Active transport of thiamine by freshly isolated rat hepatocytes.

Abstract

SummaryRat hepatocytes were freshly prepared from adult animals using the collagenase-perfusion technique. The hepatic transport of thiamine was studied in isolated liver cells. The process was found to be saturable with an apparent Kt of 0.31mM and a Vmax of 0.7 umoles/ml intracellular fluid/5 minutes. However, at higher substrate concentrations, the process proceeded in a linear fashion. Both pyrithiamine and oxythiamine were inhibitory on the hepatic uptake of thiamine, the latter showed much weaker activity than the former. The system required the presence of sodium ions and was sensitive to ouabain. Anaerobic condition and metabolic inhibitors, e.g., 2,4-dinitrophenol, cyanide, and iodoacetate suppressed the uptake rate of thiamine. Addition of ethanol in the incubation medium also caused significant reduction of thiamine uptake. Efflux studies indicated that a portion of intracellular thiamine is readily available for exodus. Chromatographic analyses showed that thiamine was only slightly metabolically altered during the transport process. It is suggested that thiamine is transported into isolated hepatic cells by an active, sodium-dependent process.

Properties of thiamin transport in isolated perfused hearts of chronically alcoholic guinea pigsThis article is one of a selection of papers published in the special issue Bridging the Gap: Where Progress in Cardiovascular and Neurophysiologic Research Meet.

“…Our finding that thiamin transport in the heart is energydependent is in good agreement with the properties of thiamin uptake in other tissues, such as human retinal pigment cells (Subramanian et al 2007) or hepatocytes (Chen 1978). Taking into account our finding that thiamin transport is energy-dependent, this could explain the reduction of thiamin transport across the cellular membrane of cardiac cells of chronically alcoholic animals.…”

Thiamin Function, Metabolism, Uptake, and Transport

“…When the intestinal concentration of T + is <2 μM, however, T + is actively transported by OCTs − and ALPs . Recent studies show, however, that both active transport and passive transport of T + occur simultaneously in the same tissues and organs. , For other forms of thiamin, TPP, and TTP (which are normally not available extracellularly , ), the transfer across membranes is conducted after conversion back to the TMP and T + forms. , Once delivered to the cytosol, thiamin is metabolized to all three forms of thiamin (Figure ) in the tissues and organs, as well as the cationic form , (Figure ).…”

Cloning of the Human Thiamine Transporter, a Member of the Folate Transporter Family

“…The underlying mechanism of transplacental transport of thiamine has been investigated using in vitro perfusion techniques (3,4) as well as isolated placental brush border membrane vesicles (5). Thiamine transport has also been functionally characterized in other tissues/ cells such as intestine (6 -9), erythrocytes (10), hepatocytes (11), and neuroblastoma cells (12). These studies have shown that the transport of thiamine is a carrier-mediated, energydependent process.…”