Effect of internal and external K+ on Na+-Ca2+ exchange in dialyzed squid axons under voltage clamp conditions.
The effect of external and internal K+ on Na+o-dependent Ca2+ efflux was studied in dialyzed squid axons under constant membrane potential. With axons clamped at their resting potentials, external K+ (up to 70 mM) has no effect on Na+-Ca2+ exchange. Removal of Ki+ causes a marked inhibition in the Na+o-dependent Ca2+ efflux component. Internal K+ activates the Na+-Ca2+ exchange with low affinity (K 1/2 = 90 mM). Activation by Ki+ is similar in the presence or in the absence of Na+i, thus ruling out a displacement of Na+i from its inhibitory site. Axons dialyzed with ATP also show a dependency of Ca2+ efflux on Ki+. The present results demonstrate that Ki+ is an important cofactor (partially required) for the proper functioning of the forward Na+-Ca2+ exchange.
D000818:Animals; D001369:Axons / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D049832:Decapodiformes; D003956:Dialysis; D008564:Membrane Potentials; D009441:Neurilemma / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D011188:Potassium; D002118:Calcium