Muscle contraction and inward current induced by silver and effect of Ca2+ channel blockers.
Single fibers from toe or anterior tibialis muscle contracted transiently and then tonically in the presence of 1.8 mM Ca2+ on addition of 10 microM Ag+. Exposure of fibers to Cd2+ completely inhibited tonic contraction and modified phasic contraction to some extent. Nifedipine at 10 microM initially potentiated and then completely inhibited twitch tension; subsequently, fibers no longer contracted phasically in response to 20 microM Ag+, whereas slight tonic contraction still occurred. Fibers with membrane potential clamped at -90 mV produced maintained inward current on application of Ag+. Simultaneous administration of 1 mM Cd2+ and 10 microM Ag+ to fibers voltage clamped with the double mannitol gap technique almost completely blocked the inward current. Removal of Cd2+ elicited a rapid and large inward current. Ag(+)-induced inward current was inhibited when 1 mM Cd2+ was applied to fibers during development of the inward current. In fibers paralyzed with 10 microM nifedipine, the inward current induced by 10 microM Ag+ was partially inhibited. These results suggest that phasic contraction induced by Ag+ is controlled by L-type Ca2+ channels (probably voltage sensors) located in the T-tubular membrane, whereas tonic contraction involves Ca2+ channels sensitive and/or insensitive to dihydropyridine in the surface and T-tubular membranes.
Department of Physiology, Nagoya City University Medical School, Japan.
T
T
Oba
T
T
Aoki
M
M
Koshita
K
K
Nihonyanagi
M
M
Yamaguchi
D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002413:Cations, Divalent; D066298:In Vitro Techniques; D008353:Mannitol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology*; D011892:Rana catesbeiana; D011898:Ranidae; D012834:Silver / Q000494:pharmacology*; D013997:Time Factors
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002413:Cations, Divalent; D002104:Cadmium; D012834:Silver; D008353:Mannitol; D009543:Nifedipine