TY - JOUR
T1 - Modulation of monocarboxylic acid transporter-1 kinetic function by the cAMP signaling pathway in rat brain endothelial cells
AU - Smith, Jeffrey P.
AU - Drewes, Lester R
PY - 2006/1/27
Y1 - 2006/1/27
N2 - MCT1 (monocarboxylic acid transporter 1) facilitates bidirectional monocarboxylic acid transport across membranes. MCT1 function and regulation have not been characterized previously in cerebral endothelial cells but may be important during normal cerebral energy metabolism and during brain diseases such as stroke. Here, by using the cytoplasmic pH indicator 2′,7′- bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-acetoxymethyl ester, the initial rates of monocarboxylate-dependent cytoplasmic acidification were measured as an indication of MCT1 kinetic function in vitro using the rat brain endothelial cell (RBE4) model of blood-brain transport. The initial rate of L-lactate-dependent acidification was significantly inhibited by 5-10-min incubations with agonists of intracellular cAMP-dependent cell signaling pathways as follows: dibutyryl cAMP, forskolin, and isoproterenol. Isoproterenol reduced Vmax but did not affect Km values. The effects of forskolin were completely reversed by the protein kinase A inhibitor H89, whereas H89 alone increased transport rates. Cytoplasmic cAMP levels, measured by radioimmunoassay, were increased by forskolin or isoproterenol, and the effect of isoproterenol was inhibited by propranolol. MCT1-independent intracellular pH control mechanisms did not contribute to the forskolin or H89 effects on MCT1 kinetic function as determined with amiloride, monocarboxylate-independent acid loading, or the transport inhibitor α-cyano-4-hydroxycinnamate. The data demonstrate the direct modulation of MCT1 kinetic function in cerebral endothelial cells by agents known to affect the β-adrenergic receptor/adenylyl cyclase/cAMP/protein kinase A intracellular signaling pathway.
AB - MCT1 (monocarboxylic acid transporter 1) facilitates bidirectional monocarboxylic acid transport across membranes. MCT1 function and regulation have not been characterized previously in cerebral endothelial cells but may be important during normal cerebral energy metabolism and during brain diseases such as stroke. Here, by using the cytoplasmic pH indicator 2′,7′- bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-acetoxymethyl ester, the initial rates of monocarboxylate-dependent cytoplasmic acidification were measured as an indication of MCT1 kinetic function in vitro using the rat brain endothelial cell (RBE4) model of blood-brain transport. The initial rate of L-lactate-dependent acidification was significantly inhibited by 5-10-min incubations with agonists of intracellular cAMP-dependent cell signaling pathways as follows: dibutyryl cAMP, forskolin, and isoproterenol. Isoproterenol reduced Vmax but did not affect Km values. The effects of forskolin were completely reversed by the protein kinase A inhibitor H89, whereas H89 alone increased transport rates. Cytoplasmic cAMP levels, measured by radioimmunoassay, were increased by forskolin or isoproterenol, and the effect of isoproterenol was inhibited by propranolol. MCT1-independent intracellular pH control mechanisms did not contribute to the forskolin or H89 effects on MCT1 kinetic function as determined with amiloride, monocarboxylate-independent acid loading, or the transport inhibitor α-cyano-4-hydroxycinnamate. The data demonstrate the direct modulation of MCT1 kinetic function in cerebral endothelial cells by agents known to affect the β-adrenergic receptor/adenylyl cyclase/cAMP/protein kinase A intracellular signaling pathway.
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U2 - 10.1074/jbc.M511577200
DO - 10.1074/jbc.M511577200
M3 - Article
C2 - 16301311
AN - SCOPUS:33644849615
SN - 0021-9258
VL - 281
SP - 2053
EP - 2060
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 4
ER -