Thermal dependency of electrical excitability of gastrocnemius (skeletal) muscle in the desert-reptile, Uromastix hardwickii

Abstract

This study deals with effects of seasonal temperature variations on muscular electrical excitability in the reptile Uromastix hardwickii. Freshly captured adult animals of both sexes were used, and the gastrocnemius (skeletal) muscles were dissected out. The muscle samples were digested with digestive fluid (pepsin and HCl), stirred, and the cells were allowed to settle out. The supernatant was removed leaving a whitish fluid containing clear cells that were used for “patch-clamp” recording of membrane ionic currents and potentials. Resting membrane potentials (RMPs) and action potentials of the cell membranes were measured using the whole-cell current mode. Glass microelectrodes, with a tip diameter 2–3 μm and tip resistance 5–6 MΩ (when filled with intracellular solution), were used. The mean values for RMP action potential and its duration showed no significant changes with the season, but other components of action potential, including threshold potential, after-potential, and its duration, were found to increase significantly (p < 0.05) in summer as compared to winter. This is the first study of seasonal temperature dependency of these parameters in the gastrocnemius muscle of U. hardwickii. This study shows that seasonal changes in components of the action potential are associated with changes in environmental temperature. These changes may be responsible for altered activities and homeostasis in these animals, and possibly related to the underlying mechanisms responsible for hibernation.