Transport function of hypothalamic tanycyte ependyma: how good is the evidence?

The effect of dibutyryl cyclic AMP on the transport of alpha-methyl-D-glucoside and alpha-aminoisobutyric acid in separated tubules and purified brush border membranes from rabbit kidney was investigated using a rapid filtration procedure. Dibutyryl cyclic AMP stimulated the uptake of alpha-methyl-D-glucoside and alpha-aminoisobutyric acid by separated renal tubules in agreement iwth prior studies utilizing renal slices (Rea, C. and Segal, S. (1973) Biochim. Biophys. Acta 311, 615--624; Weiss, I.W., Morgan, K. and Phang, J.M. (1972) J. Biol. Chem. 247, 760--764). However, in contrast to previous reports, no preincubation of the tissue with dibutyryl cyclic AMP was required for stimulation of transport to be manifest. Dibutyryl cyclic AMP stimulated oxygen consumption by separated tubules suggesting that stimulation of transport may occur by a linkage with renal oxidative metabolism. Dibutyryl cyclic AMP increased the uptake of alpha-aminoisobutyric acid into purified renal brush border membranes. However the uptakes of alpha-methyl-D-glucoside, proline, leucine and phosphate into brush border membranes were significantly inhibited.

Aminoisobutyric Acids↗

PubMed1979

Effects of 1-hydroxyethane-1,1-diphosphonate and dichloromethanediphosphonate on rabbit articular chondrocytes in culture.

Investigations were carried out to assess the effects of disodium 1-hydroxyethane-1,1-diphosphonate and disodium dichloromethanediphosphonate (compounds containing a P-C-P bond) on isolated rabbit articular chondrocytes in culture. Studies on growth behaviour showed that both diphosphonates displayed inhibitory actions, dichloromethanediphosphonate producing the larger effect. Both compounds inhibited the uptake of 2-deoxy-d-glucose, dichloromethanediphosphonate once more being the more potent of the two. The uptake of alpha-aminoisobutyrate was considerably increased by chondrocytes treated with dichloromethanediphosphonate, whereas 1-hydroxyethane-1,1-diphosphonate showed no effects. The biosynthesis of sulphated extracellular macromolecules secreted by the cells into the pericellular space as well as into the growth medium was greatly increased by dichloromethanediphosphonate but not by 1-hydroxyethane-1,1-diphosphonate. The stimulatory effect was dose-dependent. Short-term exposure of already confluent cells to dichloromethanediphosphonate as opposed to growing the cells to confluence in the presence of the diphosphonate revealed that the stimulatory effects were already evident after 24h, indicating that cell division is not necessarily required to produce the observed effects. The increment in proteoglycan synthesis was still evident with cells that were exposed continuously to the diphosphonate in primary as well as secondary culture. Pulse-chase experiments together with studies on the enzyme arylsulphatase revealed that the appearance of increased amounts of proteoglycans was the result of a stimulation in synthesis and not due to an inhibition in turnover.

Aminoisobutyric Acids↗