Elevations in rat soleus muscle [Ca2+] with passive stretch.
Previous work has demonstrated that muscular injury in rat soleus muscles resulting from eccentric contractions (downhill walking) is accompanied by elevations in mitochondrial [Ca2+] (MCC). Muscles are stretched during eccentric contractions, and there is evidence in the literature that stretch of the cell membrane induces Ca2+ influx in various tissues, including skeletal muscle. The purpose of this study was to determine if passive stretch of rat soleus muscles will induce increases in total muscle [Ca2+] (TCC) and MCC. Soleus muscles from female rats (51-122 g) were isolated and incubated in vitro for 2 h at resting length (Lo) or at the maximal in situ length (S). TCC (+62%) and MCC (+56%) were elevated in the S muscles. Also, there was a 63% reduction in maximal twitch tension in the S muscles. ATP concentration, phosphocreatine concentration, and lactate release between Lo and S muscles were the same, indicating that impaired metabolism was not responsible for the observed differences in [Ca2+] and force production between Lo and S muscles. Increases in TCC in the S condition indicate that stretch results in Ca2+ influx from the extracellular space, which is supported by the observation that when S muscles were incubated in Ca(2+)-free buffer, TCC and MCC did not increase. High concentrations of verapamil (0.25-0.75 mM) blocked the elevations in TCC and MCC in the S muscles, but the magnitude of the drug concentration required makes it questionable whether the effect resulted from specific blockade of slow voltage-sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)
Armstrong
R B
RB
Exercise Biochemistry Laboratory, University of Georgia, Athens 30602.
Duan
C
C
Delp
M D
MD
Hayes
D A
DA
Glenn
G M
GM
Allen
G D
GD
D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D003402:Creatine Kinase / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D008931:Mitochondria, Muscle / Q000187:drug effects / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000187:drug effects / Q000293:injuries / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D014700:Verapamil; D003402:Creatine Kinase; D002118:Calcium