Effects of nitrendipine on the voltage-sensitive calcium channel in mammalian sensory neurons.

We examined the ability of nitrendipine, a calcium antagonist believed to block the voltage-sensitive calcium channels in a number of excitable membranes, to affect the calcium spike duration and rate of rise (Dv/Dt) in 4-week-old cultured mouse dorsal root ganglion neurons. Concentrations of 10 nM-1.0 microM nitrendipine reduced but did not eliminate calcium spike as measured by the rate of rise. These results were obtained at either 22 degrees or 37 degrees C in solutions containing 5 mM calcium. A similar lack of total block was seen with prolonged incubation in sodium-free recording media containing 1 microM tetrodotoxin (TTX), 1.8 mM calcium, and 1 microM nitrendipine. Calcium spike duration was affected in an inconsistent manner by nitrendipine and other 1,4 dihydropyridines. Cobalt (10 mM) totally blocked the voltage-dependent calcium mechanism as measured by either the spike duration or the rate of rise. We conclude that calcium influx through the voltage-sensitive calcium channel in mouse dorsal root ganglion neurons is not blocked by even high concentrations of nitrendipine.