Differential regulation of [Ca2+]i oscillations in mouse pancreatic islets by glucose, alpha-ketoisocaproic acid, glyceraldehyde and glycolytic intermediates.
Glucose induces slow oscillations of the cytoplasmic Ca2+ concentration in pancreatic beta-cells. In order to elucidate the mechanisms responsible for the slow [Ca2+]i oscillations the effects of various nutrient insulin secretagogues on glucose-induced [Ca2+]i oscillations in intact mouse pancreatic islets and single beta-cells were studied. These were the glycolytic intermediates, glyceraldehyde and pyruvate, and the mitochondrial substrate, alpha-ketoisocaproic acid (KIC). Glucose, at a 10 or 15 mM concentration, induced the typical slow oscillations of [Ca2+]i (0.4 min(-1)). At higher glucose concentrations the frequency of these oscillations decreased further (0.2 min(-1)). Glyceraldehyde, an insulin secretagogue like glucose, did not cause slow oscillations of [Ca2+]i in the absence of glucose. However, it exhibited a synergistic action with glucose. Glyceraldehyde, at 3 or 10 mM concentration, induced slow [Ca2+]i oscillations at a substimulatory concentration of 5 mM glucose (0.3-0.4 min(-1)) and reduced the frequency of the glucose-induced [Ca2+]i oscillations at stimulatory concentrations of 10 or 15 mM glucose (0.2 min(-1)). KIC (5 or 10 mM) as well as pyruvate (10 mM), the end product of glycolysis, and its ester methyl pyruvate (10 mM), did not cause slow oscillations of [Ca2+]i in the absence of glucose. In contrast to glyceraldehyde, however, all three compounds were capable of preventing the slow [Ca2+]i oscillations induced by glucose. Mannoheptulose (2 mM), an inhibitor of glucokinase and glucose-induced insulin secretion, reversibly blocked any kind of [Ca2+]i oscillation and returned the [Ca2+]i to a basal level through its ability to inhibit glycolytic flux. It can be concluded therefore that only substrates which generate a glucokinase-mediated metabolic flux through glycolysis and produce glycolytic ATP can induce slow [Ca2+]i oscillations in pancreatic beta-cells.
Lenzen
S
S
Institute of Clinical Biochemistry, Hannover Medical School, Germany.
Lerch
M
M
Peckmann
T
T
Tiedge
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D005985:Glyceraldehyde / Q000494:pharmacology*; D006019:Glycolysis; D007515:Islets of Langerhans / Q000187:drug effects / Q000502:physiology*; D007651:Keto Acids / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D008815:Mice, Inbred Strains; D009991:Oscillometry; D011773:Pyruvates / Q000494:pharmacology
D007651:Keto Acids; D011773:Pyruvates; D005985:Glyceraldehyde; C013082:alpha-ketoisocaproic acid; D005947:Glucose; D002118:Calcium