A voltage-clamp study of calcium currents in neurons freshly isolated from the dorsal root ganglion of adult rats.

Calcium currents were studied in a preparation of freshly isolated neurons of the dorsal root ganglion (DRG) of adult rats using the whole-cell voltage-clamp technique in conditions of minimal current flow through sodium and potassium channels. A low-threshold (LT) and a high-threshold (HT) current were distinguished on the basis of a different potential of activation. Both currents also showed differences in their peak amplitude, their distribution among the cells, their kinetics, their steady-state inactivation curve and their sensitivity to cadmium. Comparison of the properties of both currents with the known properties of calcium currents in DRG neurons from immature animals indicates a slower rate of inactivation of the LT-current in the adult DRG neuron. The calcium entry blocker flunarizine (10 microM) caused a negative shift of the steady-state inactivation curve of the inactivating component of HT-current, an effect which suggests voltage-dependent inhibition.