Microfluorometric analysis of Cl- permeability and its relation to oscillatory Ca2+ signalling in glucose-stimulated pancreatic β-cells

The cytoplasmic concentrations of Cl-([Cl-](i)) and Ca2+ ([Ca2+](i)) were measured with the fluorescent indicators N-(ethoxycarbonylmethyl)-6-methoxyquinilinum bromide (MQAE) and fura-2 in pancreatic beta -cells isolated from ob/ob mice. Steady-state [Cl-](i) in unstimulated beta -cells was 34 mM, which is higher than expected from a passive distribution. Increase of the glucose concentration from 3 to 20 mM resulted in an accelerated entry of Cl- into p-cells depleted of this ion. The exposure to 20 mM glucose did not affect steady-state [Cl-](i) either in the absence or presence of furosemide inhibition of Na+, K+, 2 Cl- co-transport. Glucose-induced oscillations of [Ca2+](i) were transformed into sustained elevation in the presence of 4,4' diisothiocyanato-dihydrostilbene-2,2'-disulfonic acid (H2DIDS). A similar effect was noted when replacing 25% of extracellular Cl- with the more easily permeating anions SCN-, I-, NO3- or Br-. It is concluded that glucose stimulation of the beta -cells is coupled to an increase in their Cl- permeability and that the oscillatory Ca2+ signaling is critically dependent on transmembrane Cl- fluxes. (C) 2000 Elsevier Science Inc. All rights reserved.