Effect of apamin on responses to BRL 34915, nicorandil and other relaxants in the guinea-pig taenia caeci.
BRL 34915 (4-64 X 10(-7) M), isoprenaline (0.5-32 X 10(-8) M) and nicorandil (4-64 X 10(-6) M) produced a slowly-developing relaxation of spontaneous tone of the guinea-pig taenia caeci; with no after-contraction on washout. These inhibitory responses were unaffected by apamin (10(-7) M). Adenosine triphosphate (0.06-2 X 10(-3) M) and noradrenaline (1-16 X 10(-7) M) produced a rapid inhibition of spontaneous tone with a prominent after-contraction, especially on washout. Both the inhibitory effect and the rebound contraction were abolished by apamin (10(-7) M). Exposure to both BRL 34915 (64 X 10(-7) M) and to nicorandil (64 X 10(-6) M) produced an increase in the 86Rb efflux rate coefficient which was unaffected by apamin (10(-7) M). Exposure to isoprenaline (32 X 10(-8) M) had no effect on the 86Rb efflux rate coefficient. Exposure to noradrenaline (16 X 10(-7) M) produced an increase in the 86Rb efflux rate coefficient which was abolished by apamin (10(-7) M). The results confirm that both BRL 34915 and nicorandil are capable of opening potassium channels in smooth muscle but show that the channel is not apamin-sensitive.
Weir
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Weston
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D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001030:Apamin / Q000494:pharmacology*; D001514:Bee Venoms / Q000494:pharmacology*; D001578:Benzopyrans / Q000494:pharmacology*; D002432:Cecum / Q000187:drug effects; D019806:Cromakalim; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009125:Muscle Relaxants, Central / Q000494:pharmacology*; D009129:Muscle Tonus / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009536:Niacinamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D020108:Nicorandil; D009638:Norepinephrine / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology*
D000959:Antihypertensive Agents; D001514:Bee Venoms; D001578:Benzopyrans; D007473:Ion Channels; D009125:Muscle Relaxants, Central; D011758:Pyrroles; D019806:Cromakalim; D001030:Apamin; D009536:Niacinamide; D020108:Nicorandil; D000255:Adenosine Triphosphate; D007545:Isoproterenol; D009638:Norepinephrine