Membrane potential, resting calcium and calcium transients in isolated muscle fibres from normal and dystrophic mice.

Abstract

SUMMARY1. Single skeletal muscle fibres were enzymatically isolated from the flexor digitorum brevis muscles (FDB) of dystrophic mdx and control C57BL/10 mice aged 3-9 weeks. In this age range the majority (> 95%) of the mdx fibres were morphologically normal.2. There was no significant difference between the resting membrane potential (RMP) of mdx and control mice, -71P2+ 1-21 (n = 26) and -70-6+ 1-15 mV (n = 42), respectively.3. At RMP more negative than -60 mV the resting calcium (recorded with fura-2, free acid ionophoresed into cell) in the dystrophic mdx cells was not significantly different from the normal animals, 45-7 + 4-1 (n = 10) and 46-2 +39 nm (n = 9), respectively.4. The resting cytosolic calcium concentration was measured simultaneously with the RMP. At RMP between -60 to -17 mV there was an increase in the resting calcium concentration in both mdx and control ranging from 79-3 to 252 nm. This increase was most probably due to the activation of the slow calcium current.5. Fura-2 calcium transients were produced via single action potential stimulation using an intracellular microelectrode both to stimulate the cell and record potential changes. There was no significant difference between the rise time (Tn) or half-decay time (Ti) at 22°C of the calcium transient in response to a single action potential in mdx compared to normal animals, 5-9 + 0-34 (n = 8) and 5-4 + 0-36 ms (n = 7); 39-5 + 2-9 (n = 8) and 40 75 + 3 7 ms (n = 7), respectively.6. In conclusion it appears that over the age range 3-9 weeks the absence of dystrophin does not affect the RMP, resting calcium or calcium transient parameters of morphologically normal FDB mtdx fibres.

Angiotensin II modulates mouse skeletal muscle resting conductance to chloride and potassium ions and calcium homeostasis via the AT1 receptor and NADPH oxidase

“…Resting membrane potential (RMP) values were in line with those described by others, with slight differences due to the different experimental conditions (26,27,35). However, RMP was not modified by ANG II in either normal and chloride-free physiological solutions (Fig.…”

Na+ Dysregulation Coupled with Ca2+ Entry through NCX1 Promotes Muscular Dystrophy in Mice

“…Initial attempts to directly measure Ca 2ϩ levels in dystrophic myofibers or myotubes led to equivocal results, with some observations supporting a general increase in total cytosolic Ca 2ϩ or subsarcolemmal Ca 2ϩ (5-10) and others showing no difference (11)(12)(13). These divergent accounts may reflect technical difficulties associated with measuring Ca 2ϩ in isolated fibers or myotubes, not to mention the uncertain physiological significance of such measurements in various ex vivo preparations or culture conditions.…”

“…However, the hypothesis that Ca 2ϩ elevations directly induce myofiber necrosis and lead to MD is controversial (2). While some groups have indeed reported global or even subsarcolemmal increases in Ca 2ϩ in dystrophic myofibers (5-10), such measurements are often technically difficult, which may be the reason why other studies have not observed a significant increase (11)(12)(13). Recent studies in transgenic (TG) mice have supported the Ca 2ϩ hypothesis of disease.…”

Alteration in Calcium Handling at the Subcellular Level inmdx Myotubes

“…In fact, whereas different groups (2, 13, 15) reported that the resting levels of cytosolic [Ca 2ϩ ] are higher in mdx or DMD compared with control cells and that this increase is a determinant factor leading to protease activation and subsequent muscular degeneration, other investigators (3, 4) could not confirm this difference. Controversial data have also been reported for the peak levels of [Ca 2ϩ ] c upon stimulation, some groups finding larger rises in mdx (15), others similar to controls (16), and some even reporting reductions (17). We have re-addressed this issue by using a different methodological and conceptual approach.…”