Ca2+ extrusion in aged smooth muscle cells

We investigated the effects of aging in Ca2+ extrusion mechanisms in smooth muscle bladder cells from 4 and 20–24-month-old guinea pigs using fluorescence microscopy and fura-2. Cells were challenged with a pulse of KCl immediately before perfusion with a Ca2+ free solution containing no inhibitors (control, untreated cells) or inhibitors of plasma membrane Ca2+ pump (PMCA, 1 mM La3+), Na+/Ca2+ exchanger (NCX, 1 μM SEA0400) or the sarcoendoplasmic Ca2+ pump (SERCA, 1 μM thapsigargin). Treatment of young adult cells with the inhibitors allowed estimating a relative contribution of 55% for NCX, 27% for PMCA and 31% for SERCA. Combination of two inhibitors at the same time showed the presence of interaction between extrusion mechanisms. In aged cells the [Ca2+]i extrusion was impaired due to decrease of PMCA activity, as revealed by the loss of effect of La3+, and to inhibitory interactions between NCX and SERCA activities, indicated by acceleration of decay in response to their respective inhibitors. In conclusion, in smooth muscle cells aging decreases the overall Ca2+ extrusion activity and modifies the interactions between the activities of the main Ca2+ removing mechanisms.