The effect of cromakalim on intracellular [Ca2+] in isolated rat skeletal muscle during fatigue and metabolic blockade.
The effects of the ATP-sensitive K+ channel (KATP channel) opener cromakalim on excitation-contraction (E-C) coupling were studied in skeletal muscle during fatiguing and non-fatiguing activity. Intracellular calcium concentration ([Ca2+]i) was monitored using the fluorescent indicator fura-2 in isolated single skeletal muscle fibres enzymatically dissociated from rat flexor digitorum brevis. A protocol of tetanic stimulation (50 Hz for 300 ms) with progressively shorter durations between tetani was used to induce E-C coupling failure in these cells. Cromakalim (100-800 microM) had little effect on peak [Ca2+]i during twitch and non-fatiguing tetanic stimulation. However, with 0.4 s between tetani, 100 microM cromakalim decreased peak tetanic [Ca2+]i from 1.47 +/- 0.11 microM to 8.35 +/- 55 nM, but did not affect resting [Ca2+]i (control, 220 +/- 40 nM; with cromakalim, 171 +/- 33 nM). Cyanide (2 mM) decreased tetanic [Ca2+]i and increased resting [Ca2+]i during the stimulus protocol; with 0.4 s between tetani, peak [Ca2+]i was 820 +/- 50 nM and resting [Ca2+]i was 443 +/- 32 nM. The ability of cromakalim to inhibit E-C coupling was enhanced by the presence of cyanide. Complete blockade of metabolism by cyanide and iodoactetate (0.1 mM) caused a marked rise in resting [Ca2+]i and inhibition of the tetanic rise of [Ca2+]i. With cromakalim (100 microM) present, E-C coupling failed during metabolic blockade but without a significant increase in resting [Ca2+]i. These results are consistent with a role for the KATP channel in the failure of Ca2+ release during fatigue.
Burton
F L
FL
Institute of Biomedical and Life Sciences, University of Glasgow, UK.
Smith
G L
GL
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D019806:Cromakalim; D003486:Cyanides / Q000494:pharmacology; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism*; D007461:Iodoacetates / Q000494:pharmacology; D019807:Iodoacetic Acid; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009994:Osmolar Concentration; D015221:Potassium Channels / Q000187:drug effects; D011758:Pyrroles / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D001578:Benzopyrans; D003486:Cyanides; D007461:Iodoacetates; D015221:Potassium Channels; D011758:Pyrroles; D019806:Cromakalim; D000255:Adenosine Triphosphate; D002118:Calcium; D019807:Iodoacetic Acid