Lactate transport in insulin-secreting beta-cells: contrast between rat islets and HIT-T15 insulinoma cells.
The transport of L- and D-lactate into rat pancreatic islets and HIT-T15 insulinoma cells was studied by measuring uptake of 14C-labelled substrate at room temperature and by following changes in intracellular pH (pHi) in islets and HIT-T15 cells loaded with 2',7'-bis(carboxyethyl)-5'(6')-carboxyfluorescein (BCECF). Uptake of L-lactate into HIT-T15 cells was rapid, reaching equilibrium after 5 min with an apparent Km value of 4.8 mM. Transport was markedly inhibited by alpha-cyano-4-hydroxycinnamate, alpha-fluorocinnamate, quercetin and p-chloromercuribenzenesulphonate (pCMBS), and was enhanced in citrate medium. Uptake of D-lactate was less rapid, apparent equilibrium not being reached within 10 min. In contrast to HIT-T15 cells, rat pancreatic islets showed greatly reduced rates of transport of L- and D-lactate together with a correspondingly lower degree of inhibition by alpha-cyano-4-hydroxycinnamate. The addition of L- or D-lactate to HIT-T15 cells, but not dispersed islet cells, resulted in a marked and rapid intracellular acidification followed by a gradual recovery. In both HIT-T15 cells and isolated islets, the rates of transport of both L- and D-lactate in the presence of alpha-cyano-4-hydroxycinnamate were significantly greater in a depolarising K+ medium compared to the normal Na+ medium. These observations suggest that native rat islet cells have considerably reduced activity of the lactate-/H+ transport system compared to HIT-T15 insulinoma cells. There is evidence in both cell types of an additional electrogenic pathway for lactate which might play a role in coupling lactate efflux to beta-cell depolarisation.
Best
L
L
Department of Physiological Sciences, University of Manchester, Manchester Royal Infirmary, UK.
Trebilcock
R
R
Tomlinson
S
S
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D003373:Coumaric Acids / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007340:Insulinoma / Q000378:metabolism* / Q000473:pathology; D007515:Islets of Langerhans / Q000378:metabolism*; D007773:Lactates / Q000493:pharmacokinetics*; D019344:Lactic Acid; D027501:Monocarboxylic Acid Transporters; D010190:Pancreatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D011794:Quercetin / Q000494:pharmacology; D051381:Rats; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D002352:Carrier Proteins; D003373:Coumaric Acids; D007328:Insulin; D007773:Lactates; D027501:Monocarboxylic Acid Transporters; C007175:alpha-cyano-4-hydroxycinnamate; D019344:Lactic Acid; D002731:4-Chloromercuribenzenesulfonate; D000584:Amiloride; D011794:Quercetin