Heterogeneity of the effects of monensin on two types of contractions evoked by inhibition of Na+-K+ ATPase in the guinea-pig vas deferens.
The interactions between ouabain or K+-free medium and monensin on noradrenaline (NA) release and Ca2+-evoked contractions were assessed in guinea-pig vas deferens. Ouabain (10 microM) produced large, sustained contractions and monensin (1 microM) small, transient contractions. The ouabain-evoked contraction tended to be potentiated in the presence of monensin. The marked contraction induced by ouabain plus monensin was nearly abolished by phentolamine or by treatment with 6-hydroxydopamine. Ouabain caused the release of NA from the tissue, as determined in an HPCL-ECD study. This ouabain-evoked release of NA was enhanced by the simultaneous administration of monensin. High Ca2+ (10 mM) per se, ouabain, monensin or K+-free medium did not elicit contraction of the tissue in the presence of phentolamine. However, 10 mM Ca2+ caused a large contraction 45-65 min after exposure to ouabain or K+-free medium and this contraction was suppressed by monensin. The contraction evoked by Ca2+ in the presence of ouabain was further inhibited by amiloride, an inhibitor of Na+-Ca2+ or Na+-H+ exchange transport, but not by nifedipine, a voltage-dependent Ca2+ antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)
Katsuragi
T
T
Department of Pharmacology, School of Medicine, Fukuoka University, Japan.
Kuratomi
L
L
Tokunaga
T
T
Furukawa
T
T
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D006168:Guinea Pigs; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008985:Monensin / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014649:Vas Deferens / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology
D007476:Ionophores; D010042:Ouabain; D000584:Amiloride; D008985:Monensin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine; D010646:Phentolamine