L-Type Ca2+ Channel Charge Movement and Intracellular Ca2+ in Skeletal Muscle Fibers from Aging Mice

AbstractIn this work we tested the hypothesis that skeletal muscle fibers from aging mice exhibit a significant decline in myoplasmic Ca2+ concentration resulting from a reduction in L-type Ca2+ channel (dihydropyridine receptor, DHPR) charge movement. Skeletal muscle fibers from the flexor digitorum brevis (FDB) muscle were obtained from 5–7-, 14–18-, or 21–24-month-old FVB mice and voltage-clamped in the whole-cell configuration of the patch-clamp technique according to described procedures (Wang, Z.-M., M. L. Messi, and O. Delbono. 1999. Biophys. J. 77:2709–2716). Total charge movement or the DHPR charge movement was measured simultaneously with intracellular Ca2+ concentration. The maximum charge movement (Qmax) recorded (mean±SEM, in nC μF−1) was 53±3.2 (n=47), 51±3.2 (n=35) (non-significant, ns), and 33±1.9 (n=32) (p<0.01), for the three age groups, respectively. Qmax corresponding to the DHPR was 43±3.3, 38±4.1 (ns), and 25±3.4 (p<0.01) for the three age groups, respectively. The peak intracellular [Ca2+] recorded at 40mV (in μM) was 15.7±0.12, 16.7±0.18 (ns), and 8.2±0.07 (p