Sodium nitroprusside, a NO donor, modifies Ca2+ transport and mechanical properties in frog skeletal muscle.
Recently it has been hypothesized that, in skeletal muscle, NO produced directly by high-frequency stimulation could produce contraction through reactions with thiol groups on the sarcoplasmic reticulum (SR). However, a possible cGMP-mediated relaxing effect, similar to that seen in smooth muscle, has also been demonstrated. We used purified SR preparations and single fibres from frog fast muscles incubated with different concentrations of sodium nitroprusside (SNP) in this study. The results obtained from a long low-frequency stimulation, together with those from a study on Ca2+ transport regulation, showed that the presence of NO precursor induced: an acceleration of the onset of fatigue in single fibres; a decreased vesicular Ca2+ content due to increased Ca2+ release; a shift to open status in SR Ca2+ channels; an increase in SR Ca2+ pump activity. The data presented in this paper seem to indicate that the increased NO in the muscle fibres can influence muscle activity in different ways, perhaps depending on the metabolic status of the muscle and target (filaments, sarcolemma, SR) with which the NO (or its derivatives) acts.
Belia
S
S
Dipartimento di Biologia Cellulare e Molecolare-Sezione di Fisiologia e Biofisica, Università di Perugia, Italy.
Pietrangelo
T
T
Fulle
S
S
Menchetti
G
G
Cecchini
E
E
Felaco
M
M
Vecchiet
J
J
Fanò
G
G
D000818:Animals; D001001:Anura; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000493:pharmacokinetics*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D003995:Dibutyryl Cyclic GMP / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D018715:Microscopy, Video; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000166:cytology; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology*; D012433:Ryanodine / Q000378:metabolism / Q000494:pharmacology; D013314:Stress, Mechanical; D013439:Sulfhydryl Reagents / Q000494:pharmacology*; D014316:Tritium
D020030:Nitric Oxide Donors; D013439:Sulfhydryl Reagents; D014316:Tritium; D012433:Ryanodine; D009599:Nitroprusside; D009569:Nitric Oxide; D003995:Dibutyryl Cyclic GMP; D009252:NADPH Dehydrogenase; D006162:Guanylate Cyclase; D000252:Calcium-Transporting ATPases; D002118:Calcium