Arachidonic acid mediates non‐capacitative calcium entry evoked by CB 1 ‐cannabinoid receptor activation in DDT 1 MF‐2 smooth muscle cells

Cannabinoid CB 1 ‐receptor stimulation in DDT 1 MF‐2 smooth muscle cells induces a rise in [Ca 2+ ] i , which is dependent on extracellular Ca 2+ and modulated by thapsigargin‐sensitive stores, suggesting capacitative Ca 2+ entry (CCE), and by MAP kinase. Non‐capacitative Ca 2+ entry (NCCE) stimulated by arachidonic acid (AA) partly mediates histamine H 1 ‐receptor‐evoked increases in [Ca 2+ ] i in DDT 1 MF‐2 cells. In the current study, both Ca 2+ entry mechanisms and a possible link between MAP kinase activation and increasing [Ca 2+ ] i were investigated. In the whole‐cell patch clamp configuration, the CB‐receptor agonist CP 55, 940 evoked a transient, Ca 2+ ‐dependent K + current, which was not blocked by the inhibitors of CCE, 2‐APB, and SKF 96365. AA, but not its metabolites, evoked a transient outward current and inhibited the response to CP 55,940 in a concentration‐dependent manner. CP 55,940 induced a concentration‐dependent release of AA, which was inhibited by the CB 1 antagonist SR 141716. The non‐selective Ca 2+ channel blockers La 3+ and Gd 3+ inhibited the CP 55,940‐induced current at concentrations that had no effect on thapsigargin‐evoked CCE. La 3+ also inhibited the AA‐induced current. CP 55,940‐induced AA release was abolished by Gd 3+ and by phospholipase A 2 inhibition using quinacrine; this compound also inhibited the outward current. The CP 55,940‐induced AA release was strongly reduced by the MAP kinase inhibitor PD 98059. The data suggest that in DDT 1 MF‐2 cells, AA is an integral component of the CB 1 receptor signaling pathway, upstream of NCCE and, via PLA 2 , downstream of MAP kinase. © 2005 Wiley‐Liss, Inc.