ASYMMETRIC INTRAMEMBRANE CHARGE MOVEMENT IN MOUSE HIPPOCAMPAL PYRAMIDAL CELLS

Intramembrane charge movement was recorded from freshly dissociated hi ppocampal pyramidal cells from mice using the whole cell clamp techniq ue. Once the ionic currents were suppressed, a depolarizing pulse from a holding potential of -80 mV elicited a capacitive transient outward current at onset and a capacitive inward current at offset of the pul se. The amount of charge displaced at the onset of the pulse (Q(on)) w as equivalent to the charge moved at repolarization (Q(off)). The rela tionship between the amount of charge moved and pulse potential could be expressed by a simple two states Boltzmann equation: Q = Q(max)/{1 + exp[-(V-V-1/2)/k]}, where Q(max) is the maximum charge, V-1/2 the me mbrane potential at which Q is half of Q(max) and k is a slope factor. On average, Q(max) was 10.90 +/- 0.62 nC/mu F, V-1/2 was 1.70 +/- 2.9 0 mV, and k was 18.80 +/- 1.20 mV (n = 16). Phenylglyoxal (10 mM), an arginine modifying reagent, reduced the maximum amount of charge movem ent to 14% of control. The inhibitory effect of phenylglyoxal was time dependent and the decline time course of maximum amount of charge mov ement could be fitted by a single exponential curve with a time consta nt of 5.79 min. The dihydropyridine (DHP) receptor antagonist, nifedip ine, immobilized 54% of the charge movement. These results suggest tha t a part of the charge movement reflects the conformational change of the DHP receptors upon membrane depolarization.