Abstract
G A A b st ra ct s tension recordings of KCland bethanechol-induced contractions in circular orientated myenteric strips. Intracellular calcium was determined by fluorescencemicroscopy in isolated smooth muscle cells loaded with fura-2-AM (ExWL 340/380nm, EmWL 510nm) and calcium changes were expressed as the ratio between elicited fluorescence at 340nm and 380nm (F340/380). Mitochondrial membrane potential was measured in isolated colonic smooth muscle cells using the cell-permeant green fluorescent dye rhodamine 123 Results: Aging caused an increase in caffeine-induced Ca2+ release (140 % respect to adult cells) and a decrease in mitochondrial membrane potential, as indicated by the reduction of the heterogeneity of the rhodamine123 fluorescence signal in isolated cells. When mitochondria function was impaired using rotenone (1 μM) plus oligomycin (5 μM) the amplitude of Ca2+ release was significantly reduced (by 45%) and the [Ca2+]i decay showed a slower rate in senescent cells. Melatonin treatment protected from the deleterious effects of these agents. These changes in Ca2+ homeostasis did not translate into alterations in contractility, since pretreatment of both proximal and distal circular myenteric strips with rotenone, oligomicin of both for 30 min did not modify significantly the contractile response to neither KCl (60 mM) nor bethanechol (100 μM). Conclusion: Mitochondria play a more important role in Ca2+ homeostasis in aged than adult cells, however these changes are not enough to modify contractility, which suggest that in colonic smooth muscle mitochondrial respiratory chain is not essencial for contraction and that more sources of ATP than ATP synthase coexist in these cells. Supported by BFU2007-60563 and JEX
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