Mechanism of carbachol-evoked contractions of guinea-pig ileal smooth muscle close to freezing point.

摘要

1. The effect of lowering the temperature to near freezing-point upon the contractions and [3H]-inositol phosphate responses to carbachol were investigated in longitudinal smooth muscle from the guinea-pig ileum. 2. The peak amplitude of the contraction to a single application of 100 microM carbachol was the same at 37 degrees C and temperatures near freezing-point. However, the sensitivity to carbachol was reduced upon lowering the temperature and the time to peak contraction was increased from 5-10 s to 2-10 min. Even when the temperature was maintained near freezing-point, washing off carbachol produced a relaxation and eventual return of tension to basal levels. 3. Incubating the tissue in 140 mM K+, calcium-free solution or in calcium channel antagonists significantly reduced the carbachol-induced contraction to 10-30% of the control at 37 degrees C and also at 3 degrees C. Thus the majority of the activator calcium required for contraction entered the tissue via voltage-dependent calcium channels (VDCs) at both 37 degrees C and 3 degrees C. 4. The contractions produced by high potassium solutions were less at temperatures close to freezing-point than those at 37 degrees C suggesting that voltage-dependent calcium entry was inhibited as the temperature was lowered. 5. A small part of the contractile response to 100 microM carbachol was resistant to the removal of extracellular calcium at both 37 degrees C and 3 degrees C and this component was increased under depolarizing conditions.(ABSTRACT TRUNCATED AT 250 WORDS)