Ischemia/reperfusion-induced changes in intracellular free Ca2+ levels in rat skeletal muscle fibers - an in vivo study

Accumulation of intracellular free calcium (Ca-i(2+)) may play an essential role in the ischemia/reperfusion injury of skeletal muscle. Although it ha s been shown that Ca-i(2+) levels significantly increase during ischemia/re perfusion, it is still a matter of debate whether Ca-i(2+) increases during ischemia alone. It was the aim of this study to monitor the in vivo Ca-i(2 +) levels in the rat spinotrapezius muscle during ischemia of varying durat ion and reperfusion, using a ratiometric fluorescence technique, and to inv estigate the relationship between the postischemic flow patterns and Ca-i(2 +), if any. The muscle was loaded with Indo-1/AM and imaged by a cooled dig ital camera. Pre- and postischemic tissue perfusion was assessed by means o f an analogue camera. Our results show that short-term ischemia (5, 15 and 30 min) and subsequent reperfusion (60 min) does not alter Ca-i(2+) homeost asis and that tissue perfusion promptly recovers after the insult. One or t wo hours of ischemia resulted in changes in Ca-i(2+) levels, varying from p reparation to preparation; increases in some and no changes in others. In t hese preparations three distinct flow patterns - normal, compromised and no -reflow - could be distinguished during the 60-min reperfusion. Our main co nclusion is that in skeletal muscle Ca-i(2+) levels may increase, the incre ase probably depending on the muscle fiber type exposed.