[Efflux of 36Cl and the distribution of chlorine in the papillary muscles of rabbits and the effect of ouabain].

The 36Cl efflux "in vivo" was measured in the rabbit papillary muscle to determine the Cl distribution in the muscle and to evaluate the effect of ouabain on this parameter. The results obtained for the 36Cl efflux are analyzed using either a two-compartment model or a model including diffusion in the extracellular space in series with one compartment. The Cl exchange with 36Cl, [Cl]i (intracellular Cl content which has participated in exchange, Cl in equilibrium with 36Cl) is computed from the exponential terms of the models. A time exposure of 40 and 80 min to the 36Cl-containing solution led to the same exchange Cl content: 20.5 and 23.9 mmol/kg cells. Addition of ouabain (10(-6) M) slightly increased the rate constant of the cellular compartment, but did not influence the [Cl]i. In the presence of ouabain (10(-6) M), there was a significant increase in the efflux component with a rapid rate constant. These results can be interpreted as follows: the Cl intracellular concentration is not affected by ouabain; thus, the increase in total Cl content induced in the papillary muscle by ouabain is located in a compartment having a very rapid exchange velocity with the extracellular medium.