摘要
Mechanosensitive large-conductance Ca 2+ -activated K + channels encoded by the Slo1 gene (BK Ca channels) are expressed in podocytes. Here we show that BK Ca channels reciprocally coimmunoprecipitate with synaptopodin (Synpo) in mouse glomeruli, in mouse podocytes, and in a heterologous expression system (HEK293T cells) in which these proteins are transiently expressed. Synpo and Slo1 colocalize along the surface of the glomerular basement membrane in mouse glomeruli. Synpo interacts with BK Ca channels at COOH-terminal domains that overlap with an actin-binding domain on the channel molecule that is necessary for trafficking of BK Ca channels to the cell surface. Moreover, addition of exogenous β-actin to mouse podocyte lysates reduces BK Ca -Synpo interactions. Coexpression of Synpo increases steady-state surface expression of BK Ca channels in HEK293T cells. However, Synpo does not affect the stability of cell surface BK Ca channels, suggesting a primary effect on the rate of forward trafficking, and Synpo coexpression does not affect BK Ca gating. Conversely, stable knockdown of Synpo expression in mouse podocyte cell lines reduces steady-state surface expression of BK Ca channels but does not affect total expression of BK Ca channels or their gating. The effects of Synpo on surface expression of BK Ca are blocked by inhibition of Rho signaling in HEK293T cells and in podocytes. Functional cell surface BK Ca channels in podocytes are also reduced by sustained (2 h) but not acute (15 min) depolymerization of actin with cytochalasin D. Synpo may regulate BK Ca channels through its effects on actin dynamics and by modulating interactions between BK Ca channels and regulatory proteins of the podocyte slit diaphragm. Copyright © 2010 The American Physiological Society.