metabolic Activity ◽  
Transport Process ◽  
Equilibrium Potential ◽  
Bicarbonate Concentration ◽  
K Uptake ◽  
Active Transport Process ◽  
Metabolic Transport

Intracellular potentials were measured in beetroot tissue during the steady-state uptake of K+ from various solutions. In solutions containing bicarbonate, the membrane potential becomes up to 70 mv more negative than the estimated equilibrium potential for K+. The uptake of K+ from such solutions is correlated with variations in the potential, both when the bicarbonate concentration is changed and also when the metabolic activity of the tissue is changed by washing in water for various periods. However, the estimated permeability to K+ varies from 0.4 x 10-7 to 1.5 x 10-7 cm·sec-1. It is postulated that the change of potential arises from the metabolic transport of HCO3- into the cell or H+ outwards, and that the associated uptake of K+ is partly or entirely by passive diffusion across the cell membrane. In contrast, K+ uptake from KCl solutions is not accompanied by any significant change in the membrane potential, which remains relatively close to the K+ equilibrium potential. In solutions containing both KHCO3 and KCl, it appears that an amount of K+ equal to the influx of Cl- is taken up independently of the potential, while the component of K+ uptake which is not balanced by Cl- uptake is related to the potential in the manner described. These results suggest that K+ uptake is linked to Cl- uptake in an electrically neutral active transport process.

scholarly journals Dynamics of aminopyridine block of potassium channels in squid axon membrane.

1976 ◽  
Vol 68 (5) ◽  
pp. 519-535 ◽  
Author(s):  
J Z Yeh ◽  
G S Oxford ◽  
C H Wu ◽  
T Narahashi
Keyword(s):  
Time Course ◽  
Membrane Surface ◽  
K Channel ◽  
Dependent Manner ◽  
Squid Axon ◽  
Axon Membrane ◽  
K Channels ◽  
Voltage Dependent ◽  
K Current ◽  
Kinetics Of

Aminopyridines (2-AP, 3-AP, and 4-AP) selectively block K channels of squid axon membranes in a manner dependent upon the membrane potential and the duration and frequency of voltage clamp pulses. They are effective when applied to either the internal or the external membrane surface. The steady-state block of K channels by aminopyridines is more complete for low depolarizations, and is gradually relieved at higher depolarizations. The K current in the presence of aminopyridines rises more slowly than in control, the change being more conspicuous in 3-AP and 4-AP than in 2-AP. Repetitive pulsing relieves the block in a manner dependent upon the duration and interval of pulses. The recovery from block during a given test pulse is enhanced by increasing the duration of a conditioning depolarizing prepulse. The time constant for this recovery is in the range of 10-20 ms in 3-AP and 4-AP, and shorter in 2-AP. Twin pulse experiments with variable pulse intervals have revealed that the time course for re-establishment of block is much slower in 3-AP and 4-AP than in 2-AP. These results suggest that 2-AP interacts with the K channel more rapidly than 3-AP and 4-AP. The more rapid interaction of 2-AP with K channels is reflected in the kinetics of K current which is faster than that observed in 3-AP or 4-AP, and in the pattern of frequency-dependent block which is different from that in 3-AP or 4-AP. The experimental observations are not satisfactorily described by alterations of Hodgkin-Huxley n-type gating units. Rather, the data are consistent with a simple binding scheme incorporating no changes in gating kinetics which conceives of aminopyridine molecules binding to closed K channels and being released from open channels in a voltage-dependent manner.

Inward rectifier K+ channel Kir2.3 is localized at the postsynaptic membrane of excitatory synapses

2002 ◽  
Vol 282 (6) ◽  
pp. C1396-C1403 ◽  
Author(s):  
Atsushi Inanobe ◽  
Akikazu Fujita ◽  
Minoru Ito ◽  
Hitonobu Tomoike ◽  
Kiyoshi Inageda ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Granule Cells ◽  
Pdz Domain ◽  
Postsynaptic Membrane ◽  
Equilibrium Potential ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Kir Channel ◽  
Anchoring Proteins

Classical inwardly rectifying K+ channels (Kir2.0) are responsible for maintaining the resting membrane potential near the K+ equilibrium potential in various cells, including neurons. Although Kir2.3 is known to be expressed abundantly in the forebrain, its precise localization has not been identified. Using an antibody specific to Kir2.3, we examined the subcellular localization of Kir2.3 in mouse brain. Kir2.3 immunoreactivity was detected in a granular pattern in restricted areas of the brain, including the olfactory bulb (OB). Immunoelectron microscopy of the OB revealed that Kir2.3 immunoreactivity was specifically clustered on the postsynaptic membrane of asymmetric synapses between granule cells and mitral/tufted cells. The immunoprecipitants for Kir2.3 obtained from brain contained PSD-95 and chapsyn-110, PDZ domain-containing anchoring proteins. In vitro binding assay further revealed that the COOH-terminal end of Kir2.3 is responsible for the association with these anchoring proteins. Therefore, the Kir channel may be involved in formation of the resting membrane potential of the spines and, thus, would affect the response of N-methyl-d-aspartic acid receptor channels at the excitatory postsynaptic membrane.

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