Angiotensin II increases the cytosolic calcium activity in rat podocytes in culture. In the glomerulus, angiotensin II (Ang II) reduces the ultrafiltration coefficient and enhances the filtration of macromolecules. During glomerular injury, inhibition of the renin-angiotensin system by angiotensin-converting-enzyme inhibitors reduces proteinuria and retards the progression to end-stage renal insufficiency. The mechanisms by which Ang II modulates glomerular function are still a matter of investigation. To study whether Ang II may regulate the cytosolic calcium activity ([Ca²⁺]_i) in podocytes, these cells were propagated in short-term culture and the effect of Ang II was examined with the Fura-2 microfluorescence technique in single podocytes. The cellular identity of cultured podocytes was proven by the expression of WT-1 and pp44, specific antibodies against podocytes in vivo. Ang II led to a concentration-dependent, reversible and slow increase of [Ca²⁺]; with an EC50 of 3 nmol/liter Ang II (N = 229). Ten nmol/liter Ang II increased [Ca²⁺]_i from 41 ± 9 to 260 ± 34 nmol/liter (N = 210). In a solution with an extracellular reduced Ca²⁺ concentration of 10 µmol/liter, Ang II-mediated [Ca²⁺]_j increase was significantly reduced by 60 ± 20% (N = 12), indicating that the [Ca²⁺]_i increase was due to a Ca²⁺ influx from the extracellular space and a release of Ca²⁺ from intracellular stores. Flufenamate, an inhibitor of non-selective ion channels, significantly inhibited Ang II-mediated increase of [Ca²⁺]_i (IC50 = 20 µmol/liter, N = 29), whereas the L-type Ca²⁺ channel blocker nicardipine even in high concentrations of > 1 µmol/liter had only a small inhibitory effect. The AT₁ receptor antagonist losartan inhibited Ang II-mediated [Ca²⁺]_i increase with an IC₅₀ of about 0.3 nmol/liter (N = 35). The data suggest that Ang II increases [Ca²⁺]_i in podocytes by an influx of Ca²⁺ through non-selective channels and by a release of Ca²⁺ from intracellular stores. The effect of Ang II is mediated via an AT₁ receptor.