Effects of ouabain and EGTA on the inhibitory effect of Ca2+ on guinea pig stomach smooth muscle ('Ca reversal').
Guinea pig stomach smooth muscle is known to show sustained contraction when treated with carbachol (CCh) in Ca-free solution containing 2 X 10(-3) M EGTA ('Ca-free contraction'). After pretreatment of the muscle with a Ca antagonist (D-600, nicardipine or nifedipine), addition of 10(-4) M Ca2+ (pCa 4.0) relaxed this CCh-induced Ca-free contraction ('Ca reversal'), but without pretreatment with a Ca antagonist, Ca2+ evoked contraction. In a Ca buffer containing 2 X 10(-3) M EGTA, low concentrations of Ca2+, 10(-8)-3 X 10(-7) M (pCa 8.0-6.5), relaxed the Ca-free contraction dose dependently ('Ca reversal'), whereas concentrations higher than 10(-6) M Ca2+ (pCa 6.0-) reversed this relaxation back to contraction. EGTA at 5 X 10(-3) or 10(-2) M potentiated the Ca reversal, whereas no reversal occurred in a Ca buffer containing 10(-3) M EGTA. This Ca reversal was inhibited in K(+)-depleted, Ca-free solution and by ouabain in Ca buffer containing EGTA (5 X 10(-3) or 10(-2) M). These results show that Ca reversal of guinea pig stomach smooth muscle occurs at low concentrations of Ca2+ and that its mechanism is related to ouabain-sensitive processes, such as the function of Na(+)-K+ ATPase.
Karibe
H
H
Department of Molecular Pharmacology, Meiji College of Pharmacy, Tokyo, Japan.
Uchida
M K
MK
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers; D002217:Carbachol / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology*; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000201:enzymology; D010042:Ouabain / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013270:Stomach / Q000187:drug effects
D002121:Calcium Channel Blockers; D004533:Egtazic Acid; D010042:Ouabain; D002217:Carbachol; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium