Muscarinic modulation of Cav2.3 (R-type) calcium channels is antagonized by RGS3 and RGS3T Article uri icon

abstract

  • Ca2%2b influx through voltagegated R-type (CaV2.3) Ca2%2b channels is important for hormone and neurotransmitter secretion and other cellular events. Previous studies have shown that CaV2.3 is both inhibited and stimulated through signaling mechanisms coupled to muscarinic ACh receptors. We previously demonstrated that muscarinic stimulation of CaV2.3 is blocked by regulator of G protein signaling (RGS) 2. Here we investigated whether muscarinic inhibition of CaV2.3 is antagonized by RGS3. RGS3 is particularly interesting because it contains a lengthy (∼380 residue) amino-terminal domain of uncertain physiological function. CaV2.3, M2 muscarinic ACh receptors (M 2R), and various deletion mutants of RGS3, including its native isoform RGS3T, were expressed in HEK293 cells, and agonist-dependent inhibition of CaV2.3 was quantified using whole cell patch-clamp recordings. Full-length RGS3, RGS3T, and the core domain of RGS3 were equally effective in antagonizing inhibition of CaV2.3 through M2R. These results identify RGS3 and RGS3T as potential physiological regulators of R-type Ca2%2b channels. Furthermore, they suggest that the signaling activity of RGS3 is unaffected by its extended amino-terminal domain. Confocal microscopy was used to examine the intracellular locations of four RGS3-enhanced green fluorescent protein fusion proteins. The RGS3 core domain was uniformly distributed throughout both cytoplasm and nucleus. By contrast, full-length RGS3, RGS3T, and the amino-terminal domain of RGS3 were restricted to the cytoplasm. These observations suggest that the amino terminus of RGS3 may serve to confine it to the cytoplasmic compartment where it can interact with cell surface receptors, heterotrimeric G proteins, and other signaling proteins. Copyright © 2007 the American Physiological Society.

publication date

  • 2007-01-01