Functional characterisation of the volume-sensitive anion channel in rat pancreatic beta-cells

The whole-cell and perforated patch configurations of the patch-clamp techn ique were used to characterise the volume-sensitive anion channel in rat pa ncreatic beta -cells. The channel showed high permeability (P) relative to Cl- to extracellular monovalent organic anions (P-SCN/P-Cl = 1.73, P-acetat e/P-Cl = 0.39, Pl(actate)/P-Cl = 0.38, P-acetoacetate/P-Cl = 0.32, P-glutam ate/P-Cl = 0.28) but mas less permeable to the divalent anion malate (P-mal ate/P-Cl = 0.14). Channel activity was inhibited by a number of putative an ion channel inhibitors, including extracellular ATP (10 mM), 1,9-dideoxyfor skolin (100 mum) and 4-OH tamoxifen (10 muM). Inclusion Of the catalytic su bunit of protein kinase,4 in the pipette solution did not activate the volu me-sensitive anion channel in non-swollen cells. Furthermore, addition of 8 -bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) or forskolin failed t o activate the channel in intact cells under perforated patch conditions. A ddition of phorbol 12,13-dibutyrate (200 nM), either before or after cell s welling, also failed to affect channel activation. Our findings do not supp ort the suggestion that the volume-sensitive anion channel in pancreatic be ta -cells can be activated by protein kinase A. Furthermore, the beta -cell channel does not appear to be subject to regulation via protein kinase C.