Coincident intracellular calcium rise is essential for Gi/o‐mediated activation of TRPC4 (843.3)

TRPC4 is a member of the Canonical Transient Receptor Potential family of non‐selective cation channels. Na + and Ca 2+ influx through the active TRPC4 channel elicits membrane depolarization and intracellular Ca 2+ signaling in various cell types including neurons, vascular endothelium and smooth muscle cells. It has been well‐established that homomeric TRPC4 channels are synergistically activated by co‐stimulation of two separate G protein pathways, G q/11 and G i/o . However, it remains unclear which step(s) or constituent(s) of the G q/11 pathway is(are) essential for synergizing with G i/o proteins to maximally activate TRPC4 channels. Using patch‐clamp recordings and fluorescence membrane potential measurements in HEK293 cells heterologously coexpressing mouse TRPC4β and G i/o ‐coupled µ opioid receptor, we have identified intracellular Ca 2+ rise as the primary event associated with G q/11 activation that synergizes with G i/o stimulation to elicit maximal TRPC4 current. We also show that a signification portion of this effect is independent of calmodulin although Ca 2+ ‐calmodulin can enhance channel activation. Our experiments demonstrate the contribution of phosphoinositide hydrolysis and IP 3 receptors but rule them out as essential players. These findings argue for a critical role of intracellular Ca 2+ rise in TRPC4 activation by G i/o ‐coupled receptors and illustrate the key requirements that support TRPC4 as a coincidence sensor of multiple signaling pathways. Grant Funding Source : American Heart Association