21 DHPR is a critical element for excitation-coupled calcium entry (ECCE) but not formation of tetrads in skeletal myotubes

¹ Medical University of Lodz
² School of Veterinary Medicine, University of California, Davis
³ Colorado State University
⁴ Brigham and Women's Hospital
⁵ University of Colorado Health Sciences Center
⁶ College of Veterinary Medicine, University of California, Davis
⁷ College of Medicine, University of Pennsylvania

^* To whom correspondence should be addressed. E-mail: allen{at}zeus.bwh.harvard.edu.

Submitted on August 2, 2007
Revised on September 7, 2007
Accepted on 11 December 2007

	Abstract

Previously, it was shown that siRNA partial knock-down of the and[alpha]2and[delta]1 DHPR subunits caused a significant increase in the rate of activation of the L-type Ca²⁺ current in myotubes but had little or no effect on skeletal EC coupling (1). The current study used permanent siRNA knock-down of ₂₁ to address two important unaddressed questions. First, does the and ₂₁ subunit contribute to the size and/or spacing of tetradic particles? Second, is the and ₂₁ subunit important for ECCE (2, 3)? We found that the size and spacing of tetradic particles is unaffected by siRNA knock-down of and[alpha]2and[delta]1, indicating that the visible particle represents the ₂₁leads to a complete loss of ECCE during KCl depolarization, and a more rapid decay of Ca²⁺ transients during bouts of repetitive electrical stimulation like those occurring during normal muscle activation in vivo. Thus we conclude that the ₂₁ DHPR subunit is physiologically necessary for sustaining Ca²⁺ transients in response to prolonged depolarization or repeated trains of action potentials.

Key Words: : α2δ1 Dihydropyridine Receptor subunit, Dihydropyridine Receptor, EC coupling, Excitation Coupled Calcium Entry, Muscle, ryanodine receptor