GLUCOSE-STIMULATED INCREASE IN CYTOPLASMIC PH PRECEDES INCREASE IN FREE CA2-CELLS - A POSSIBLE ROLE FOR PYRUVATE( IN PANCREATIC BETA)

The temporal relationship of glucose-induced increases in cytoplasmic pH (pH(i)) and cytoplasmic free Ca2+ was studied in single mouse pancr eatic beta cells and suspensions of clonal beta-cells (HIT). In both p reparations of cells the increase in pH(i) preceded the cytoplasmic fr ee Ca2+ increase. Therefore the alkalinization cannot be a consequence of the Ca2+ influx. A potential metabolic mechanism for the increase in pH(i), involving stimulation of pyruvate transport and oxidation, w as demonstrated in a model system of liver mitochondria incubated with pyruvate, ATP, and hexokinase to which glucose was then added to init iate ATP use. The involvement of this mechanism in beta-cells is sugge sted by the observation that the alkalinization was prevented in most cells by incubation with 3-hydroxycyanocinnamate, a mitochondrial pyru vate transport inhibitor. On the other hand, the inhibited cells exhib ited normal Ca2+ responses to glucose stimulation. This indicates that neither pyruvate metabolism nor the alkalinization is of critical imp ortance for the Ca2+ signal, though pyruvate oxidation or its metaboli tes may be important in downstream regulation of secretion.