CONTRACTILITY AND PHENOTYPE TRANSITIONS IN SEROSAL THICKENING OF OBSTRUCTED RABBIT BLADDER

Partial outlet obstruction of rabbit bladder induces serosal thickenin g and smooth muscle (SM) cell hypertrophy that are accompanied by phen otypic changes in the expression of cytoskeletal and cytocontractile p roteins. In the present study, we compare the observed progressive phe notypic changes with the contractile responses of strips of the thicke ned serosa. At 15 days after partial outlet obstruction, although cell s in thickened serosa demonstrate the presence of nonmuscle (NM) myosi n of A-like type, vimentin, and SM alpha-actin, no contractile respons es of this tissue were noted. At later times (30 days), this tissue ex pressed in addition SM myosin, and this pattern was paralleled by the development of KCl-stimulated contractility. It is only after 60 days that the serosa demonstrated the ex:pression of desmin, phosphoglucomu tase (PGM)-related protein, and was locally negative for NM myosin, in dicating a maturation toward adult SM cells. Concomitant to this pheno typic change, the response to KCl increased, and a bethanechol-stimula ted contractile response developed. At no time period did the serosal layer react with anti-synaptophysin or anti-neurofilament proteins nor did the strips respond to field stimulation (via release of neurotran smitters), showing that SM cell differentiation and development of con tractile responses during serosal thickening are independent of innerv ation.