Voltage-sensitive potassium channels in Limulus ventral photoreceptors.
The steady-state slope conductance of Limulus ventral photoreceptors increases markedly when the membrane is depolarized from rest. The ionic basis of this rectification has been examined with a voltage-clamp technique. Tail currents that occur when membrane potential is repolarized after having been depolarized have been identified. The tail currents reverse direction at a voltage that becomes more positive when Ko is increased. Rectification is reduced by extracellular 4-aminopyridine and by intracellular injection of tetra-ethyl-ammonium (TEA). These results indicate that the membrane rectification around resting potential is due primarily to voltage-sensitive K+ channels. The increase in gK caused by depolarization is not mediated by a voltage-dependent rise in in Cai++, since intracellular injection of Ca++ causes a decrease rather than an increase in slope conductance. TEA can be used to examine the functional role of the K+ channels because it blocks them without substantially affecting the light-activated Na+ conductance. The effect of TEA on response-intensity curves shows that the K+ channels serve to compress the voltage range of receptor potentials.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects; D006737:Horseshoe Crabs / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects*; D008954:Models, Biological; D009994:Osmolar Concentration; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D011725:Pyridines / Q000494:pharmacology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D011725:Pyridines; D013757:Tetraethylammonium Compounds; D011188:Potassium; D002118:Calcium