Action of organic antagonists on neuronal calcium currents.

The low-voltage activated, fast inactivating calcium (Ca) conductance recently found in dorsal root ganglion cells is largely inert to the Ca agonist and antagonists (BAY K 8644, nifedipine and verapamil). The ubiquitous, slowly inactivating Ca conductance is strongly depressed by verapamil (20 to 100 X 10(-6) M) and with [Ca]o greater than or equal to 2 mM also by BAY K 8644, while nifedipine was weakly agonistic or ineffective in a comparable range of drug concentrations (10(-9) to 5 X 10(-7 M). The difference in affinity to verapamil renders possible a pharmacological separation of the two channels.