Melatonin Treatment Reverts Age-Related Changes in Guinea Pig Gallbladder Neuromuscular Transmission and Contractility

Abstract

The incidence of gallbladder illness increases with age, but the altered mechanisms leading to gallbladder dysfunction are poorly understood. Here we determine the age-related alterations in gallbladder contractility and the impact of melatonin treatment. Isometric tension changes in response to electrical field stimulation and to agonists were recorded from guinea pig gallbladder muscle strips. [Ca 2ϩ ] i was determined by epifluorescence microscopy in fura-2 loaded isolated gallbladder smooth muscle cells, and F-actin content was quantified by confocal microscopy. Aging reduced neurogenic contractions, which was associated with the impairment of nitrergic innervation and with increased responsiveness of capsaicin-sensitive relaxant nerves, possibly involving calcitonin gene-related peptide. Melatonin treatment for 4 weeks restored neurogenic responses to normal values, with an associated recovery of nitrergic function and the disappearance of the capsaicinsensitive component. Aging also reduced the contractile responses to cholecystokinin and Ca 2ϩ influx. The impaired contractility only correlated with diminished Ca 2ϩ mobilization in response to activation of Ca 2ϩ influx. Melatonin improved contractility and increased smooth muscle F-actin content without changing Ca 2ϩ homeostasis. In conclusion, aging impairs gallbladder function as the result of changes in the inhibitory neuromodulation of smooth muscle contractility and the reduction in the myogenic response to contractile agonists. Impaired contractility seems to be related to decreased Ca 2ϩ influx and damage of contractile proteins. Melatonin significantly ameliorated these age-related changes.

Aging impairs Ca2+ sensitization pathways in gallbladder smooth muscle

“…n=6-8 experiments. (*P<0.05, ** P<0.01, adult vs. aged) previously described (Gomez-Pinilla et al 2006), and here we confirm previous result showing that "in vivo" melatonin treatment for 28 days almost normalizes BE and CCK concentration-response curves (Fig. 7, left bars).…”

“…In the guinea pig gallbladder, aging reduced calcium influx but not calcium mobilization from internal stores even if contractile impairment is present for both maneuvers (Gomez-Pinilla et al 2006). These are clear evidences that changes in Ca 2+ homeostasis can neither fully explain the impairment in gallbladder contractility during aging nor the normalization in contractility induced by melatonin treatment even without the reestablishment of calcium influx (Gomez-Pinilla et al 2006). In this report, we show that impaired calcium sensitization pathways run in parallel with gallbladder hypomotility and decreased MLC20 phosphorylation.…”

“…In a previous report (Gomez-Pinilla et al 2006) we showed that aging impaired contraction of the guinea pig gallbladder in response to agonists. In the current study, we give some insights on the age induced alterations of stimulus-contraction coupling mechanisms.…”

“…It is well established that aging evokes tissuespecific changes in Ca 2+ homeostasis in nerves and in skeletal, cardiac and smooth muscles (Gomez-Pinilla et al 2007;Gomez-Pinilla et al 2011;PuzianowskaKuznicka and Kuznicki 2009). In the guinea pig gallbladder, aging reduced calcium influx but not calcium mobilization from internal stores even if contractile impairment is present for both maneuvers (Gomez-Pinilla et al 2006). These are clear evidences that changes in Ca 2+ homeostasis can neither fully explain the impairment in gallbladder contractility during aging nor the normalization in contractility induced by melatonin treatment even without the reestablishment of calcium influx (Gomez-Pinilla et al 2006).…”

“…We found that aging modifies neurological control of guinea pig gallbladder and impairs contractile response as the result of alterations in the contractile machinery without affecting calcium release from intracellular stores (Gomez-Pinilla et al 2006). The fact that impairment in the contractile capacity does not run in parallel with alterations in calcium signals suggests that calcium-independent mechanisms, such as calcium sensitization pathways, would be additional targets for the harmful effects of age.…”