Voltage- and time-dependent chloride currents in chick skeletal muscle cells grown in tissue culture

Membrane chloride currents in chick skeletal muscle cells grown in tissue culture were studied by use of the whole cell variation of the patch electrode voltage clamp technique. Small diameter myoballs were obtained by adding colchicine to the growth media. To isolate the currents through the chloride channels, the currents through the sodium, calcium and potassium channels were minimized. With symmetrical chloride concentrations bathing the membrane, inward currents were activated by depolarizations above -45 mV. Above 0 mV, the currents became outward. The reversal potential for the currents shifted with the chloride concentration gradient in a manner consistent with the Nernst relation, indicating that the currents were predominantly carried by chloride ions. The instantaneous current-voltage relation obtained from tail current data was linear. The relationship between conductance and membrane potential was sigmoid. The conductance activated above -45 mV, increased steeply between -45 and -10 mV and saturated above +20 mV. Over the range of potentials where the conductance was just beginning to activate, the conductance increased e-fold for a 7 mV depolarization. The currents activated with an exponential time course and did not decline during step depolarizations. Tail currents declined slowly as the sum of two exponential components. The currents were reversibly suppressed by 100 microM SITS and were irreversibly suppressed by 10 microM DIDS.