Characterization of the rat mesangial cell type 2 sulfonylurea receptor

Background. Sulfonylurea receptors are classified as either high-affinity t ype 1 (SUR1) or low-affinity type 2 receptors (SUR2), and the gene expressi on of SURs has recently been demonstrated in kidney. However, functional da ta regarding a renal SUR are lacking. We previously demonstrated that mesan gial cell (MC) gene and protein expression of extracellular matrix componen ts were up-regulated by the sulfonylurea, tolazamide. After noting this bio logical response, we next sought to investigate the presence of a sulfonylu rea receptor in rat MCs. Methods. Equilibrium binding studies employing [H-3]glibenclamide as a liga nd were performed on crude MC membrane preparations. Gene expression for SU R was explored by Northern analysis of cultured MCs and whole kidney tissue . The effect of sulfonylurea on intracellular Ca2+ in MCs was assayed by sp ectrofluorometry, and glibenclamide-induced changes in the contractility of MCs were assessed. Results. MCs bound [H-3]glibenclamide with a KD of 2.6 mu M and a B-max of 30.4 pmol/mg protein as determined by Scatchard analysis. Three SUR2 transc ripts were detected in MCs. A major transcript was detected at 5.5 kb and m inor transcripts at 7.5 and 8.6 kb. Following sulfonylurea treatment of MCs , real-time videomicroscopy revealed intense MC contraction, coinciding wit h oscillatory increments of intracellular Ca2+ concentration. Further evide nce of sulfonylurea-induced MC contraction was demonstrated by glibenclamid e-induced deformation of a silicone rubber substrate. Conclusions. These results demonstrate that SUR2 resides on MCs. Functional activation of this receptor by sulfonylurea induces Ca2+ transients that r esult in MC contraction.