The Kinetic Analysis of Simultaneous Calcium Exchange and Sorbitol Washout in the Rat Heart

Abstract

Summary

In isolated working rat hearts, the washout of ³H sorbitol as well as the exchange of ⁴⁵Ca²⁺ could be described as the sum of three processes, two of which were found to be exponential in nature. The volume of distribution of ⁴⁵Ca²⁺ was greater than that of the sorbitol. This greater volume of distribution was clearest for the compartment with the longest time constant. Addition of quinidine in doses which produced a 32% decline in maximum dP/dt had no effect on the rate constants for the washout of sorbitol or the exchange of ⁴⁵Ca²⁺. The difference between the volume of distribution of calcium and sorbitol was also not measurably changed by the negative inotropic intervention.

The results suggest that the kinetics of ⁴⁵Ca²⁺ exchange are determined by those processes which limit the washout of the extracellular space. The studies with quinidine further suggest that if this agent displaces Ca²⁺ from binding or storage sites, the amount affected is too small to be detected by kinetic analysis of calcium exchange in the rat heart.