Characterization of the rat mesangial cell type 2 sulfonylurea receptor

Sulfonylurea receptors are classified as either high-affinity type 1 (SUR1) or low-affinity type 2 receptors (SUR2), and the gene expression of SURs has recently been demonstrated in kidney. However, functional data regarding a renal SUR are lacking. We previously demonstrated that mesangial cell (MC) gene and protein expression of extracellular matrix components were up-regulated by the sulfonylurea, tolazamide. After noting this biological response, we next sought to investigate the presence of a sulfonylurea receptor in rat MCs.

Equilibrium binding studies employing [3H]glibenclamide as a ligand were performed on crude MC membrane preparations. Gene expression for SUR was explored by Northern analysis of cultured MCs and whole kidney tissue. The effect of sulfonylurea on intracellular Ca2+ in MCs was assayed by spectrofluorometry, and glibenclamide-induced changes in the contractility of MCs were assessed.

MCs bound [3H]glibenclamide with a KD of 2.6 microM and a Bmax of 30.4 pmol/mg protein as determined by Scatchard analysis. Three SUR2 transcripts were detected in MCs. A major transcript was detected at 5.5 kb and minor transcripts at 7.5 and 8.6 kb. Following sulfonylurea treatment of MCs, real-time videomicroscopy revealed intense MC contraction, coinciding with oscillatory increments of intracellular Ca2+ concentration. Further evidence of sulfonylurea-induced MC contraction was demonstrated by glibenclamide-induced deformation of a silicone rubber substrate.

These results demonstrate that SUR2 resides on MCs. Functional activation of this receptor by sulfonylurea induces Ca2+ transients that result in MC contraction.