Calcium currents in freshly dissociated rat Purkinje and dorsal root ganglion cells

Whole-cell patch clamp recording was used to characterize calcium currents in cerebellar Purkinje cells dissociated from one- to three-week postnatal rats. A subset of cells had a low-threshold, transient current similar to the T-type current in peripheral neurons. All Purkinje cells had a high-threshold, slowly-inactivating current. Only a small component of the slowly-inactivating current was sensitive to dihydropyridine antagonists or the dihydropyridine agonist BAY K8644. w-Conotoxin had little effect on the slowly-inactivating current. Purkinje cells thus appear to have three types of calcium channels: T-type channels, dihydropyridine-sensitive L-type channels, and a predominant type of high-threshold, slowly-inactivating channel that is pharmacologically distinct from the L- and N-type channels characterized in peripheral neurons.; Recordings were then made from dissociated rat dorsal root ganglion (DRG) neurons to see whether they also have a dihydropyridine- and w-conotoxin-resistant high-threshold calcium current neurons (chick DRG cells do not appear to have such a current). Approximately one-third of the total high-threshold current in rat DRG neurons remained in the presence of saturating concentrations of nitrendipine and w-conotoxin. Many properties of the resistant current were similar (but not identical) to those of the w-conotoxin-sensitive current, including its rate of inactivation, voltage-dependence of activation, and rate of deactivation. The dihydropyridine- and w-conotoxin-resistant current in DRG neurons does not appear to be identical to the Purkinje cell slowly-inactivating current. It appears likely that there are many types of high-threshold calcium currents in rat neurons that differ only subtly in their voltage-dependent properties.