Arachidonic Acid and GPR39 Modulate Coronary Autoregulation

The molecular basis of in vivo myogenic response and coronary autoregulation is unknown. We hypothesized that arachidonic acid (AA) participates in autoregulation through its metabolite, 15-hydroxyeicosatetraenoic acid (15-HETE), which activates GPR39 present in coronary arteriolar vascular smooth muscle cells (VSMCs). 15-HETE is the endogenous agonist for GPR39 and causes VSMC contraction by increasing cytosolic Ca ⁺⁺ through Gαq activation. Accordingly, isolated hearts from 103 wild type (WT) and 8 GPR39 knock out (KO) mice were perfused in a Langendorff system where coronary driving pressure (CDP) could be altered over a wide range (< 40–150 mmHg). WT hearts were perfused with modified Krebs-Henseleit buffer (mKHB) solution (n = 9), 10% plasma+mKHB (n = 7), and 3% fatty acid free albumin (FAFA)+mKHB (n = 8) over a wide range of CDPs. Autoregulation was only seen with plasma+mKHB. Since AA is the most abundant albumin-bound fatty acid in plasma, we infused different doses of AA with FAFA+mKHB (n = 36) at various CDPs in WT mouse hearts. Autoregulation was noted when 16 nmol AA was infused over 5 min and not at lower doses. The combination of mKHB+FAFA + AA produced autoregulation in all 10 WT hearts but not in any of the 8 GPR39 KO hearts. Because AA is released from plasma membrane by phospholipase A ₂ (PLA ₂ ), adding a specific PLA ₂ inhibitor (palmitoyl trifluoromethyl ketone, 10µM and 50µM) abolished autoregulation (n = 12) compared to vehicle (n = 7). A nonspecific Ca ⁺⁺ blocker, as well as inositol 1,4,5-trisphosphate, and transient receptor potential channel inhibitor (2-aminoethoxydiphenyl borate) almost abolished autoregulation in the doses used (n = 15) compared to vehicle (n = 7). We conclude that AA and GPR39 participate in the in vivo myogenic response that forms the basis of coronary autoregulation. In addition, PLA ₂ and mechanotransduction of coronary intraluminal pressure complete the feedback loop required for autoregulation.