Aim: 

To check whether ageing reduces the contribution of Ca²⁺ sensitization to smooth muscle contraction and the effects of melatonin on this mechanism.

Methods: 

Isometric tension changes in response to agonists in the absence and presence of inhibitors of ROCK and PKC pathways were recorded from gallbladder muscle strips from adult (4 months old) and senescent (20 months old) guinea pigs. A group of senescent animals were treated with 2.5 mg/Kg/day of melatonin for 28 days. Levels of expression and phosphorylation of proteins involved in these pathways were determined by western blot.

Results: 

Maximal contractions in response to CCK were significantly reduced by aging and restored by melatonin treatment. Y27632 and GFX, inhibitors of ROCK and PKC pathways, respectively, had less inhibitory effects on CCK-induced contraction in senescent strips and recovered the inhibitory power in melatonin treated strips. These results suggest a reduction in the contribution of Ca²⁺ sensitization pathways in aged gallbladder smooth muscle, which we confirmed by the finding of decreased expression of ROCK I and II, PKC and MYPT-1. Most importantly, aging reduced CCK-induced phosphorylation of CPI-17 and MYPT-1, the two effectors of Ca²⁺ sensitization pathways, which would explain the lower contribution of Ca²⁺ sensitization in aged gallbladder contractility. Melatonin restored both the expression and phosphorylation of the components of ROCK and PKC pathways.

Conclusion: 

Ca²⁺ sensitization mechanisms are down regulated in aged guinea pig gallbladder and melatonin can be used to improve gallbladder function in aging.

Supported BFU 2007-60563 and RETICEF.