Glucose-stimulated increase in cytoplasmic pH precedes increase in free Ca2+ in pancreatic beta-cells. A possible role for pyruvate.
The temporal relationship of glucose-induced increases in cytoplasmic pH (pHi) and cytoplasmic free Ca2+ was studied in single mouse pancreatic beta-cells and suspensions of clonal beta-cells (HIT). In both preparations of cells the increase in pHi preceded the cytoplasmic free Ca2+ increase. Therefore the alkalinization cannot be a consequence of the Ca2+ influx. A potential metabolic mechanism for the increase in pHi, involving stimulation of pyruvate transport and oxidation, was demonstrated in a model system of liver mitochondria incubated with pyruvate, ATP, and hexokinase to which glucose was then added to initiate ATP use. The involvement of this mechanism in beta-cells is suggested by the observation that the alkalinization was prevented in most cells by incubation with 3-hydroxycyanocinnamate, a mitochondrial pyruvate transport inhibitor. On the other hand, the inhibited cells exhibited normal Ca2+ responses to glucose stimulation. This indicates that neither pyruvate metabolism nor the alkalinization is of critical importance for the Ca2+ signal, though pyruvate oxidation or its metabolites may be important in downstream regulation of secretion.
Juntti-Berggren
L
L
Rolf Luft Center for Diabetes Research, Department of Endocrinology, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden.
Civelek
V N
VN
Berggren
P O
PO
Schultz
V
V
Corkey
B E
BE
Tornheim
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide / Q000032:analysis; D002999:Clone Cells; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D005452:Fluoresceins; D005456:Fluorescent Dyes; D016257:Fura-2; D005947:Glucose / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008820:Mice, Obese; D008954:Models, Biological; D011773:Pyruvates / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013997:Time Factors
D005452:Fluoresceins; D005456:Fluorescent Dyes; D011773:Pyruvates; D002245:Carbon Dioxide; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D005947:Glucose; D002118:Calcium; D016257:Fura-2