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Block of calcium-activated potassium channels in mammalian arterial myocytes by tetraethylammonium ions.
Langton P, Nelson MT, Huang Y, Standen N
American Journal of Physiology-Heart and Circulatory Physiology. 1991;260( 3 Pt 2):H927-34.
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Abstract
The effects of tetraethylammonium ions (TEA+) and tetrapentylammonium ions (TPeA+) on Ca2(+) -activated K+ (KCa) channels were studied in membrane patches from mesenteric arterial myocytes. External TEA+ produced a flickery block. The concentration dependence for reduction in mean unitary current was consistent with 1:1 binding, with dissociation constants (Kd) in rat and rabbit of 196 and 159 microM at 0 mV, and the block was weakly voltage dependent. Rate constants for blocking and unblocking were 380 mM-1.ms-1 and 73 ms-1, respectively. In patches containing several channels TEA+ reduced average current to the same extent as mean unitary current, implying that TEA+ block is independent of the channel state. Block was unaffected by raising external K+ to 120 mM. External TPeA+ blocked with slower kinetics and lower affinity than TEA+ (Kd, 1.49 mM). The sulfonylurea glibenclamide (10-100 microM), the hyperpolarizing vasodilator cromakalim (5 microM), and internal ATP (1 mM) were without effect on channel activity. We conclude that TEA+ is a relatively effective blocker of single KCa channels of arterial smooth muscle and should block macroscopic currents equally well, whereas external TPeA+ is about eight times less effective.
Keyword(s)
Animals; Cromakalim; Electrophysiology; Ions; Kinetics; Tetraethylammonium; antagonists & inhibitors: Potassium; cytology: Arteries; drug effects: Potassium Channels; pharmacology: Adenosine Triphosphate; pharmacology: Benzopyrans; pharmacology: Calcium; pharmacology: Glyburide; pharmacology: Pyrroles; pharmacology: Quaternary Ammonium Compounds; pharmacology: Tetraethylammonium Compounds