Intracellular free [Ca2+] in human skeletal muscle with myopathic carnitine deficiency

Carnitine is required for the transport of activated long chain fatty acids through the mitochondrial inner membrane. We measured the intracellular free calcium concentration [( Ca2+]i) by means of a calcium selective microelectrode in skeletal muscle biopsies obtained from nine patients in which myopathic carnitine deficiency (MCD) was diagnosed, and from six subjects with no evidence of neuromuscular disease. Intact intercostal muscle bundles were dissected and then split for electron microscopic studies and electrophysiological measurements. The [Ca2+]i in muscle fibers from MCD patients was 0.46 +/- 0.02 mumol.l-1 (mean +/- SEM) and 0.10 +/- 0.01 mumol.l-1 in control subjects. At the electron microscopic level, the predominant abnormality was the presence of lipid vacuoles between the myofibrils. These results show that in patients with myopathic carnitine deficiency there is a significant increase in the resting myoplasmic calcium concentration which might be related to a malfunction of some mechanisms responsible for the homeostasis of intracellular calcium.