Characterization of sarcolemma and sarcoplasmic reticulum isolated from skeletal muscle of the freeze tolerant wood frog, Rana sylvatica: the β₂‐adrenergic receptor and calcium transport systems in control, frozen and thawed states

Abstract

In freeze tolerant wood frog Rana sylvatica, the freeze-induced liberation of glucose plays a critical role in survival in response to sub-zero temperature exposure. We have shown that the glycaemic response is linked to selective changes in the expression of hepatic adrenergic receptors through which catecholamines act to produce their hepatic glycogenolytic effects. The purpose of the present study was to determine if skeletal muscle, another catecholamine-sensitive tissue with glycogenolytic potential, displayed similar or different changes. In order to achieve these objectives, skeletal muscle derived from Rana sylvatica was studied in control, frozen and thawed states. In isolated sarcolemmal fractions, freezing effected an 88% decrease in beta(2)-adrenergic receptor expression but was without effect on the calcium pump; while thawing resulted in a recovery of the beta(2)-adrenergic receptor to 60% of control levels and a 2.4-fold increase in calcium transport. In isolated sarcoplasmic reticular fractions, freezing effected a 52% decrease in calcium binding and a 92% decrease in oxalate-stimulated calcium uptake; while thawing elicited partial normalization to control levels to 70% with respect to calcium binding and to 47% with respect to calcium uptake. Freezing and thawing were associated with increases and decreases, receptively, in blood glucose levels but were without effect on skeletal muscle glycogen content. Thus these muscle changes in Rana sylvatica in freezing and thawing are not linked to glycogen breakdown, are different from those previously seen in liver, and may provide a role in recovery of muscle function during thawing by protecting glycogen stores for contraction and maximizing extracellular calcium for excitation-contraction coupling in the frozen state. The involvement of thyroid hormone in triggering these muscle changes is discussed.

Protein kinase C in the wood frog,Rana sylvatica: reassessing the tissue-specific regulation of PKC isozymes during freezing

“…By contrast, past studies would suggest a need for PKC to remain active in muscle; these have shown that in response to freezing, IP 3 levels rose moderately, by 55%, in skeletal muscle (Holden & Storey, 1996; Holden & Storey, 1997). Moreover, calcium binding and uptake into the sarcoplasmic reticulum were strongly decreased in skeletal muscle of frozen frogs, leading to increased cytosolic calcium levels (Hemmings & Storey, 2001). However, in yet other studies, muscle IP 3 levels remained constant in frogs subjected to short-term anoxia at 5 °C, and then fell by 40% after 2 days of anoxic exposure.…”

Glycogen synthase kinase-3: cryoprotection and glycogen metabolism in the freeze-tolerant wood frog

“…Previous studies have shown that glycogenoloysis is stimulated by peripheral freezing through hormone-based mechanisms, such as -adrenergic signalling (Hemmings and Storey, 1994;Hemmings and Storey, 2001;Storey and Storey, 2004). It is possible that GSK-3 activation is mediated by similar hormonal action.…”

Regulation of sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) in turtle muscle and liver during acute exposure to anoxia

“…SERCA regulation in anoxic turtles of overall ATP hydrolyzed (Hochachka et al, 1996). Indeed, it has been shown that Na + /K + -ATPase and SERCA are closely regulated and are strongly suppressed in hypometabolic states including hibernation, estivation and diapause (MacDonald and Storey, 1999;Hemmings and Storey, 2001;Malysheva et al, 2001;Ramnanan and Storey, 2006;Ramnanan and Storey, 2008;McMullen and Storey, 2008). Anoxia has been shown to suppress SERCA activity in neurons (Henrich and Buckler, 2008) and hypoxia decreased SERCA expression in hearts (Pei et al, 2003) of rats.…”