Changes in smooth muscle cell phenotype and contractile function following ischemia-reperfusion injury in the rat urinary bladder.

Twenty-eight adult male Sprague-Dawley rats were divided into four groups: Group 1 received 1 hour (h) of bilateral ischemia alone. Groups 2 and 3 received 1 h ischemia followed by 1 and 4 h of reperfusion (I-R), respectively. Group 4 consisted of age-matched control rats. Bladder strips were studied using electrical field stimulation (EFS) and KCl stimulation. Maximal contractile responses were recorded and analyzed. Temporal patterns of changes in phenotypic (non-contractile and contractile) expression of bladder smooth muscle cells were investigated using electron microscopy. The mean ratio of non-contractile to contractile phenotype (nc/c) of smooth muscle cells (SMCs) in the control group was 0.169. In the ischemia alone group, the ratio was 0.991. In the 1 h I-R group, the ratio 0.865 whereas in 4 h I-R group the ratio 1.601. The contractile responses to EFS and KCl showed decreased responses in all groups. These results clearly demonstrated that the ratio of nc/c increased significantly in the ischemia group and further increased significantly in both I-R groups. The contractile responses decreased in all ischemic groups although the magnitude of the contractile changes did not correspond in the change of phenotype ratio.