The phospholipid l‐α‐lysophosphatidylinositol ( LPI ), an endogenous ligand for GPR 55, is elevated in patients with acute coronary syndrome, and a GPR 55 antagonist cannabidiol ( CBD ) reduces experimental ischemia/reperfusion (I/R) injury. While LPI activates multiple signaling pathways, little is known about which ones are important in cardiomyocytes. In this study we explored whether activation of the Rho kinase/ ROCK /p38 MAPK pathway is responsible for LPI ‐induced extension of I/R injury. Using a high‐throughput screening method (dynamic mass redistribution; DMR ), mouse‐ and human‐induced pluripotent stem cell ( iPSC ) cardiomyocytes exposed to LPI were shown to exhibit a rapid, sustained, and concentration‐dependent (1 nmol L −1 ‐30 μmol L −1 ) cellular response. Y‐27632 ( ROCK inhibitor; 10 & 50 μmol L −1 ) and CBD (1 μmol L −1 ) both abolished the DMR response to LPI (10 μmol L −1 ). In murine iPSC cardiomyocytes, LPI ‐induced ROCK and p38 MAPK phosphorylation, both of which were prevented by Y‐27632 and CBD , but did not induce JNK activation or cleavage of caspase‐3. In hearts isolated from wild type ( WT ) mice subjected to 30 minutes global I/R, LPI (10 μmol L −1 ) administered via the coronary circulation increased infarct size when applied prior to ischemia onset, but not when given at the time of reperfusion. The exacerbation of tissue injury by LPI was not seen in hearts from GPR 55 −/− mice or in the presence of Y‐27632, confirming that injury is mediated via the GPR 55/ ROCK /p38 MAPK pathway. These findings suggest that raised levels of LPI in the vicinity of a developing infarct may worsen the outcome of AMI.

Mammalian voltage-activated L-type Ca 2+ channels, such as Ca(v)1.2, control transmembrane Ca 2+ fluxes in numerous excitable tissues. Here, we report that the pore-forming α1C subunit of Ca(v)1.2 is reversibly palmitoylated in rat, rabbit, and human ventricular myocytes. We map the palmitoylation sites to two regions of the channel: The N terminus and the linker between domains I and II. Whole-cell voltage clamping revealed a rightward shift of the Ca(v)1.2 current–voltage relationship when α1C was not palmitoylated. To examine function, we expressed dihydropyridine-resistant α1C in human induced pluripotent stem cell-derived cardiomyocytes and measured Ca 2+ transients in the presence of nifedipine to block the endogenous channels. The transients generated by unpalmitoylatable channels displayed a similar activation time course but significantly reduced amplitude compared to those generated by wild-type channels. We thus conclude that palmitoylation controls the voltage sensitivity of Ca(v)1.2. Given that the identified Ca(v)1.2 palmitoylation sites are also conserved in most Ca(v)1 isoforms, we propose that palmitoylation of the pore-forming α1C subunit provides a means to regulate the voltage sensitivity of voltage-activated Ca 2+ channels in excitable cells.

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