β-Adrenergic control of sarcolemmal CaV1.2 abundance by small GTPase Rab proteins

Silvia G. del Villar, Taylor L. Voelker, Maartje Westhoff, Gopireddy R. Reddy, Heather C. Spooner, Manuel F Navedo, Eamonn J. Dickson, Rose E. Dixon

Research output: Contribution to journalArticlepeer-review

Abstract

The number and activity of Cav1.2 channels in the cardiomyocyte sarcolemma tunes the magnitude of Ca2+-induced Ca2+ release and myocardial contraction. β-Adrenergic receptor (βAR) activation stimulates sarcolemmal insertion of CaV1.2. This supplements the preexisting sarcolemmal CaV1.2 population, forming large “superclusters” wherein neighboring channels undergo enhanced cooperative-gating behavior, amplifying Ca2+ influx and myocardial contractility. Here, we determine this stimulated insertion is fueled by an internal reserve of early and recycling endosome-localized, presynthesized CaV1.2 channels. βAR-activation decreased CaV1.2/endosome colocalization in ventricular myocytes, as it triggered “emptying” of endosomal CaV1.2 cargo into the t-tubule sarcolemma. We examined the rapid dynamics of this stimulated insertion process with live-myocyte imaging of channel trafficking, and discovered that CaV1.2 are often inserted into the sarcolemma as preformed, multichannel clusters. Similarly, entire clusters were removed from the sarcolemma during endocytosis, while in other cases, a more incremental process suggested removal of individual channels. The amplitude of the stimulated insertion response was doubled by coexpression of constitutively active Rab4a, halved by coexpression of dominant-negative Rab11a, and abolished by coexpression of dominant-negative mutant Rab4a. In ventricular myocytes, βARstimulated recycling of CaV1.2 was diminished by both nocodazole and latrunculin-A, suggesting an essential role of the cytoskeleton in this process. Functionally, cytoskeletal disruptors prevented βARactivated Ca2+ current augmentation. Moreover, βAR-regulation of CaV1.2 was abolished when recycling was halted by coapplication of nocodazole and latrunculin-A. These findings reveal that βARstimulation triggers an on-demand boost in sarcolemmal CaV1.2 abundance via targeted Rab4a- and Rab11a-dependent insertion of channels that is essential for βAR-regulation of cardiac Ca 1 2.

Original languageEnglish (US)
Article numbere2017937118
JournalProceedings of the National Academy of Sciences of the United States of America
Volume118
Issue number7
DOIs
StatePublished - Feb 16 2021

Keywords

  • Cardiac EC-coupling
  • Ion channel clustering
  • L-type calcium channel
  • Trafficking
  • β-adrenergic receptor

ASJC Scopus subject areas

  • General

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