A key role for podocytes in the pathogenesis of proteinuric renal diseases has been established. Angiotensin II causes depolarization and increased intracellular calcium concentration in podocytes; members of the cation TRPC channels family, particularly TRPC6, are proposed as proteins responsible for calcium flux. Angiotensin II evokes calcium transient through TRPC channels and mutations in the gene encoding the TRPC6 channel result in the development of focal segmental glomerulosclerosis. Here we examined the effects of angiotensin II on intracellular calcium ion levels and endogenous channels in intact podocytes of freshly isolated decapsulated mouse glomeruli. An ion channel with distinct TRPC6 properties was identified in wild type, but was absent in TRPC6 knockout mice. Single channel electrophysiological analysis found that angiotensin II acutely activated native TRPC-like channels in both podocytes of freshly isolated glomeruli and TRPC6 channels transiently overexpressed in CHO cells; the effect was mediated by changes in the channel open probability. Angiotensin II evoked intracellular calcium transients in the wild type podocytes, which was blunted in TRPC6 knockout glomeruli. Pan-TRPC inhibitors gadolinium and SKF 96365 reduced the response in wild type glomerular epithelial cells, whereas the transient in TRPC6 knockout animals was not affected. Thus, angiotensin II-dependent activation of TRPC6 channels in podocytes may have a significant role in the development of kidney diseases.

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Membrane cholesterol and lipid rafts are implicated in various signalling processes involving actin rearrangement in living cells. However, functional link between raft integrity and organisation of cytoskeleton remains unclear. We have compared the effect of cholesterol sequestration on F-actin structures in normal and transformed fibroblasts in which microfilament system is developed to a different extent. The depletion of membrane cholesterol by methyl-beta-cyclodextrin (MbCD) resulted in a disruption of lipid rafts in plasma membrane as it was revealed by fluorescent labelling of GM1 ganglioside. In normal fibroblasts with highly developed microfilament system, the cholesterol depletion resulted in actin disassembly and reduction of stress fibres. However, in transformed cells containing low amount of fibrillar actin, MbCD treatment induced intensive formation of stress fibres and increased cell spreading. The results show that the effect of cholesterol depletion and lipid raft disruption on microfilament system is critically determined by the initial state of cytoskeleton, specifically, by the balance of polymerised and monomeric actin in the cell. We assume that uncapping of the microfilaments is the key step of cholesterol-regulated actin remodelling.