Sustained overexpression of IGF-1 prevents age-dependent decrease in charge movement and intracellular Ca2+ in mouse skeletal muscle

In this work we tested the hypothesis that transgenic sustained overexpression of IGF-1 prevents age-dependent decreases in charge movement and intracellular Ca2+ in skeletal muscle fibers. To this end, short flexor digitorum brevis (FDB) muscle fibers from 5-7- and 21-24-month-old FVB (wild-type) and S1S2 (IGF-1 transgenic) mice were studied. Fibers were 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). Charge movement and intracellular Ca2+ concentration were recorded simultaneously. The maximum charge movement (Q(max)) recorded in young wild-type and transgenic mice was (mean +/-SEM, in nC muF(-1)): 52 +/- 2.1 (n = 46) and 54 +/- 1.9 (n = 38) (non-significant, ns), respectively, whereas in old wild-type and old transgenic; mice the values were 36 +/- 2.1 (n = 32) and 49 +/- 2.3 (n = 35), respectively (p < 0.01). The peak intracellular calcium [Ca2+](i) recorded in young wild-type and transgenic mice was (in mu M): 14.5 +/- 0.9 and 16 +/- 2.1 (ns), whereas in old wild-type and transgenic mice the values were 9.9 +/- 0.1 and 14 +/- 1.1 (p < 0.01), respectively. No significant changes in the voltage distribution or steepness of the Q-V or [Ca2+]-V relationship were found. These data support the concept that overexpression of IGF-1 in skeletal muscle prevents age-dependent reduction in charge movement and peak [Ca2+](i).