Characterization of G proteins involved in activation of nonselective cation channels and arachidonic acid release by norepinephrine/ 1A-adrenergic receptors

Kawanabe, Yoshifumi, Nobuo Hashimoto, and Tomoh Masaki. Characterization of G proteins involved in activation of nonselective cation channels and arachidonic acid release by norepinephrine/ 1Aadrenergic receptors. Am J Physiol Cell Physiol 286: C596–C600, 2004; 10.1152/ajpcell.00359.2003.—We demonstrated recently that norepinephrine activates Ca -permeable nonselective cation channels (NSCCs) in Chinese hamster ovary cells stably expressing 1A-adrenergic receptors (CHO1A). Moreover, extracellular Ca through NSCCs plays essential roles in norepinephrine-induced arachidonic acid release. The purpose of the present study was to identify the G proteins involved in the activation of NSCCs and arachidonic acid release by norepinephrine. For these purposes, we used U73122, an inhibitor of phospholipase C (PLC), and dominant negative mutants of G12 and G13 (G12G228A and G13G225A, respectively). U73122 failed to inhibit NSCCs activation by norepinephrine. The magnitudes of norepinephrine-induced extracellular Ca influx in CHO1A microinjected with G13G225A were smaller than those in CHO1A. In contrast, the magnitudes of norepinephrine-induced extracellular Ca influx in CHO1A microinjected with G12G228A were similar to those in CHO1A. In addition, neither a Rhoassociated kinase (ROCK) inhibitor nor a phosphoinositide 3-kinase inhibitor affected norepinephrine-induced extracellular Ca influx. G13G225A, but not G12G228A, also inhibited arachidonic acid release partially. These results demonstrate that 1) the Gq/PLC-pathway is not involved in NSCCs activation by norepinephrine, 2) G13 couples with CHO1A and plays important roles for norepinephrine-induced NSCCs activation, 3) neither ROCKnor PI3K-dependent cascade is involved in NSCCs activation, and 4) G13 is involved in norepinephrine-induced arachidonic acid release in CHO1A.