Objectives: 

To investigate the possible involvement of the senescence signalling kinase mTOR and the Ca2+ regulatory protein FKBP in age-related changes of IP3 receptors (IP3R)- and ryanodine receptors (RyR)-mediated Ca2+ signals.

Materials: 

Ca2+ signals were studied by fluorescent microscopy in fura-2 loaded colonic myocytes isolated from young (age 3-6 months) or old (24-30 months) guinea pigs. Cells were stimulated with a double pulse protocol with an intermediate period of 10 min to allow acute application of inhibitors. To compare the effects of inhibitors the second pulse was normalized to the first one. Significance was assessed by t test.

Results: 

The Ca2+ response to activation of cholinergic receptors (an IP3R-mediated signal) was significantly smaller in aged than in young animals. To assess the role of mTOR and FKBP in these changes we applied rapamycin, which inhibits mTOR by binding to FKBP, or the FKBP-calcineurin inhibitor FK506. Both treatments inhibited the cholinergic Ca2+ signals in young cells. Ku0063794, a mTOR inhibitor non targeted to FKBP had a similar inhibitory effect on the signal. The effect of rapamycin was enhanced in aged cells. The RyR-based calcium mobilization was studied with caffeine. Although, contrary to cholinergic stimulation, aging did not alter the amplitude of the caffeine-induced Ca2+ release, the underlying mechanisms are modified in aged cells. This is indicated by the finding that aging suppressed the inhibitory effect of rapamycin and FK506 on the response to caffeine. In contrast, the inhibitor Ku0063794 reduced to the same extent the caffeine response both in aged and young cells, suggesting that aging seems to operate via FKBP protein.

Conclusions: 

Our data indicate that aging impairs cholinergic Ca2+ signals in colonic myocytes, possibly by impairment of the mTOR-FKBP mediated facilitation of Ca2+ release.

Supported by BFU2011-24365, RETICEF RD06/0013/1012, FEDER and Junta de Extremadura (GR10009).