title: Effects of insulin and high glucose on mobilization of slo1 BKCa channels in podocytes.
abstract: Podocytes are dynamic polarized cells that lie on the surface of glomerular capillaries and comprise an essential component of the glomerular filtration barrier. Podocytes are affected in the earliest stages of diabetic nephropathy and insulin signaling to podocytes is essential for normal glomerular function. Large-conductance Ca(2+)-activated K(+) channels (BK(Ca) channels) encoded by the Slo1 gene are expressed in podocytes in a complex with multiple glomerular slit diaphragm proteins including nephrin, TRPC6 channels, and several different actin-binding proteins. Here we show that insulin increases cell surface expression of podocyte BK(Ca) channels, which is accompanied by a corresponding increase in the density of current flowing through these channels. Insulin stimulation of BK(Ca) channels was detectable in 15 min and required activation of both Erk and Akt signaling cascades. Exposure to high glucose (36.1 mM) for 24 h caused a marked reduction in the steady-state surface expression of BK(Ca) channels as well as of the slit diaphragm signaling molecule nephrin. High glucose treatment also abolished the stimulatory effects of insulin on BK(Ca) current density, although insulin continued to increase phosphorylation of Erk and Akt under those conditions. Therefore, in contrast to most other cell types, high glucose abrogates the effects of insulin in podocytes at relatively distal steps in its signaling pathway. Insulin stimulation of BK(Ca) channels in podocytes may prepare podocytes to adapt to changes in pressure gradients that occur during postprandial hyperfiltration.
authors.affiliation: Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5001, USA.
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Kim
authors.forename: Stuart E
authors.initials: SE
authors.lastname: Dryer
mesh_terms: D000818:Animals; D002460:Cell Line; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D050199:Podocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
chemical_list: D007328:Insulin; C465449:Kcnma1 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008565:Membrane Proteins; C113267:nephrin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D005947:Glucose