Capillary endothelial Gq protein‐coupled receptors and PIP2 toggle signaling between TRPV4 and Kir2 channels in the brain

Abstract

The ion channel composition of capillaries is not known. Using freshly dissociated capillary endothelial cells (cECs) from mouse brain, we measured currents through strong inward rectifier K+ (Kir2.1) channels and through transient receptor potential vanilloid (TRPV4) channels. We have proposed that Kir2.1 and TRPV4 channels are involved in electrical and calcium signaling, respectively, to transmit signals from cECs to upstream arterioles. We tested the hypothesis that these two channel types are functionally linked through phosphatidylinositol 4,5‐bisphosphate (PIP2). We found that intracellular PIP2 or ATP had opposite effects on TRPV4 and Kir2.1 currents, with PIP2 or ATP suppressing TRPV4 channel activity and conversely being essential for Kir2.1 activity. The level of PIP2 is controlled by the activity of Gq protein‐coupled receptors (GqPCRs), which hydrolyze PIP2 to produce inositol 1,4,5‐triphosphate (IP3) and diacyglycerol (DAG). We therefore tested the effects of prostaglandin E2 (PGE2; an agonist of the GqPCR EP1), which has been implicated in neurovascular coupling, on TRPV4 and Kir2.1 currents in cECs, with the expectation of divergent effects on the two conductances. Indeed, when measured simultaneously in the same cECs, PGE2 increased TRPV4 currents with half‐time (t0.5) of 3.5 minutes and decreased Kir2.1 currents with a t0.5 of 5.3 minutes. In conclusion, the present study supports the concept that PIP2 tonically inhibits TRPV4 channels and activates Kir2.1 channels in the brain capillary endothelium. GqPCR activation therefore acts as a molecular switch that alters the balance between electrical (Kir2.1) and Ca2+ (TRPV4) signaling, which might change the signaling modality to upstream penetrating arterioles, and would have profound effects on the control of blood flow into the brain.Support or Funding InformationSupported by the NIH, Fondation Leducq and EC Horizon 2020 grants.