Activation by Adenosine of Cultured Mesangial Cells: Receptors Involved and Intracellular Mechanisms

Abstract

We studied the effects of the adenosine (ADO) analogues R-PIA (Al agonist) and NECA (A2 agonist) on cAMP production and calcium inflow in cultured rat mesangial cells (MC). NECA, 10−6 M overstimulated cAMP content, and this effect was inhibited by the selective Al antagonist PD115199 (AT2, 10−6 M). R-PIA 10−6 M, decreased cAMP content in forskolin-stimulated MC and this effect was blocked by the selective A2 antagonist PD116948 (AT2, 10−6 M). In addition, 10−6 M R-PIA + 10−6 M AT2 increased 45Ca-uptake after 30 s of stimulation, whereas 10−6 M NECA + 10−6 M AT, mediated a reduction in 45Ca uptake in MC. Adenosine 10−4 M induced an increase in cAMP levels in forskolin-stimulated MC and an increase in 45Ca2+ uptake. Neither AT2 nor AT1 affected ADO-induced cAMP production in forskolin-stimulated MC, but this effect was inhibited by 10−4 M theophylline. ADO-induced 45Ca2+ uptake stimulation was inhibited by AT2, unlike the effect shown with R-PIA. This effect was also inhibited by AT1. These data demonstrate in a functional way the existence of A1 and A2 type receptors in cultured rat mesangial cells. Activation of the A1-type stimulates calcium entry and inhibits cAMP generation. In contrast, activation of the A2-type stimulates cAMP generation and inhibits calcium entry. Adenosine stimulates both cAMP generation and calcium uptake, but these actions do not seem to be mediated by the A1 or A2 receptors present in mesangial cells.