Asymmetric intramembrane charge movement in mouse hippocampal pyramidal cells

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Intramembrane charge movement was recorded from freshly dissociated hippocampal pyramidal cells from mice using the whole cell clamp technique. 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 pulse. The amount of charge displaced at the onset of the pulse ( Q on) was equivalent to the charge moved at repolarization ( Q off). The relationship 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 membrane 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/μF, V 1 2 was 1.70 ± 2.90 mV, and k was 18.80 ± 1.20 mV ( n = 16). Phenylglyoxal (10 mM), an arginine modifying reagent, reduced the maximum amount of charge movement to 14% of control. The inhibitory effect of phenylglyoxal was time dependent and the decline time course of maximum amount of charge movement could be fitted by a single exponential curve with a time constant of 5.79 min. The dihydropyridine (DHP) receptor antagonist, nifedipine, immobilized 54% of the charge movement. These results suggest that a part of the charge movement reflects the conformational change of the DHP receptors upon membrane depolarization.