Comparison of Mg, Mn, and Co ions affecting the beta-adrenoceptor-mediated membrane response in the guinea-pig taenia caeci.
Electrical activity was recorded intracellularly from the muscle cell of guinea-pig taenia caeci in Locke solution. Membrane potential was -46.4 mV, and spike potentials were discharged spontaneously. Isoprenaline (3 microM) hyperpolarized the membrane and suppressed the spike discharge. The hyperpolarization by isoprenaline was increased at low K (2 mM), while decreased at high K (11.8, 29.5, 59 mM). The hyperpolarization by isoprenaline was potentiated in the presence of external Mg ions, depending on the concentration of Mg (0-9.6 mM). Forskolin (3 microM) and papaverine (30 microM) hyperpolarized the membrane; the effects were augmented by 1.2 mM Mg. The hyperpolarization in response to 3 microM isoprenaline or 100 microM papaverine was inhibited by Mn, Co, and low Ca (1 mM) whereas it was not affected by high Ca (7.5 mM). Verapamil (0.5, 2 microM) had no influence of the hyperpolarization caused by isoprenaline. It was discussed that extracellular and/or intracellular Mg and Ca ions played important roles in the beta-adrenoceptor-mediated action on the smooth muscle membrane of taenia caeci.
Maruta
K
K
Department of Physiology, Yamaguchi University School of Medicine, Ube, Japan.
Osa
T
T
Inoue
H
H
D000818:Animals; D002432:Cecum / Q000187:drug effects / Q000502:physiology*; D003035:Cobalt / Q000494:pharmacology*; D005576:Colforsin / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D010208:Papaverine / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*
D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D003035:Cobalt; D008345:Manganese; D010208:Papaverine; D008274:Magnesium; D007545:Isoproterenol