31–33 Interestingly, ICCs in the lamina propria respond to ATP but not to muscarinic agonist carbachol, MAPK Inhibitor Library while ICCs in the detrusor respond to carbachol via M3 receptor, indicating a parasympathetic control of ICCs in the detrusor.34 This implies the two types of ICCs have different functional
roles in the bladder physiology. Spontaneous electrical activity and Ca2+-transients in the ICCs and close structural connections with nerves and SMCs26,35 have suggested that the ICCs may be pacemaking cells of SCs in the bladder. Indeed, the c-Kit tyrosine kinase inhibitor imatinib mesylate inhibited SCs.36,37 However, the frequency of spontaneous Ca2+-transients differed between the ICCs and neighboring SMCs.38 This evidence contradicts the notion that ICCs in the bladder function as pacemakers. ICCs in the detrusor are positive for cyclooxygenase Selleckchem CP 673451 related to prostaglandins synthesis,39,40 and a recent study showed that ICCs in the detrusor have numerous vesicles, indicating a secretory function.41 Therefore, ICCs
may control the SMC activity by releasing a modulator. This is an attractive hypothesis. There are at least three factors that may contribute to changes in the SCs due to SCI or BOO: myogenic alterations, local mediators in the detrusor and urotheliogenic modulation (Table 1). SMCs have spontaneous electrical and contractile activity. However, electrical coupling is normally limited to some neighboring cells, and action potentials may spread through gap junctional intercellular communication.42 In BOO, cell-to-cell communication between primary cultured SMCs of bladders stained with a fluorescent dye was enhanced in SMCs from rats with BOO compared with those from control rats.43 This enhancement was inhibited by a gap-junction inhibitor. Enhanced cell-to-cell communication may, therefore, contribute to the enhanced SCs associated with BOO. The expression of
connexin 43 gap junctions between SMCs is increased in the human bladder with DO mainly due to SCI.44 This implies that intercellular communication between SMCs is enhanced and may result in enhanced SCs in SCI. Alterations in ion channel activity may be involved in the generation of enhanced SCs Etomidate in BOO. Downregulation of large and small conductance calcium-activated potassium channels and the TREK-1 potassium channel, and upregulation of calcium-activated chloride channels may cause enhanced SCs.45–47 However, there have been contradictory findings, namely, upregulated expression of potassium channels has also been identified in bladders with BOO.22 The reason for this contradiction is unknown. Further studies of alterations to potassium channels are required. There is an intracellular signal transduction mechanism that can increase the contractile ability of SMCs, that is, calcium sensitization that involves the rhoA/rho-kinase pathway.48 The expression of rhoA and rho-kinase was upregulated in obstructed rat bladders.