Brief increases in intracellular Ca 2+ activate K + current and non-selective cation current in rat nucleus basalis neurons

Abstract

Neurons were acutely dissociated from the rat nucleus basalis, and membrane currents (whole-cell patch-clamp) and intracellular free Ca 2+ concentrations (Fura-2) were measured simultaneously from large neurons (approximately 25 μm in diameter). A brief depolarization from −60 to 0 mV for 200ms evoked an increase in intracellular free calcium and a slow outward tail current (72 ± 8pA, n = 30). The outward current reversed polarity at −75.5 ± 2.7mV ( n = 14). The tail current declined and the intracellular calcium recovered its resting level exponentially with time-constants of 1.0 ± 0.1s and 2.5 ± 0.2s, respectively ( n = 17). In neurons loaded with Cs-gluconate, a similar depolarizing pulse evoked a similar increase in intracellular free calcium, but this was now followed by an inward tail current ( 118 ± 8pA, n = 44). The inward tail current reversed polarity at −27.8 ± 3.8mV (n = 7), and was suppressed by removal of external sodium ions. Neither outward nor inward tail currents were observed, when the external solution was calcium-free or when the pipette solution contained EGTA (10 mM). These results indicate that a depolarization causes a calcium entry and that this consequently increases both K + conductance and non-selective cation conductance.