Myostatin Deficient Mice Display Altered Calcium Signaling

Abstract

Myostatin, a member of the transforming growth factor β family was shown to be a potent negative regulator of skeletal muscle growth. It is strongly expressed in skeletal muscle and myostatin deficient mice have a great increase in muscle mass. Yet, the physical performance of these animals is not improved or even suppressed as compared to control mice. To understand the possible underlying mechanisms we investigated the calcium homeostasis of skeletal muscle fibers from mice with the compact myostatin mutation (MstnCmpt-dlAbc).Resting membrane potentials were essentially identical on control and MstnCmpt-dlAbc mice (−79.2±0.3 vs. −78.0±0.3 mV). Action potentials (AP), evoked by field stimulation through a pair of platinum electrodes on single intact flexor digitorum brevis (FDB) muscle fibers, on the other hand, were significantly shorter on MstnCmpt-dlAbc animals. The average time between the peak and 90% repolarization of the AP corresponded to 0.92±0.03 vs. 0.78±0.02 ms on control and on MstnCmpt-dlAbc fibers, respectively. The other parameters of the APs were essentially identical.The resting and the depolarization-evoked changes in intracellular Ca2+ concentration ([Ca2+]i) were measured on single FDB fibers with the fluorescent dye Fura-2. While resting [Ca2+]i was higher (57.6±1.4 vs. 65.4±2.8 nM), the amplitude of the KCl-evoked calcium transients was smaller (360±49 vs. 215±44 nM) in MstnCmpt-dlAbc mice. Similar experiments were conducted on Fluo-3 loaded fibers using a confocal microscope and repeated (at 100 Hz for 200 ms) field stimulation. AP-evoked calcium transients were again smaller (2.75±0.15 vs. 2.20±0.14) on MstnCmpt-dlAbc fibers. Elementary calcium release events were detected using Fluo-3 on permeabilized FDB fibers. No significant difference in the parameters of sparks was observed between control and MstnCmpt-dlAbc mice.These results indicate that an alteration in calcium signaling might underlie the reduced muscle performance in myostatin deficient mice.