Intestinal transport of thiamin and thiamin monophosphate in rat everted jejunal sacs: a comparative study using some potential inhibitors.
Rat everted jejunal sacs were incubated for 15 and 30 min at 37 degrees C in oxygenated Krebs-Henseleit buffer, pH 7.4, containing 0.2 microM [3H]-thiamin (3H-T) or [3H]-thiamin monophosphate (3H-TMP) with and without 10 mM 1-phenylalanine (PAL) or 2.5 mM levamisole (LEV). The concentrations of 3H-T and its phosphoesters in sac wall and serosal fluid were determined by a radiometric method after electrophoretic separation. In separate experiments, thiamin pyrophosphokinase (TPKase) and thiamin pyrophosphatase (TPPase) activities were determined in mucosal scrapings, with and without PAL or LEV, by using a radiometric and a colorimetric method, respectively. 3H-TMP was transported partly unchanged by an active mechanism similarly to 3H-T, but less efficiently. During transport, 3H-TMP was also enzymatically transformed to thiamin (T) and thiamin pyrophosphate, which accumulated in the tissue. In the serosal fluid, the concentration of 3H-TMP exceeded that of 3H-T. Presence of PAL or LEV with 3H-T or 3H-TMP in the incubation medium reduced the serosal transport and the tissue content of T compounds. LEV caused a dose-dependent inhibition of TPKase without affecting TPPase, whereas PAL inhibited both activities to about the same extent. These results indicate that the transport of TMP involves a number of different processes similar to those responsible for T transport. The effects of PAL and LEV underline the importance of phosphorylation-dephosphorylation coupling.
Gastaldi
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G
Istituto di Fisiologia umana, Università di Pavia, Italy.
Casirola
D
D
Patrini
C
C
Ricci
V
V
Laforenza
U
U
Ferrari
G
G
Rindi
G
G
D000818:Animals; D001711:Biotransformation; D005260:Female; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D007583:Jejunum / Q000378:metabolism; D007978:Levamisole / Q000494:pharmacology; D008297:Male; D010649:Phenylalanine / Q000494:pharmacology; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D013836:Thiamin Pyrophosphokinase / Q000378:metabolism; D013831:Thiamine / Q000031:analogs & derivatives* / Q000378:metabolism*; D013833:Thiamine Monophosphate / Q000378:metabolism* / Q000494:pharmacology; D013834:Thiamine Pyrophosphatase / Q000378:metabolism
D007978:Levamisole; D010649:Phenylalanine; D013833:Thiamine Monophosphate; D013836:Thiamin Pyrophosphokinase; D013834:Thiamine Pyrophosphatase; D013831:Thiamine