Alterations in intracellular free Ca2+ handling in mouse models for Duchenne muscular dystrophy

Abstract

Duchenne muscular dystrophy (DMD) is a progressive degenerative muscle disease that affects 1 out of 3500 boys. It is known that the mouse model most frequently used in DMD research, the mdx mice, upregulates utrophin (utr), a protein with similar roles as dystrophin. Thus, the mdx/utr−/− double mutant (DM) is an alternative model that may be a more appropriate model for studying DMD disease mechanisms. One proposed mechanism behind the disease progression is related to poor intracellular calcium ([Ca2+]i) handling. The purpose of the current study was to evaluate the [Ca2+]i levels in response to repeated tetanic stimulation in intact single muscle fibres from the DM mouse model in comparison to fibres from mdx mice. Single muscle fibres were obtained from the flexor digitorum brevis by collagenase digestion and loaded with Fura‐2 AM for [Ca2+]i assessment at a range of stimulation frequencies (10, 30, 50, 70, 100, 120 and 150Hz). There were no differences for peak Fura‐2 ratio at any of the stimulation frequencies but the resting Fura‐2 ratio was reduced in the DM compared to the mdx mice (0.361±0.029 vs 0.381±0.019; p<0.05). The diameter and length of muscle fibres from DM were smaller compared to the mdx group (p<0.05). Furthermore, 65% of the fibres from DM animals failed to maintain peak Ca2+ during a tetanus, while 43% of the mdx fibres failed. These data suggest that alterations in the Ca2+ handling properties may be due to plasma or t‐tubule membrane conductance abnormalities and/or impaired Ca2+ release or storage by the sarcoplasmic reticulum. This project has been funded by Department of Kinesiology Graduate Research Initiative Project (GRIP).