Studies of the mechanism of activation of HIT-T15 cells by lactate.
L-Lactate, D-lactate, propionate and acetate (all 20 mM) caused a marked intracellular acidification in HIT-T15 cells loaded with 2'7'-bis(carboxyethyl)-5'(6')-carboxyfluorescein (BCECF), followed by recovery to more alkaline values. The effects of L- and D-lactate, but not propionate or acetate, were inhibited by 5 mM alpha-fluorocinnamate. Both L- and D-lactate caused a marked depolarisation and rise in cytosolic [Ca2+] in HIT cells as assessed by oxonol-V and quin2 fluorescence, respectively. Propionate had similar, though less marked, effects, whereas acetate exerted only a modest influence on membrane potential and cytosolic [Ca2+]. The rate of oxidation of L-lactate by HIT cells greatly exceeded that of D-lactate. alpha-Fluorocinnamate delayed, but did not prevent, the effects of L-lactate on HIT cell membrane potential or cytosolic [Ca2+]. L-lactate diminished the rate of efflux of 86Rb+ from preloaded HIT cells. Inhibition of calcium- and nucleotide-sensitive K+ channels with tetraethylammonium and tolbutamide also reduced the 86Rb+ efflux rate, and prevented any further reduction in response to L-lactate. However, such inhibition of K+ channels did not prevent a further depolarisation and rise in cytosolic [Ca2+] upon the subsequent addition of lactate. It is suggested that the activation of HIT-T15 cells by lactate is not the result of intracellular acidification or increased metabolic flux, and does not require diminished K+ permeability. An alternative mechanism is based upon the possible electrogenic flux of lactate across the plasma membrane.
Lynch
A M
AM
Department of Medicine, University of Manchester, U.K.
Trebilcock
R
R
Tomlinson
S
S
Best
L
L
D000085:Acetates / Q000494:pharmacology; D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005452:Fluoresceins; D006863:Hydrogen-Ion Concentration; D007340:Insulinoma / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism*; D007555:Isoxazoles; D007773:Lactates / Q000494:pharmacology*; D019344:Lactic Acid; D008564:Membrane Potentials; D011422:Propionates / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000085:Acetates; D000634:Aminoquinolines; D005452:Fluoresceins; D007555:Isoxazoles; D007773:Lactates; D011422:Propionates; D019344:Lactic Acid; C013633:oxonol V; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; C035739:Quin2; D002118:Calcium