Brief increases in intracellular Ca2+ activate K+ current and non-selective cation current in rat nucleus basalis neurons.

Neurons were acutely dissociated from the rat nucleus basalis, and membrane currents (whole-cell patch-clamp) and intracellular free Ca2+ concentrations (Fura-2) were measured simultaneously from large neurons (approximately 25 microns in diameter). A brief depolarization from -60 to 0 mV for 200 ms evoked an increase in intracellular free calcium and a slow outward tail current (72 +/- 8 pA, n = 30). The outward current reversed polarity at -75.5 +/- 2.7 mV (n = 14). The tail current declined and the intracellular calcium recovered its resting level exponentially with time-constants of 1.0 +/- 0.1 s and 2.5 +/- 0.2 s, 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 +/- 8 pA, n = 44). The inward tail current reversed polarity at -27.8 +/- 3.8 mV (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.