Cyclic ADP-ribose induces a larger than normal calcium release in malignant hyperthermia-susceptible skeletal muscle fibers

Abstract

Malignant hyperthermia (MH) is associated with abnormal regulation of intracellular calcium in skeletal muscle fibers. Cyclic adenosine diphosphate-ribose (cADPR) is an endogenous metabolite of β-NAD⁺ that induces Ca²⁺ release from intracellular stores in many tissues. Microinjection of cADPR (0.5 or 1 µM) increased the intracellular resting Ca²⁺ concentration ([Ca²⁺]_i) in intact swine skeletal muscle in a dose-dependent manner. However, the increase in [Ca²⁺]_i was greater in malignant-hyperthermia-susceptible (MHS) fibers than in non-susceptible (MHN) fibers. Incubation of muscle fibers in low external Ca²⁺ solution or in the presence of L-type Ca²⁺ channel entry blockers, or intracellular microinjection of heparin or ruthenium red did not modify the effect of cADPR on [Ca²⁺]_i. Dantrolene (50 µM), a known inhibitor of intracellular Ca²⁺ release, decreased resting [Ca²⁺]_i and prevented the cADPR-induced increase in [Ca²⁺]_i. These results provide evidence: (1) for the existence of Ca²⁺ release mechanisms occurring via non-ryanodine or inositol 1,4,5-trisphosphate (InsP ₃) receptor mechanisms; (2) that MHS skeletal muscles exhibit a higher responsiveness to cADP-ribose-induced release of Ca²⁺ and (3) that the ability of dantrolene to block cADP-ribose-induced release of Ca²⁺ could be related to its pharmacologic effect on resting [Ca²⁺]_i.