Involvement of guanine nucleotide and sodium in regulation of yohimbine and clonidine binding sites in the HT29 human colon adenocarcinoma cell-line

Demonstration of functional receptors for noradrenaline and adenosine-5'-triphosphate, but not for prostaglandin E2, in HT-29 human colon cancer cell line

1. The aim of the current study was to investigate in HT-29 human colon cancer cell line, the existence of functional receptors for the signalling molecules, noradrenaline (NA), prostaglandin E2 (PGE2), and adenosine-5'-triphosphate (ATP). 2. We utilized microphysiometry, which monitors on-line extracellular acidification rate (ECAR) as a measure of cellular metabolic activity, and how this variable is altered by signalling molecules. 3. Challenge with NA (5.9 microM) resulted in an increase in ECAR by approximately 24% of basal. 4. PGE2 (0.0284, 0.284 and 2.84 microM) hardly affected ECAR. 5. ATP (100 microM) elicited a biphasic effect on ECAR (increase and decrease in ECAR by about 58 and 10% of basal, respectively). 6. HT-29 cells were shown to express COX-2 by immunocytochemistry. 7. These data suggest the presence of functional receptors for NA and ATP, but not for PGE2 in HT-29 human colon cancer cell line.

Characterization of Na+/K+/Cl- cotransport in cultured HT29 human colonic adenocarcinoma cells

A Na+/K+/Cl- cotransport pathway has been examined in the HT29 human colonic adenocarcinoma cell line using 86Rb as the K congener. Ouabain-resistant bumetanide-sensitive (OR-BS) K+ influx in attached HT29 cells was 17.9 +/- 0.9 nmol/min per mg protein at 25 degrees C. The identity of this pathway as a Na+/K+/Cl- cotransporter has been deduced from the following findings: (a) OR-BS K+ influx ceased if the external Cl- (Cl-o) was replaced by NO3- or the external Na+ (Na+o) by choline; (b) neither OR-BS 24Na+ nor 36Cl- influx was detectable in the absence of external K+ (K+o); and (c) concomitant measurements of 86Rb+, 22Na+, and 36Cl- influx indicated that the stoichiometry of the cotransport system approached a ratio of 1N+:1K+:2Cl-. In addition, OR-BS K+ influx was exquisitely sensitive to cellular ATP levels. Depletion of the normal ATP content of 35-40 nmol/mg protein to 10-15 nmol/mg protein, a concentration at which the ouabain-sensitive K+ influx was unaffected, completely abolished K+ cotransport. OR-BS K+ influx was slightly reduced by the divalent cations Ca2+, Ba2+, Mg2+ and Mn2+. Although changes in cell volume, whether shrinking or swelling, did not influence OR-BS K+ influx, ouabain-sensitive K+ influx was activated by cell swelling. As in T84 cells, we found that the OR-BS K+ influx in HT29 cells was stimulated by exogenous cyclic AMP analogues and by augmented cyclic AMP content in response to vasoactive intestinal peptide, forskolin, norepinephrine and forskolin or prostaglandin E1.