Mechanism of Angiotensin II ‐ Mediated Changes in Glomeruli Permeability and Calcium Influx in Podocytes

Abstract

Podocytes maintain glomerular structure and permeability and play a key role in the pathogenesis of various renal diseases. It was previously shown that angiotensin II (Ang II), the key peptide in the RAAS, produces an increase in intracellular Ca2+ in cultured podocytes. Members of the TRPC ion channels family were proposed to be responsible for this calcium flux. We examined here the effects of Ang II on the function of the podocytes of freshly isolated rat glomeruli using ratiometric epifluorescence calcium imaging with Fura2-AM, patch clamp electrophysiology and a novel protocol designed to measure dynamic changes in glomerular permeability to albumin. To assess the effects of Ang II on glomerular function we measured real-time albumin permeability changes using two fluorescently labeled dextrans and confocal microscopy. We found that Ang II rapidly reduced glomerular volume resulting in increased glomerular permeability to albumin. This response was attenuated by treatment with 10 µM losartan and 1 µM PD 123319, specific inhibitors of AT1 and AT2 receptors, respectively. Single channel patch-clamp analysis demonstrated that Ang II acutely activates native TRPC6 channels in the podocytes; the effect is mediated by changes in the channel Po. Depletion of internal Ca2+ stores with thapsigargin did not affect calcium influx activated by Ang II, whereas TRPC channel blocker SKF 96365 decreased this response. Overall, our data indicate that Ang II induces glomeruli albumin permeability changes likely via both AT1 and AT2 receptors, and Ang II-dependent activation of calcium influx in podocytes might play a significant role in the pathogenesis of kidney diseases via effects on glomeruli permeability.