Background: Sulfonylurea agents exert their physiologic effects via binding to specific sulfonylurea receptors (SUR) in adenosine triphosphate-sensitive potassium (K(ATP)) channels. Mesangial cells express K(ATP) and respond to sulfonylureas by altering glucose metabolism, elevating intracellular calcium and contracting. A putative endogenous sulfonylurea, alpha-endosulfine, has been demonstrated in diverse tissues and is a member of the cyclic adenosine monophosphate (cAMP)-regulated family of phosphoproteins. This study investigates mesangial cell expression of ENSA, the gene encoding alpha-endosulfine, and its regulation by glucose.
Methods: Expression of rat glomerular and mesangial ENSA was examined by reverse transcription-polymerase chain reaction (RT-PCR) and Northern analysis. In situ hybridization studies were carried out to investigate the presence and distribution of ENSA in kidney cortex. Expression of mesangial cell alpha-endosulfine was studied by immunoblotting, immunofluorescence, and confocal microscopy.
Results: RT-PCR with gene-specific primers and Northern blotting disclosed abundant expression of two major ENSA transcripts at 2.4 kb and 1.2 kb in whole rat kidney, kidney cortex, and mesangial cells. In situ hybridization of rat kidney demonstrated renal ENSA expression, particularly within glomeruli. Confocal microscopy revealed a diffusely granular, cytosolic distribution of alpha-endosulfine. High glucose concentrations increased ENSA expression by 24 hours, an effect that persisted for at least 10 days. Protein expression paralleled gene expression.
Conclusion: ENSA and alpha-endosulfine are expressed in rat glomeruli and mesangial cell and gene and protein expression are up-regulated by a high glucose environment. alpha-Endosulfine has potential roles as a regulator of metabolism and contractility via mesangial cell K(ATP).