This study was carried out to analyze the developmental changes of bladder response to cholinergic stimulation in detail, highlighting calcium sensitization (CS) and its related pathways. Rats were divided into three groups in accordance with reported time of developmental milestones (newborn: day 1-4, youngster: day 5-14 and grown-up: day 15-21). Following cholinergic stimulation (carbachol 5 uM) the contractile response to detrusor were analyzed with respect to three phases (initial phasic, tonic and superimposed phasic contractions). Contractile responses were analyzed by dynamic and kinetic aspects. The responses were further compared in varying external calcium concentrations and in the presence of inhibitors of protein kinase C (PKC) and Rho kinase (ROCK), which are involved in CS. The responses of newborns were contrasted to the others by the short and brisk initial phasic contractions, prominent tonic contractions and delayed participation of irregular superimposed phasic contractions. With development, phasic contractions became prominent and tonic contractions diminished. These developmental changes of phasic contractions were reproduced when exposed to increasing calcium concentrations. Application of specific inhibitors and molecular phasic analysis revealed that PKC was functional in tonic contractions of the newborn, whereas ROCK took over its role with development. Within a few days of birth, rats' bladders experienced drastic changes of contractile mechanisms. These included dominance of phasic contractions from tonic contractions due to increased calcium dependence and the maturational shift of calcium sensitivity mechanism from PKC to ROCK.