Short-term regulation of excitation-contraction coupling by the _1a subunit in adult mouse skeletal muscle

¹ Department of Pharmacology.Cinvestav
² Cinvestav-IPN
³ Dept. Pharmacol. Southern Illinois University
⁴ Dept. Physiol. Loyola University Chicago
⁵ CINVESTAV-I.P.N.

^* To whom correspondence should be addressed. E-mail: jsanchez{at}cinvestav.mx.

Submitted on May 23, 2005
Revised on June 27, 2005
Accepted on 13 September 2005

	Abstract

The _1a subunit of the skeletal muscle voltage-gated Ca²⁺ channel plays a fundamental role in the incorporation of the channel to the tubular system membranes as well as in channel function. In order to determine whether this auxiliary subunit is also a regulatory protein of Ca²⁺ release from the sarcoplasmic reticulum in vivo, we pressure-injected the _1a subunit into intact adult mouse muscle fibers and recorded, with Fluo3-AM, the Ca²⁺ signals generated by action potentials. We found that the _1a subunit significantly increased, within minutes, the amplitude of Ca²⁺ signals without major changes in their time course. Deletion of the carboxy-terminus region of the protein suppressed the modulatory action of the _1a subunit on Ca²⁺ signals. The possibility that potentiation of Ca²⁺ release is due to a direct interaction between the _1a subunit and the ryanodine receptor was ruled out by bilayer experiments of RyR1 single channel currents and also by Ca²⁺ flux experiments. Our data suggest that the _1a subunit is capable of regulating E-C coupling in the short term and that the integrity of the carboxy-terminus region is essential for its modulatory effect.

Key Words: Ca2+ release, DHP receptors, beta subunit, calcium channel, excitation-contraction coupling, skeletal muscle