Impaired excitation–contraction coupling in muscle fibres from the dynamin2^R465W mouse model of centronuclear myopathy

Abstract

Mutations in the gene encoding dynamin 2 (DNM2) are responsible for autosomal dominant centronuclear myopathy (AD-CNM). We studied the functional properties of Ca signalling and excitation-contraction (EC) coupling in muscle fibres isolated from a knock-in (KI) mouse model of the disease, using confocal imaging and the voltage clamp technique. The transverse-tubule network organization appeared to be unaltered in the diseased fibres, although its density was reduced by ∼10% compared to that in control fibres. The density of Ca current through CaV1.1 channels and the rate of voltage-activated sarcoplasmic reticulum Ca release were reduced by ∼60% and 30%, respectively, in KI vs. control fibres. In addition, Ca release in the KI fibres reached its peak value 10-50 ms later than in control ones. Activation of Ca transients along the longitudinal axis of the fibres was more heterogeneous in the KI than in the control fibres, with the difference being exacerbated at intermediate membrane voltages. KI fibres exhibited spontaneous Ca release events that were almost absent from control fibres. Overall, the results of the present study demonstrate that Ca signalling and EC coupling exhibit a number of dysfunctions likely contributing to muscle weakness in DNM2-related AD-CNM.

Skeletal muscle MACF1 maintains myonuclei and mitochondria localization through microtubules to control muscle functionalities

“…Figure 7H shows rhod-2 Ca 2+ transients elicited by membrane depolarizing steps of increasing amplitude in a Macf1 f/f Cre- and in a Macf1 f/f Cre+ fibers. As routinely observed under these conditions (Kutchukian et al, 2017), transients in control fibers exhibit a fast early rising phase upon depolarization followed by a slower phase at low and intermediate voltages and by slowly decaying phase for the largest depolarizing steps. As shown in figure 7I, rhod-2 transients from Macf1 f/f Cre+ fibers exhibit an overall similar time-course, not distinguishable from control muscle fibers.…”

Differential physiological roles for BIN1 isoforms in skeletal muscle development, function and regeneration

“…Intracellular equilibration of the solution was allowed for 30 min. For calcium current analysis, linear leak component was removed as previously described (Kutchukian et al 2017). The voltage dependence of the peak current was fitted with the following equation:…”

Differential physiological role of BIN1 isoforms in skeletal muscle development, function and regeneration

“…For both di-8-anepps and fluo-4 imaging, fluorescence was collected above 505 nm with 488 nm excitation. The T-tubule density from the di-8-anepps fluorescence was estimated as described previously (Kutchukian et al 2017).…”