Kinetic properties of the chloride conductance of frog muscle.

1. The anion conductance of frog muscle has been studied at alkaline, neutral and acid extracellular pH values using a voltage clamp technique. Potassium in the extracellular solution was replaced by rubidium in order to simplify the behavior of the cation conductance.2. At pH 9.8 the chloride conductance fell exponentially during a hyperpolarizing voltage step. The speed of inactivation was directly proportional to the hyperpolarization from the holding potential; at 60 mV the rate constant was about 0.01 msec(-1).3. An exponential fall in chloride current during the voltage pulse also occurred at pH 7.4; the speed of inactivation, which was proportional to the membrane potential, was about 20% greater at neutral than at alkaline pH values.4. The instantaneous voltage-current relation was approximately linear at pH 7.4 and 9.8; the instantaneous conductance was always greater at the alkaline pH value.5. At neutral pH values when there were no time-dependent conductance changes the voltage-current relation was linear.6. In acid solutions (pH 5.0) the chloride current gradually increased during a hyperpolarizing voltage step. The time course of this increase was complex, but it took place at greater speed during large voltage steps.7. Comparison of the steady-state voltage-current relations measured in the absence and presence of chloride ions confirmed that in alkaline solutions the chloride current could reach a limiting value.8. The equilibrium potential for the time-dependent conductance changes was close to the holding potential.