Cation channels in basolateral membranes of sheep parotid secretory cells.
We observed 240-pS K+ channels in 63% of cell-attached patches, and 30-pS K+ channels were observed in 95% of cell-attached patches. The 240-pS K+ channel had the relative permeability sequence of K+ (1) = Rb+ (1) > Cs+ (0.3) >> Na+ (0.03) and the relative conductance sequence of K+ (1) > Rb+ (0.22) > Cs+ (0.05) > Na+ (0). It was activated by intracellular free Ca2+ and by depolarization. It was blocked by 10 mmol/l tetraethylammonium (TEA) applied extracellularly. The 30-pS K+ channel had the relative permeability sequence of K+ (1) = Rb+ (1) > Cs+ (> Na+ (< 0.09) and the relative conductance sequence of K+ (1) > Rb+ (0.45) > Cs+ (0) = Na+ (0). Its activity was not sensitive to cytosolic free Ca2+ or membrane potential, and it was not blocked by 10 mmol/l TEA extracellularly. Acetylcholine (10 mumol/l) activated the 240-pS voltage-activated and Ca(2+)-activated K+ channels but did not activate the 30-pS K+ channels. We conclude that the 30-pS K+ channel probably determines the properties of the basolateral membrane in unstimulated sheep parotid secretory cells, whereas the 240-pS voltage-activated and Ca(2+)-activated K+ channel may be important during parasympathomimetic stimulation.
D000818:Animals; D002412:Cations / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004553:Electric Conductivity; D007473:Ion Channels / Q000378:metabolism* / Q000502:physiology; D009116:Muscarine / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000378:metabolism*; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D012756:Sheep
D002412:Cations; D007473:Ion Channels; D015221:Potassium Channels; D009116:Muscarine