Two components of voltage-dependent calcium influx in mouse neuroblastoma cells. Measurement with arsenazo III.
N1E-115 mouse neuroblastoma cells were injected with the calcium indicator dye arsenazo III. Optical absorbance changes during voltage-clamp depolarization were used to examine the properties of the two calcium currents present in these cells. The rapidly inactivating calcium current (Moolenar and Spector, 1979b, Journal of Physiology, 292:307-323) inactivates by a voltage-dependent mechanism. The slowly inactivating calcium current is dominant in raising intracellular calcium during depolarizations to greater than -20 mV. Lowering the extracellular calcium concentration affects the two calcium currents unequally, with the slowly inactivating current being reduced more. Intracellular calcium falls very slowly (tau greater than 1 min) after a depolarization. The rapidly inactivating calcium current is responsible for a calcium action potential under physiological conditions. In contrast, it is unlikely that the slowly inactivating calcium current has an important electrical role. Rather, its function may be to add a further increment of calcium influx over and above the calcium influx through the rapidly inactivating calcium channels.
D000818:Animals; D001150:Arsenazo III; D001391:Azo Compounds; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003035:Cobalt / Q000378:metabolism / Q000494:pharmacology; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism* / Q000503:physiopathology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000378:metabolism / Q000494:pharmacology
D001391:Azo Compounds; D013757:Tetraethylammonium Compounds; D001150:Arsenazo III; D003035:Cobalt; D019789:Tetraethylammonium; C018021:cobaltous chloride; D002118:Calcium