Partial bladder outlet obstruction (PBOO) alters the function of the whole bladder and produces specific alterations in the contractility of the bladder smooth muscle cell. The goal of this study was to test the hypothesis that PBOO affects smooth muscle contraction at the level of the receptor and G-protein dependent increase in myofilament Ca²⁺ sensitivity. To address this question, we used -toxin permeabilized strips of bladder smooth muscle from control animals and animals subjected to two weeks of PBOO. Increasing free [Ca²⁺] increased force in permeabilized strips from control animals; the addition of 10 µM carbachol and 10 µM GTP increased both the Ca²⁺ sensitivity of the contractions and the maximal levels of force attained. In contrast, although increases in [Ca²⁺] increased force in permeabilized strips from PBOO animals, the addition of carbachol and GTP had no additional effects. MLC phosphorylation levels increased with [Ca²⁺] and although they tended to be higher in strips from PBOO animals, did not reach statistical significance. Assessment of G-protein activity from both animal models suggests this is not a site responsible for the loss of carbachol and GTP enhancement of myofilament Ca²⁺ sensitivity. The addition of phorbol dibutyrate increased the Ca²⁺ sensitivity of force development in strips from both animal models suggesting that an alteration in protein kinase C signaling is not involved. Our results are consistent with the hypothesis that PBOO decreases receptor mediated myofilament calcium sensitization and that the site of action is downstream from either the G-proteins or protein kinase C.