title: Voltage-dependent K+ currents and underlying single K+ channels in pheochromocytoma cells.
abstract: Properties of the whole-cell K+ currents and voltage-dependent activation and inactivation properties of single K+ channels in clonal pheochromocytoma (PC-12) cells were studied using the patch-clamp recording technique. Depolarizing pulses elicited slowly inactivating whole-cell K+ currents, which were blocked by external application of tetraethylammonium+, 4-aminopyridine, and quinidine. The amplitudes and time courses of these K+ currents were largely independent of the prepulse voltage. Although pharmacological agents and manipulation of the voltage-clamp pulse protocol failed to reveal any additional separable whole-cell currents in a majority of the cells examined, single-channel recordings showed that, in addition to the large Ca++-dependent K+ channels described previously in many other preparations, PC-12 cells had at least four distinct types of K+ channels activated by depolarization. These four types of K+ channels differed in the open-channel current-voltage relation, time course of activation and inactivation, and voltage dependence of activation and inactivation. These K+ channels were designated the Kw, Kz, Ky, and Kx channels. The typical chord conductances of these channels were 18, 12, 7, and 7 pS in the excised configuration using Na+-free saline solutions. These four types of K+ channels opened in the presence of low concentrations of internal Ca++ (1 nM). Their voltage-dependent gating properties can account for the properties of the whole-cell K+ currents in PC-12 cells.
mesh_terms: D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D018999:Charybdotoxin; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D010673:Pheochromocytoma / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011802:Quinidine / Q000494:pharmacology; D012604:Scorpion Venoms / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000631:Aminopyridines; D007473:Ion Channels; D012604:Scorpion Venoms; D013757:Tetraethylammonium Compounds; D018999:Charybdotoxin; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D011802:Quinidine; D011188:Potassium