Abstract
BRL 34915 (4–64 × 10−7 M), isoprenaline (0.5–32 × 10−8 M) and nicorandil (4–64 × 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 × 10−3 M) and noradrenaline (1–16 × 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 × 10−7 M) and to nicorandil (64 × 10−6 M) produced an increase in the 86Rb efflux rate coefficient which was unaffected by apamin (10−7 M). Exposure to isoprenaline (32 × 10−8 M) had no effect on the 86Rb efflux rate coefficient. Exposure to noradrenaline (16 × 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.