title: Lactate transport in freshly isolated human fetal retinal pigment epithelium.
abstract: OBJECTIVE
  To study transport mechanisms for small monocarboxylic acids in the apical and basolateral membranes of freshly isolated, human fetal retinal pigment epithelium.
  
  
  METHODS
  The epithelium was mounted in a small Ussing chamber that allowed separate perfusion of both the apical and basal compartments and simultaneous measurements of intracellular pH, transepithelial potential, and tissue resistance. Intracellular pH was measured using a pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein.
  
  
  RESULTS
  When 10-100 mM lactate or pyruvate was added to the apical bath the cells acidified by 0.10-0.25 pH units. There were no differences between the initial rates of intracellular acidification produced by L-lactate and D-lactate. These rates could be described as Michaelis-Menten functions of the concentrations of lactate and pyruvate. The Km values were 42 +/- 12 mM for L-lactate and 34 +/- 8 mM for pyruvate. The rates of acidification caused by 50 mM L-lactate were reversibly reduced by 44% or 35% after apical administration of probenecid (2 mM) or alpha-cyano-4-hydroxycinnamate (2 mM), and irreversibly reduced by 78% after apical administration of the sulfhydryl-reagent mersalyl acid (2 mM). The intracellular acidifications caused by apical pyruvate (50 mM) were completely and reversibly inhibited by 50 mM apical L-lactate. Addition of 50 to 100 mM lactate to the basal bath caused intracellular alkalinizations, which could be inhibited by Na+ removal in the basal bath or by 2 mM alpha-cyano-4-hydroxycinnamate in the apical bath.
authors.affiliation: Institute for Medical Physiology, University of Copenhagen, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: la Cour
authors.forename: H
authors.initials: H
authors.lastname: Lin
authors.forename: E
authors.initials: E
authors.lastname: Kenyon
authors.forename: S S
authors.initials: SS
authors.lastname: Miller
mesh_terms: D001485:Basement Membrane / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D003373:Coumaric Acids / Q000494:pharmacology; D004594:Electrophysiology; D005333:Fetus; D005452:Fluoresceins; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000378:metabolism* / Q000494:pharmacology; D019344:Lactic Acid; D008564:Membrane Potentials; D008634:Mersalyl / Q000494:pharmacology; D027501:Monocarboxylic Acid Transporters; D010857:Pigment Epithelium of Eye / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D003373:Coumaric Acids; D005452:Fluoresceins; D007773:Lactates; D027501:Monocarboxylic Acid Transporters; C007175:alpha-cyano-4-hydroxycinnamate; D019344:Lactic Acid; D008634:Mersalyl; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein