Whole-cell recordings of chloride currents in cultured human skeletal muscle.

Chloride currents in human myoballs were investigated with the tight-seal whole-cell recording method in a wide range of membrane voltages (-125 to +145 mV). Two current components having different kinetics could be distinguished. In more than 90% of the myoballs the following results were obtained. At negative potentials, the amplitude of the Cl- current was small and independent of time. The amplitude of the current increased as the membrane potential was made more positive. At potentials positive to +75 mV, the current increased monoexponentially with time. Inactivation occurred only during very long (greater than 3 s) pulses. When such a test pulse was preceded by a conditioning pulse to +60 mV, the current at potentials more than +90 mV was markedly smaller than in the absence of a prepulse, and no activation was provoked by strongly pulses. Recovery from inactivation could only be measured at potentials negative to -40 mV. The Cl- conductance at -85 mV was 5.9 +/- 3.64 microS/cm2 (SD; n = 10). In about 5% of the myoballs a kinetically different current was visible, characterized by fast inactivation at highly positive potentials. The current amplitudes were substantially larger in such cases, the Cl- conductance at -85 mV being 12.2 +/- 9.02 microS/cm2 (n = 4).