Catecholamines modulate podocyte function.

The aim of this study was to investigate the influence of adrenoceptor agonists on the intracellular calcium activity ([Ca2+]i), membrane voltage (Vm), and ion conductances (Gm) in differentiated mouse podocytes. [Ca2+]i was measured by the Fura-2 fluorescence method in single podocytes. Noradrenaline and the alpha 1-adrenoceptor agonist phenylephrine induced a reversible and concentration-dependent biphasic increase of [Ca2+]i in podocytes (EC50 approximately 0.1 microM for peak and plateau), whereas the alpha 2-adrenoceptor agonist UK 14.304 did not influence [Ca2+]i. The [Ca2+]i response induced by noradrenaline was completely inhibited by the alpha 1-adrenoceptor antagonist prazosin (10 nM). In a solution with a high extracellular K+ (72.5 mM), [Ca2+]i was unchanged and the [Ca2+]i increase induced by noradrenaline was not inhibited by the L-type Ca2+ channel blocker nicardipine (1 microM). Vm and Gm were examined with the patch-clamp technique in the slow whole-cell configuration. Isoproterenol, phenylephrine, and noradrenaline depolarized podocytes and increased Gm. The order of potency for the adrenoceptor agonists was isoproterenol (EC50 approximately 1 nM) > noradrenaline (EC50 approximately 0.3 microM) > phenylephrine (EC50 approximately 0.5 microM). The beta 2-adrenoceptor antagonist ICI 118.551 (5 to 100 nM) inhibited the effect of isoproterenol on Vm. Stimulation of adenylate cyclase by forskolin mimicked the effect of isoproterenol on Vm and Gm (EC50 approximately 40 nM). Isoproterenol induced a time- and concentration-dependent increase of cAMP in podocytes. The effect of isoproterenol was unchanged in the absence of Na+ or in an extracellular solution with a reduced Ca2+ concentration, whereas it was significantly increased in an extracellular solution with a reduced Cl- concentration (from 145 to 32 mM). The data indicate that adrenoceptor agonists regulate podocyte function: They increase [Ca2+]i via an alpha 1-adrenoceptor and induce a depolarization via a beta 2-adrenoceptor. The depolarization is probably due to an opening of a cAMP-dependent Cl- conductance.