DIHYDROPYRIDINE-SENSITIVE CALCIUM CHANNELS IN ACUTELY-DISSOCIATED HIPPOCAMPAL CA1 NEURONS

The actions of a dihydropyridine agonist (Bay K 8644) and antagonist ( nimodipine) were studied using acutely dissociated hippocampal CA1 neu rons taken from young adult guinea pigs. Under whole-cell voltage-clam p conditions, these cells exhibited a single type of calcium current, which displayed peak activation at around -10 mV and which underwent l ittle inactivation during a 100 ms depolarization. The calcium current was reversibly reduced by 10 mu M nimodipine to approximately 75% of control during a step from a holding potential of -80 mV to -10 mV. Un der similar conditions, 10 mu M Bay K 8644 reversibly increased the cu rrent to about 150% of control. Nimodipine did not alter activation an d inactivation kinetics, but Bay K 8644 caused a hyperpolarized shift of both the activation and inactivation of the calcium current. The di rect effect of nimodipine on hippocampal CAI neurons is consistent wit h previous data suggesting that nimodipine blocks calcium currents in central neurons and supports the hypothesis that these actions may und erlie the drug's ability to improve learning.