Comparison of signalling mechanisms involved in rat mesenteric microvessel contraction by noradrenaline and sphingosylphosphorylcholine

1 We have compared the signalling mechanisms involved in the pertussis toxin-sensitive and -insensitive contraction of rat isolated mesenteric microvessels elicited by sphingosylphosphorylcholine (SPC) and noradrenaline (NA), respectively. 2 The phospholipase D inhibitor butan-1-ol (0.3%). the store-operated Ca2+ channel inhibitor SK&F 96.365 (10 muM) the tyrosine kinase inhibitor genistein (10 muM), and the src inhibitor PP2 (10 muM) as well as the negative controls (0.3% butan-2-ol and 10 muM diadzein and PP3) had only little effect against either agonist. 3 Inhibitors of phosphatidylinositol-3-kinase (wortmannin and LY 294.001 10 muM each) or of mitogen-activated protein kinase kinase (PD 98,059 and U 126 10 muM each) did not consistently attenuate NA- and SPC-induced contraction as compared to their vehicles or negative controls (LY 303,511 or U 124). 4 The phospholipase C inhibitor U 73,122 (10 muM) markedly inhibited the SPC- and NA-induced contraction (70% and 88% inhibition of the response to the highest NA and SPC concentration, respectively), whereas its negative control U 73,343 (10 muM) caused only less than 30% inhibition. 5 The rho-kinase inhibitors Y 27 632 (10 muM) and fasudil (30 muM) caused a right ward-shift of the NA concentration-response curve by 0.7-0.8 log units and reduced the response to 10 muM SPC by 88% and 83%, respectively. 6 These data suggest that SPC and NA, while acting on different receptors coupling to different G-protein classes, elicit contraction of rat mesenteric microvessels by similar signalling pathways including phospholipase C and rho-kinase.