Multiple actions of Bay K 8644 on high-threshold Ca channels in adult rat sensory neurons

omega-Conotoxin (omega-CgTx, 6.4 microM) failed to fully block the high-threshold Ba currents (HVA; L,N) of adult rat sensory neurons, and showed only a minor inhibitory action on the low-voltage activated current (LVA,T). In most of the CgTx-treated neurons the residual high-threshold Ba current was strongly agonized by the 1,4-dihydropyridine Bay K 8644. 1 microM Bay K 8644 enhanced 3- to 4-fold the size of this current at low membrane potentials and prolonged its deactivation kinetics by one order of magnitude. As in cardiac cells, in some neurons Bay K 8644 sped up about 3-fold the inactivation time course of the omega-CgTx-resistant Ba current, suggesting multiple actions of the dihydropyridine on neuronal high-threshold Ca channels.