Adenosine stimulates Ca2+ fluxes and increases cytosolic free Ca2+ in cultured rat mesangial cells

Abstract

Adenosine has been associated with cellular Ca2+ metabolism in some cell types. Since adenosine is able to contract glomerular mesangial cells in culture, and since Ca2+ is the main messenger mediating contractile responses, we studied the effect of adenosine on 45Ca2+ movements into and out of mesengial cells and on the cytosolic free Ca2+ concentration ([Ca2+](i). Adenosine at 0.1 mM increased 45Ca2+ uptake (basal, 9993 ± 216; + adenosine, 14823 ± 410 d.p.m./mg; P < 0.01) through verapamil sensitive Ca2+ channels. These channels seem to be of the A1-adenosine receptor subtype. Adenosine also stimulated 45Ca2+ efflux from 45Ca2+-loaded mesangial cells. This effect was accompanied by a net depletion of intracellular 45Ca2+ content under isotopic equilibrium conditions (basal, 24213 ± 978; + adenosine, 18622 ± 885 d.p.m./mg; P < 0.05). The increase in 45Ca2+ efflux was inhibited by a Ca2+-free medium or in the presence of 10 μM-verapmil. However, the intracellular Ca2+-release blocker TMB-8 (10 μM) only partially inhibited the adenosine-stimulated 45Ca2+ efflux. In addition, adenosine induced an elevation in [(C)a2+](i) in mesangial cells with an initial transient peak within 15 s (basal, 113 ± 7; adenosine, 345 ± 46 nM), and a secondary increase which was slower (3-4 min) and of lower magnitude than the initial peak (250 ± 21 nM). In summary, adenosine elevates [Ca2+](i) and stimulates both Ca2+ uptake from the extracellular pool and Ca2+ efflux from intracellular pools in mesangial cells. The Ca2+ release from internal stores is produced by a combination of a TMB-8-inhibitable and a non-TMB-8-inhibitable mechanism, and seems to be dependent on Ca2+ influx.