The effect of the internal sodium concentration on calcium fluxes in isolated guinea‐pig auricles

1. Calcium efflux from guinea‐pig auricles followed saturation kinetics when [Ca]o and [Na]o were changed while the ratio [Ca]o/[Na]o2 was kept constant. The Michaelis constant, KmCa+Na = 40 m M, suggests that a hypothetical carrier system, responsible for sodium—calcium exchange, is far from saturation with the inside concentrations of these ions.