HCO(3)(−)-dependent volume regulation in α-cells of the rat endocrine pancreas

Ion transport activity in pancreatic α-cells was assessed by studying cell volume regulation in response to anisotonic solutions. Cell volume was measured by a video imaging method, and cells were superfused with either 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid-buffered or HCO(3)(−)-buffered solutions. α-Cells did not exhibit a regulatory volume increase (RVI) in response to cell shrinkage caused by hypertonic solutions. A RVI was observed, however, in cells that had first undergone a regulatory volume decrease (RVD), but only in HCO(3)(−)-buffered solutions. RVI was also observed in response to a HCO(3)(−)-buffered hypertonic solution in which the glucose concentration was increased from 4 to 20 mM. The post-RVD RVI and the glucose-induced RVI were both inhibited by 10 μM 5-(N-methyl-N-isobutyl) amiloride or 100 μM 2,2′-(1,2-ethenediyl) bis (5-isothio-cyanatobenzenesulfonic acid), but not by 10 μM benzamil nor 10 μM bumetanide. These data suggest that Na(+)–H(+) exchangers and Cl(−)–HCO(3)(−) exchangers contribute to volume regulation in α-cells.