Urinary bladder disturbances are frequent in the elderly population but the responsible mechanisms are poorly understood. This study evaluates the effects of aging on detrusor myogenic contractile responses and the impact of melatonin treatment. The contractility of bladder strips from adult, aged and melatonin-treated guinea pigs was evaluated by isometric tension recordings. Cytoplasmatic calcium concentration was estimated by epifluorescence microscopy of fura-2-loaded isolated detrusor smooth muscle cells, and the levels of protein expression and phosphorylation were quantitated by western blotting. Ageing impairs the contractile response of detrusor strips to cholinergic and purinergic agonists and to membrane depolarization. The impaired contractility correlates with increased [Ca²⁺]_i in response to the stimuli, suggesting a reduced Ca²⁺ sensitivity. Indeed, the agonist-induced contractions in adult strips were sensitive to blockade with Y27362, an inhibitor of Rho kinase (ROCK) and GF109203X, an inhibitor of protein kinase C (PKC), but these inhibitors had negligible effects in aged strips. The reduced Ca²⁺ sensitivity in aged tissues correlated with lower levels of RhoA, ROCK, PKC and the two effectors CPI-17 and MYPT1, and with the absence of CPI-17 and MYPT1 phosphorylation in response to agonists. Interestingly, melatonin treatment recovered impaired contractility via normalization of Ca²⁺ handling and Ca²⁺ sensitizations pathways. Melatonin beneficial effects correlated with the restoration of oxidative stress parameters. These results suggest that melatonin might be a novel therapeutic tool to palliate ageing-related urinary bladder contractile impairment.

Supported by 2PR03A020, BFU2004-0637 to M.J.P, VR 71X-28 to P.H., VR 71X-14955 to K.S. and VR K2007-65X-20418-01-3 to M.F.G