Regional differences in signalling transduction pathways among smooth muscle cells from rabbit colon

Smooth muscle cells (SMC) from the circular muscle layer of rabbit colon, t aken from the proximal and distal regions that are known to have different physiological and motor activities, were used to highlight distinct regiona l intrinsic myogenic properties and to investigate the correlations between receptor and signalling transduction pathways. Contractile agonists were s hown to be more potent on proximal than on distal SMC in inducing contracti on and intracellular Ca2+ increase. Concentration-response curves of agonis ts-induced Ca2+ increase were constantly shifted to the right, though remai ning parallel, with respect to contraction curves, independently of the reg ion analysed. Using agents activating different steps of cAMP-or cGMP-media ted intracellular cascades, main regional differences were revealed as far as relaxation was concerned. Relaxation of proximal SMC was found to be ess entially cGMP mediated, while that of distal SMC was cAMP mediated. In conc lusion, the motor patterns of the two regions appear to be influenced by di stinct regional biochemical characteristics that are intrinsic to colonic S MC. (C) 2000 Elsevier Science Inc. All rights reserved.