Depolarization-induced Potentiation Of Cav1.1 Does Not Require The Distal C-terminus

Abstract

In adult skeletal muscle, the majority of the L-type Ca2+ channel CaV1.1 subunit is truncated post-translationally at residue 1664 (PNAS, 102:5274-79), raising the question of the functional role of the distal residues (1665-1873). It has been suggested (J Neurosci.17:1243-55; J Biol Chem. 277:4079-87) that (i) the distal C-terminus is non-covalently associated with the remainder of the channel, (ii) reduces channel open probability, and (iii) loses this inhibitory effect as a result of phosphorylation during strong depolarization. In regard to point (ii), previous analysis of L-type ionic conductance (G) and membrane gating charge movements (Q) demonstrated that channel open probability (i.e., G/Q ratio) was indistinguishable for full-length or truncated (at 1662) CaV1.1 expressed in dysgenic myotubes (Nature 360:169-171). Here we have investigated the effects of removing the distal C-terminus on depolarization-induced potentiation of CaV1.1. Specifically, tail currents were measured for repolarization to -30 mV following a 200 ms depolarization to either +40 or +90 mV. For both full-length and truncated CaV1.1, tail currents were both larger (∼2.5-fold) and more slowly decaying (∼2-fold) following the +90 mV depolarization. Thus, we find no evidence for a role of the CaV1.1 distal C-terminus in depolarization-induced potentiation.We are currently examining the role of the CaV1.2 distal C-terminus by co-expression of full-length or truncated (1669) CaV1.2 in tsA-201 cells together with β2a and α2δ1. In agreement with previous work (J Physiol. 576:87-102, and in contrast to CaV1.1, truncation of CaV1.2 resulted in ∼4-fold increase in the G/Q ratio. We are currently investigating the ability of the truncated CaV1.2 to undergo depolarization-induced potentiation. Supported by NIH (NS24444) and MDA grants to KGB.