Regulation of Glomerular Ultrafiltration by Glomerular Epithelial Cells

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Glomerular filtration is defined by glomerular ultrafiltration pressure and ultrafiltration coefficicnt. The former has been shown to be regulated by constriction or relaxation of the glomerular afferent and efferent arteries, however how the ultrafiltration is controled in the glomerulus has not been clarified yet. Atrial natriuretic peptide (ANP) is a hormone which facilitates diuresis and natriuresis by increasing the ultrafiltration coefficient and subsequently the glomerular filtration rate and by suppressing sodium reabsorption from collecting ducts. To elucidate glomerular cells which play a role on regulation of glomerular ultrafiltration, mRNA for natriuretic peptide receptors was localized in the kidney by ribonucleasc protection assay and in situ hybridization. Ribonuclease protection assay and in situ hybridization showed that the glomerular epithelial cells have mRNA for type A and type C ANP reccptor subtypes. Since type A receptors but not type C receptors have guanylate cyclase domain in the cytoplasmic region, ANP is predicted to excite the glomerular epithelial cells through binding to the type A receptors and to mediate the increase of ultrafiltration coefficient.The immunological injury of the glomerular epithelial cells by an in vivo administration of a specific antibody in rats distorted the glomerular filtration function such as glomcrular ultrafiltration coefficient. Morphometric analysis revealed no alterations except an increase in the volume of glomerular cpithclial cclls after the immune injury of these cells. In turn, the ultrafiltration coeffieient decreased when mesangial cells were damaged by in vivo administration of another antibody against these cells. These results indicate that the glomerular cpithclial cells play an important role in the regulation of glomerular filtration through changing ultrafiltration coefficient which might be also regulated by mesangial cells as well.