Transmembrane chloride flux in tissue-cultured chick heart cells.

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Abstract
To evaluate the transmembrane movement of chloride in a preparation of cardiac muscle lacking the extracellular diffusion limitations of natural specimens, intracellular chloride concentration ([Cl]i) and transmembrane 36Cl efflux were determined in growth-oriented embryonic chick heart cells in tissue culture. Using the method of isotopic equilibrium, [Cl]i was 25.1 .+-. 7.3 mmol .cntdot. (liter cell water)-1, comparable to the value of 24.9 .+-. 5.4 mmol .cntdot. (liter cell water)-1 determined by coulometric titration. Two cellular 36Cl compartments were found; 1 exchanged with a rate constant of 0.67 .+-. 0.12 min-1 and was associated with the cardiac muscle cells; the other, attributed to the fibroblasts, exchanged with a rate constant of 0.18 .+-. 0.05 min-1. At 37.degree. C, transmembrane Cl flux of cardiac muscle under steady-state conditions was 30 pmol .cntdot. cm-2 .cntdot. s-1. In K-free, normal, or high-Ko solutions, the responses of the membrane potential to changes in external Cl concentration suggested that chloride conductance was low. Cl transport across the myocardial cell membrane apparently is more rapid than K transport and is largely electrically silent.