NIFEDIPINE-SENSITIVE INTRAMEMBRANE CHARGE MOVEMENT IN PURKINJE-CELLS FROM MOUSE CEREBELLUM

1. The intramembrane charge movement was recorded in freshly dissociat ed Purkinje cells from 14- to 18-day-old mouse cerebellum using the wh ole-cell voltage damp technique. 2. After pharmacological elimination of all ionic currents, a depolarizing pulse from a holding potential o f -80 mV revealed a transient capacitive outward current at the onset and a transient inward current at the end of the pulse. The amount of charge transferred at the onset (Q(on)) was equivalent to that mo fied at the end of the pulse (Q(off)). The decay time course of Q(on) can be fitted by a single exponential curve with a maximum time constant o f 1.89 +/- 0.35 ms at 20 mV (n = 11). 3. The charge movement had an S- shaped dependence on test membrane potential, according to a two-state Boltzmann function. The maximum amount (Q(max)) of Q(on) that could b e moved was 17 48 +/- 0 83 nC mu F-1; the membrane potential at which half the charge movement occurred ((V) over bar) was 13.48 +/- 2.20 mV and the slope factor (k) was 16.83 +/- 0.84 mV (n = 27). 4. Phenylgly oxal (2 mM), an arginine-specific modifying reagent, reduced Q(max) to 60% of control after 20 min treatment. 5. The charge movement aias pa rtially immobilized by nifedipine in a dose-dependent manner with an I C50 of 70 nM. The fraction of tile nifedipine-sensitive component was 39% of tile total charge movement. The potential dependence of the nif edipine-sensitive charge movement could be expressed by a Boltzmann fu nction with values of 7.00 +/- 0.53 nC mu F-4 for Q(max), 31.44 +/- 4. 23 mV for (V) over bar and 21.53 +/- 3.18 mV for k (n = 8). 6. The P-t ype calcium channel specific inhibitor, omega-Aga IVA (250 nM), had no effect on intramembrane charge movement. 7. The above results show th at part of tile intramembrane charge movement in Purkinje cells may be related to a conformational change of DHP receptors upon membrane dep olarization.