Characteristics of the Desensitization of Glycine-Mediated Ion Currents in Frog Spinal Cord Neurons

Abstract

Whole-cell patch clamp studies of isolated spinal cord neurons from the frog Rana temporaria in voltage-clamped conditions addressed the kinetics of ion channel desensitization evoked by glycine application. The ion current desensitization phase (decay from 90% to 10%), induced by periodic applications of glycine (1 mM), approximated an exponential function. Approximation results identified three types of glycine-mediated response. The decay constant of type 1 responses in the first minute of the experiment was τ1 = 1693 ± 135 msec (n = 8) and decreased from application to application during further recording. Type 2 responses had a decay constant τ2 = 364 ± 42 msec (n = 9) at the beginning of recording and showed virtually no change with time. Type 3 responses had a biexponential decay consisting of a rapid (τ2) component and a slow (τ1) component, acceleration of the desensitization phase of this response from application to application occurring as a result of a decrease in the larger decay constant τ1. These data suggest that the frog spinal cord membrane has at least two varieties of glycine receptor with different rates of desensitization and different dynamics of changes in properties during patch-clamp recording. Different neurons can evidently have these receptor varieties simultaneously or separately.