Influence of the external concentration of potassium ions on functioning of voltage-dependent potassium channels in GH3 cells

1995 ◽  
Vol 27 (2) ◽  
pp. 85-89 ◽  
Author(s):  
A. V. Grishchenko ◽  
N. M. Berezetskaya ◽  
G. E. Weinreb ◽  
N. I. Kononenko ◽  
M. B. Sedova
Keyword(s):  
Potassium Channels ◽  
Gh3 Cells ◽  
Potassium Ions ◽  
External Concentration ◽  
Voltage Dependent

scholarly journals Pandinus imperator scorpion venom blocks voltage-gated potassium channels in GH3 cells.

1988 ◽  
Vol 91 (6) ◽  
pp. 817-833 ◽  
Author(s):  
P A Pappone ◽  
M T Lucero
Keyword(s):  
Potassium Channels ◽  
Potassium Channel ◽  
Potassium Current ◽  
Potassium Currents ◽  
Scorpion Venom ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Crude Venom ◽  
Voltage Gated ◽  
Voltage Dependent

We examined the effects of Pandinus imperator scorpion venom on voltage-gated potassium channels in cultured clonal rat anterior pituitary cells (GH3 cells) using the gigohm-seal voltage-clamp method in the whole-cell configuration. We found that Pandinus venom blocks the voltage-gated potassium channels of GH3 cells in a voltage-dependent and dose-dependent manner. Crude venom in concentrations of 50-500 micrograms/ml produced 50-70% block of potassium currents measured at -20 mV, compared with 25-60% block measured at +50 mV. The venom both decreased the peak potassium current and shifted the voltage dependence of potassium current activation to more positive potentials. Pandinus venom affected potassium channel kinetics by slowing channel opening, speeding deactivation slightly, and increasing inactivation rates. Potassium currents in cells exposed to Pandinus venom did not recover control amplitudes or kinetics even after 20-40 min of washing with venom-free solution. The concentration dependence of crude venom block indicates that the toxins it contains are effective in the nanomolar range of concentrations. The effects of Pandinus venom were mimicked by zinc at concentrations less than or equal to 0.2 mM. Block of potassium current by zinc was voltage dependent and resembled Pandinus venom block, except that block by zinc was rapidly reversible. Since zinc is found in crude Pandinus venom, it could be important in the interaction of the venom with the potassium channel. We conclude that Pandinus venom contains toxins that bind tightly to voltage-dependent potassium channels in GH3 cells. Because of its high affinity for voltage-gated potassium channels and its irreversibility, Pandinus venom may be useful in the isolation, mapping, and characterization of voltage-gated potassium channels.

scholarly journals Blockage of the light-sensitive conductance in hyperpolarizing photoreceptors of the scallop. Effects of tetraethylammonium and 4-aminopyridine.

1994 ◽  
Vol 104 (3) ◽  
pp. 487-505 ◽  
Author(s):  
M D Gomez ◽  
E Nasi
Keyword(s):  
Potassium Channels ◽  
Light Sensitivity ◽  
Rapid Onset ◽  
Potassium Ions ◽  
The Family ◽  
Cell Recording ◽  
Voltage Dependent ◽  
A Site ◽  
Membrane Treatment ◽  
Phototransduction Cascade

The tight-seal whole-cell recording technique was used to examine the effect of tetraethylammonium (TEA) and 4-aminopyridine (4-AP) on the photocurrent of hyperpolarizing ciliary photoreceptors isolated from the distal retina of the bay scallop (Pecten irradians). In these cells, light causes an increase in a conductance that is highly selective to potassium ions. Extracellular application of TEA at a concentration of 50 mM produced a modest, reversible block (approximately 35% at -20 mV holding potential). The blockage was weakly voltage dependent, increasing by approximately 20% for a 20-mV hyperpolarization, suggestive of a site of interaction superficially located within the electric field of the membrane. Treatment with TEA produced no significant changes either in the light sensitivity of the photocurrent or in its kinetics. The effects of superfusion with 4-AP were more dramatic: the light-evoked current was nearly abolished (> 95%) at submillimolar concentrations, with a half-maximal dose of approximately 0.6 microns. The blockage had a rapid onset and was slowly reversible. No significant use or voltage dependency were observed. A number of control experiments indicated that the phototransduction cascade remained functional during treatment with 4-AP: the early receptor current, the prolonged after current and its suppression, the photoresponse kinetics and the light sensitivity of the cell were little affected by 4-AP, suggesting that the suppression of the photocurrent is due to blockage of the light-sensitive channels, rather than impairment of some of the activation steps. The results are discussed in the light of a possible kinship between the light-activated potassium channels of invertebrate hyperpolarizing photoreceptors and the family of rapidly-inactivating voltage-dependent potassium channels, which typically exhibit high susceptibility to blockage by this drug.

scholarly journals Interaction between tetraethylammonium and amino acid residues in the pore of cloned voltage-dependent potassium channels.

1991 ◽  
Vol 266 (12) ◽  
pp. 7583-7587
Author(s):  
M P Kavanaugh ◽  
M D Varnum ◽  
P B Osborne ◽  
M J Christie ◽  
A E Busch ◽  
...  
Keyword(s):  
Amino Acid ◽  
Potassium Channels ◽  
Amino Acid Residues ◽  
Voltage Dependent

scholarly journals Activation-inactivation of potassium channels and development of the potassium-channel spike in internally perfused squid giant axons.

1981 ◽  
Vol 78 (1) ◽  
pp. 43-61 ◽  
Author(s):  
I Inoue
Keyword(s):  
Potassium Channels ◽  
Potassium Channel ◽  
Voltage Clamp ◽  
Time Constant ◽  
Equilibrium Potential ◽  
Giant Axons ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Time Courses ◽  
Calcium Permeability

A spike that is the result of calcium permeability through potassium channels was separated from the action potential is squid giant axons internally perfused with a 30 mM NaF solution and bathed in a 100 mM CaCl2 solution by blocking sodium channels with tetrodotoxin. Currents through potassium channels were studied under voltage clamp. The records showed a clear voltage-dependent inactivation of the currents. The inactivation was composed of at least two components; one relatively fast, having a time constant of 20--30 ms, and the other very slow, having a time constant of 5--10 s. Voltage clamp was carried out with a variety of salt compositions in both the internal and external solutions. A similar voltage-dependent inactivation, also composed of the two components, was recognized in all the current through potassium channels. Although the direction and intensity of current strongly depended on the salt composition of the solutions, the time-courses of these currents at corresponding voltages were very similar. These results strongly suggest that the inactivation of the currents in attributable to an essential, dynamic property of potassium channels themselves. Thus, the generation of a potassium-channel spike can be understood as an event that occurs when the equilibrium potential across the potassium channel becomes positive.

A background sodium conductance is necessary for spontaneous depolarizations in rat pituitary cell line GH3

1994 ◽  
Vol 266 (3) ◽  
pp. C709-C719 ◽  
Author(s):  
S. M. Simasko
Keyword(s):  
Cell Line ◽  
Calcium Current ◽  
Membrane Conductance ◽  
Potassium Currents ◽  
Pituitary Cell ◽  
Calcium Currents ◽  
Gh3 Cells ◽  
Sodium Conductance ◽  
Rat Pituitary ◽  
Voltage Dependent

The role of Na+ in the expression of membrane potential activity in the clonal rat pituitary cell line GH3 was investigated using the perforated patch variation of patch-clamp electrophysiological techniques. It was found that replacing bath Na+ with choline, tris(hydroxymethyl)aminomethane (Tris), or N-methyl-D-glucamine (NMG) caused the cells to hyperpolarize 20-30 mV. Tetrodotoxin had no effect. The effects of the Na+ substitutes could not be explained by effects on potassium or calcium currents. Although all three Na+ substitutes suppressed voltage-dependent calcium current by 10-20%, block of voltage-dependent calcium current by nifedipine or Co2+ did not result in hyperpolarization of the cells. There was no effect of the Na+ substitutes on voltage-dependent potassium currents. In contrast, all three Na+ substitutes influenced calcium-activated potassium currents [IK(Ca)], but only at depolarized potentials. Choline consistently suppressed IK(Ca), whereas Tris and NMG either had no effect or slightly increased IK(Ca). These effects on IK(Ca) also cannot explain the hyperpolarization induced by removing bath Na+. Choline always hyperpolarized cells yet suppressed IK(Ca). Furthermore, removing bath Na+ caused an increase in cell input resistance, an observation consistent with the loss of a membrane conductance as the basis of the hyperpolarization. Direct measurement of background currents revealed a 12-pA inward current at -84 mV that was lost upon removing bath Na+. These results suggest that this background sodium conductance provides the depolarizing drive for GH3 cells to reach the threshold for firing calcium-dependent action potentials.

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