Delayed contractures induced by external cadmium ions in rat soleus muscle fibres.
Cd(2+)-induced contractures began with a delay of approximately =4 min after adding 3 mM Cd2+ to external solutions that contained Cl- as the major anion. Tension increased to approximately =20% of peak tetanic tension after 30 min and was maintained after Cd2+ washout. Tension developed more rapidly at higher [Cd2+] (up to 10 mM). There was a lack of correlation between the delay before the contracture and contracture tension: (1) tension was reduced by 2 mM CO2+ or 50 microM nifedipine, although the delay remained at approximately =4 min, and (2) the delay fell to seconds when Cd2+ was added in SO42- solutions, although tension was the same as in Cl- solutions. Since (SO4)2- solutions swell T-tubules, Cd2+ may enter the T-system before inducing contractures. Cd(2+)-induced contractures depended on external [Ca2+] since they were reduced when Ca2+ was omitted from solutions. The contractures did not depend on activation of excitation-contraction coupling, since tension was not altered when the voltage sensor was inactivated by depolarization in 40 mM K+. A small contracture developed with 3 mM Zn2+, but not 3 mM Co2+ or La3+. Both Cd2+ and Zn2+ activated the contractile proteins in skinned fibres. Cd(2+)-induced contractures may depend on external Cd2+ releasing Ca2+ from the sarcoplasmic reticulum (SR), or on Cd2+ entering the fibre, releasing Ca2+ from the SR and/or directly activating the contractile proteins.
Mould
J
J
Muscle Research Group, Division of Biochemistry and Molecular Biology, John Curtin School of Medical Research, Australian National University, Canberra City, ACT, Australia.
Dulhunty
A F
AF
D000818:Animals; D002104:Cadmium / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D003285:Contractile Proteins / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors; D015032:Zinc / Q000378:metabolism
D002121:Calcium Channel Blockers; D003285:Contractile Proteins; D004791:Enzyme Inhibitors; D019831:Sodium-Calcium Exchanger; D002104:Cadmium; D000252:Calcium-Transporting ATPases; D009543:Nifedipine; D015032:Zinc; D002118:Calcium