Effects of TRIM on tension, intracellular calcium and nitrergic transmission in the rat anococcygeus muscle

The effects of the putatively selective inhibitor of neuronal nitric oxide synthase (nNOS) 1-(2-trifluoromethylphenyl) imidazole (TRIM) were investigated on contractility, intracellular calcium and nitrergic relaxations in the rat anococcygeus muscle. TRIM (100-1000 mu M) reduced the tension of rat anococcygeus muscles when contracted with guanethidine (10 mu M) and clonidine (0.1 mu M). Relaxations to TRIM persisted in the presence of the non-selective NOS inhibitor L-NAME (100 mu M) and the inhibitor of soluble guanylate cyclase ODQ (1 mu M). TRIM also reduced tension when muscles were contracted with phenylephrine (3 mu M), noradrenaline (3 mu M) or high K physiological salt solution (high KPSS; 60 mM). Influx of calcium ([Ca2+](i)) in response to high KPSS was significantly reduced in the presence of TRIM (1 mM). TRIM also inhibited the influx of Ca-45(2+) induced by KPSS, but had no effect on the influx induced by phenylephrine (10 mu M). TRIM (300 mu M) had a modest, but significant, inhibitory effect on nitrergic relaxations that were evoked by electrical field stimulation (1-10 Hz, 15 V, 10 s trains) in muscles contracted with guanethidine and clonidine. In contrast, L-NAME (1-100 mu M) inhibited these nitrergic responses with an IC50 of 9.31 +/- 0.87 mu M (n=4). The results suggest that the smooth muscle relaxant effect of TRIM in the rat anococcygeus muscle may affect the entry of Ca2+ possibly through voltage-operated calcium channels. Furthermore, the relatively modest effect of TRIM on nitrergic responses indicates that it is not a particularly reliable inhibitor of nNOS.