Functional evidence for a monocarboxylate transporter (MCT) in strial marginal cells and molecular evidence for MCT1 and MCT2 in stria vascularis
Abstract
The transport of lactate, pyruvate and other monocarboxylates across plasma membranes of metabolically active cells such as strial marginal cells (SMC) may be important under aerobic conditions as well as under ischemic and hypoxic conditions. This study addresses the question whether SMC from the gerbil contain a membrane transport mechanism for monocarboxylates. The type of transporter was identified in functional studies by monitoring uptake of monocarboxylates into SMC through measurement of the cytosolic pH (pHi) with the pH-sensitive dye 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Further, subtypes of the functionally identified transporter which are present in stria vascularis were identified as transcripts by cloning and sequencing the reverse-transcription polymerase chain reaction (RT-PCR) products. All functional experiments were performed under nominally HCO3--free conditions. The monocarboxylates acetate and pyruvate (each 20 mM) induced an acidification of pHi. In contrast, the dicarboxylate malonate (20 mM) had no significant effect on pHi. Alpha-cyano-4-hydroxycinnamate (CHC; 5 mM), a blocker of H+/monocarboxylate cotransporter (MCT), reduced reversibly the acidification induced by 5 mM pyruvate....Continue Reading
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