Dependence upon external calcium for contractile activity in two molluscan proboscis muscles.
1. Both the radular sac and odontophore retractor muscles of Buccinum undatum depend upon [Ca]0 to raise the [Ca]i concentration of the contractile system to activation level. 2. The K-induced responses of the muscles depend mainly upon [Ca]0 for activator Ca while the ACh responses depend upon [Ca]0 to raise stored intracellular Ca to activation levels. 3. In the radular sac muscle, it is probable that the inward current is carried by Na+ or is Na(+)-dependent and this current may release [Ca]i for contraction since the muscle became spontaneously active during ACh- and K-contractures in Ca-free seawater containing 2 mM EGTA as a calcium chelator. 4. It is proposed that since calcium antagonists are more inhibitory on ACh responses than on K-contractures, ACh releases the activator calcium for the contractile system through a slow-type Ca channel while high K releases Ca through a fast-type calcium channel in these muscles.
Alohan
F I
FI
Division of Biological Sciences, University of Lancaster.
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D008974:Mollusca; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology
D002121:Calcium Channel Blockers; D000001:Calcimycin; D004110:Diltiazem; D009543:Nifedipine; D002118:Calcium