Excitation-contraction coupling without Ca2+ action potentials in small intestine.
Sensitive mechanical and intracellular electrical recordings showed that phasic contractions occurred in response to electrical slow waves in the absence of Ca2+ action potentials. Drugs that either enhanced or depressed slow waves were used to study the relationship between slow-wave amplitude and the amplitude of the phasic contractions. Acetylcholine (Ach) (10(-8) to 3 X 10(-7) M) increased slow waves and contractions without causing action potentials. When ACh was raised to 10(-6) M, action potentials were elicited and accompanying contractions increased in amplitude by at least a factor of five. The Ca2+ channel blocker, Mn2+ (0.5 mM), decreased slow-wave amplitude and the associated phasic contractions. These data agree with a previous study (12), suggesting that an oscillation in intracellular Ca2+ occurs during each slow-wave cycle. The present study suggests that the increase in intracellular Ca2+ during the slow wave is sufficient to activate the contractile apparatus.
D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004285:Dogs; D005260:Female; D007082:Ileum / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008345:Manganese / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*
D008345:Manganese; D000109:Acetylcholine; D002118:Calcium