Gold ion induces contraction in frog skeletal muscle fibers.
In Ringer solution, gold ions (Au3+) at concentrations more than 50 microM produced a phasic and subsequent tonic contraction spontaneously in single toe muscle fiber of frog. When 1.8 mM Ca2+ in Ringer solution was replaced by 3 mM Mg2+, tonic contraction was no longer provoked in response to Au3+. Only phasic contraction was potentiated by 10 mM perchlorate (an L-type Ca2+ channel activator) irrespective of external Ca2+, and both phasic and tonic contractions were blocked by 10 microM nifedipine (an L-type Ca2+ channel blocker). Upon application of 5 mM dithiothreitol to the contracting fiber, the Au(3+)-induced tension disappeared rapidly. The fiber pretreated with 0.05% H2O2 for 10 min did not respond to Au3+ with visible contraction. Treatment of H2O2-paralyzed fibers with dithiothreitol (to reduce oxidized sulfhydryl groups) fully restored the Au(3+)-induced contraction. These results suggest that the phasic contraction induced by Au3+ probably is mediated through sulfhydryl groups in the L-type Ca2+ channel (dihydropyridine receptor) on the transverse tubular membrane. Sustained contraction was produced by Ca2+ application to Au(3+)-treated fibers in Mg(2+)-Ringer solution, and Au3+ caused membrane depolarization in a dose-dependent manner. These effects of Au3+ may explain tonic contraction development.
Nihonyanagi
K
K
Department of Physiology, Nagoya City University Medical School, Japan.
Oba
T
T
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type; D004229:Dithiothreitol / Q000494:pharmacology; D004347:Drug Interactions; D006046:Gold / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009124:Muscle Proteins / Q000187:drug effects; D009132:Muscles / Q000187:drug effects*; D010472:Perchlorates / Q000494:pharmacology; D011892:Rana catesbeiana; D017670:Sodium Compounds / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D009124:Muscle Proteins; D010472:Perchlorates; D017670:Sodium Compounds; D006046:Gold; C031068:sodium perchlorate; D006861:Hydrogen Peroxide; D008274:Magnesium; D002118:Calcium; D004229:Dithiothreitol