Cav1.1 Controls ATP Release in Adult Muscle Fibers

In adult muscle fibers, Cav1.1 acts as voltage sensor for both excitation-contraction coupling and the activation of a signaling cascade that regulates gene expression. We have shown that ATP is released trough pannexin-1 channels after electrical stimulation at 20 Hz, having a key role in the induction of transcriptional changes related to fast-to-slow muscle fiber phenotype transition. Myotubes lacking the Cav1.1-α1 subunit displayed almost no ATP release after electrical stimulation. The same was observed in adult fibers treated with the Cav1.1 antagonist nifedipine (25µM), showing that Cav1.1 has a central role controlling ATP release.We examined the activation of this signaling cascade in muscle fibers where a knock-down of the α1s subunit of Cav1.1 was obtained by a U7-exon skipping strategy using adenovirus-associated viral vectors (AAV-U7delα1s).Four months after AAV-U7delα1s injection we observed a significant reduction of Cav1.1 protein as well as atrophy and fibrosis of the treated muscles. Indo-1 Ca2+ transients and Ca2+ current in voltage-clamped fibers isolated from FDB treated muscles showed that the peak Ca2+ transient elicited by short depolarizing pulses was reduced by 35% whereas the maximal conductance of the Ca2+ channels was reduced by 30%. We also found increased basal ATP release with spontaneous release events. AAV-U7delα1s treated fibers showed higher mRNA levels of the slow isoform of Troponin I and lower mRNA levels of the fast isoform of Troponin I compared with non-treated muscles. The transcriptional changes observed in these two genes after electrical stimulation were absent in AAV-U7delα1s treated fibers.These results suggest that Cav1.1 controls ATP release trough Pannexin-1 channels, activating it after low stimulation frequencies and blocking ATP release during resting. The loss of this control perturbs the normal transcriptional response to electrical activity of adult muscle fibers.ACT1111, FONDECYT 1110467, FONDAP 15010006