Potassium currents in human myogenic cells from donors of different ages

Potassium currents in human myogenic cells from healthy and congenital myotonic dystrophy foetuses

The whole-cell patch clamp technique was used to record potassium currents in in vitro differentiating myoblasts isolated from healthy and myotonic dystrophy type 1 (DM1) foetuses carrying 2000 CTG repeats. The fusion of the DM1 myoblasts was reduced in comparison to that of the control cells. The dystrophic muscle cells expressed less voltage-activated K(+) (delayed rectifier and non-inactivating delayed rectifier) and inward rectifier channels than the age-matched control cells. However, the resting membrane potential was not significantly different between the control and the DM1 cells. After four days in a differentiation medium, the dystrophic cells expressed the fast-inactivating transient outward K(+) channels, which were not observed in healthy cells. We suggest that the low level of potassium currents measured in differentiated DM1 cells could be related to their impaired fusion.

Calcium current kinetics in young and aged human cultured myotubes

There is evidence that the complex process of sarcopenia in human aged skeletal muscle is linked to the modification of mechanisms controlling Ca(2+) homeostasis. To further clarify this issue, we assessed the changes in the kinetics of activation and inactivation of T- and L-type Ca(2+) currents in in vitro differentiated human myotubes, derived from satellite cells of healthy donors aged 2, 12, 76 and 86 years. The results showed an age-related decrease in the occurrence of T- and L-type currents. Moreover, significant age-dependent alterations were found in L-(but not T) type current density, and activation and inactivation kinetics, although an interesting alteration in the kinetics of T-current inactivation was observed. The T- and L-type Ca(2+) currents play a crucial role in regulating Ca(2+) entry during satellite cells differentiation and fusion into myotubes. Also, the L-type Ca(2+) channels underlie the skeletal muscle excitation-contraction coupling mechanism. Thus, our results support the hypothesis that the aging process could negatively affect the Ca(2+) homeostasis of these cells, by altering Ca(2+) entry through T- and L-type Ca(2+) channels, thereby putting a strain on the ability of human satellite cells to regenerate skeletal muscle in elderly people.

The role of L- and T-type Ca2+ currents during the in vitro aging of murine myogenic (i28) cells in culture

The age-related decline in skeletal muscle strength could, in part, result from alterations in the mechanism of excitation-contraction coupling, responsible for muscle contraction. In the present work, we used the in vitro aging of murine myogenic (i28) cells as a model, to investigate whether the inefficiency of aged satellite cells to generate functional skeletal muscle fibres could be partly due to defective voltage-dependent Ca2+ currents. The whole-cell patch clamp technique was employed to measure L- and T-type Ca2+ currents in myotubes derived from the differentiation and fusion of these cells reaching replicative senescence. Our data showed that the expression and the amplitude of these currents decreased significantly during in vitro aging. Moreover, the analysis of the L-type current evoked in young and old cells by positive voltage steps, revealed no differences in the kinetics of activation, but significant alterations in the rate of inactivation. These effects of in vitro aging on voltage-dependent Ca2+ currents could also be related to their inability to fuse into myotubes. Taken together, our data support the hypothesis that age-related effects on voltage-dependent L- and T-type currents could be one of the causes of the failure of satellite cells to efficiently counteract the impairment in muscle force.