Expression of K +–Cl − cotransporters in the α-cells of rat endocrine pancreas

Abstract

The expression of K +–Cl − cotransporters (KCC) was examined in pancreatic islet cells. mRNA for KCC1, KCC3a, KCC3b and KCC4 were identified by RT-PCR in islets isolated from rat pancreas. In immunocytochemical studies, an antibody specific for KCC1 and KCC4 revealed the expression of KCC protein in α-cells, but not pancreatic β-cells nor δ-cells. A second antibody which does not discriminate among KCC isoforms identified KCC expression in both α-cell and β-cells. Exposure of isolated α-cells to hypotonic solutions caused cell swelling was followed by a regulatory volume decrease (RVD). The RVD was blocked by 10 μM [dihydroindenyl-oxy] alkanoic acid (DIOA; a KCC inhibitor). DIOA was without effect on the RVD in β-cells. NEM (0.2 mM), a KCC activator, caused a significant decrease of α-cell volume, which was completely inhibited by DIOA. By contrast, NEM had no effects on β-cell volume. In conclusion, KCCs are expressed in pancreatic α-cells and β-cells. However, they make a significant contribution to volume homeostasis only in α-cells.