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‐sensitiv 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 neurous. Concentrations of 10 nM‐1:0 μM intrendipine reduced but did not eliminate calcium spike as measured by the rate of rise. These results were obtained at either 22° rate of rise (Dv/Dt) in 4‐week‐old cultured mouse dorsal root ganglion neurous. Concentrations of 10 nM‐1:0 μM intrendipine reduced but did not eliminate calcium spike as measured by the rate of rise. These results were obtained at either 22° or 37°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 μM tetrodotoxin (TTX), 1.8 mM calcium, and 1 μM 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.