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.
Tatsumi
H
H
Department of Autonomic Physiology, Tokyo Medical and Dental University, Japan.
Katayama
Y
Y
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001479:Basal Ganglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000502:physiology*; D002586:Cesium / Q000494:pharmacology; D016257:Fura-2; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D013050:Spectrometry, Fluorescence
D007473:Ion Channels; D015221:Potassium Channels; D002586:Cesium; D012964:Sodium; D002118:Calcium; D016257:Fura-2