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  • Title: Effect of internal and external K+ on Na+-Ca2+ exchange in dialyzed squid axons under voltage clamp conditions.
    Author: DiPolo R, Rojas H.
    Journal: Biochim Biophys Acta; 1984 Oct 03; 776(2):313-6. PubMed ID: 6477912.
    Abstract:
    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.
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