Photochemical labeling of the cytoplasmic surface of the membranes of intact human erythrocytes

N-(4-azido-2-nitrophenyl)-2-aminoethyl sulfonate (NAP-taurine), a photolabile nitrene precursor, has been shown to permeate the human erythrocyte membrane at 37degrees but not at 0 degrees. Utilizing this differential permeability, we have loaded intact erythrocytes with NAP-[35S]taurine in the dark at 37degrees, cooled them to 0 degrees, washed them free of external NAP-[35S]taurine in the dark and cold, and photolyzed them, resulting in labeling of hemoglobin and of proteins on the cytoplasmic surface of the membrane. These experiments complement those previously reported on the labeling of the external surface of the membranes with this reagent (Staros, J. V., and Richards, F. M. (1974) Biochemistry 13, 2720-2726).

Inhibition of plaque growth with taurolin, vantocil and amine fluoride

16 dental students rinsed daily with a placebo solution, Taurolin 2% (formaldehyde releasing antimicrobial), Vantocil 0.1% (polybiguanide), and with amine fluoride 0.025%. Depression of plaque growth assess with the Sulcular Plaque Index was 50.6, 40.2 and 21.5%, respectively.

Bile salt alteration of ion transport across jejunal mucosa

The effect of conjugated dihydroxy and trihydroxy bile salts on electrolyte transport across isolated rabbit jejunal mucosa was studied. Both taurochenodeoxycholic acid and taurocholic acid increased the short-circuit current (Isc) in bicarbonate-Ringer solution but not in a bicarbonate-free, chloride-free solution. Taurochenodeoxycholic acid was significantly more effective than taurocholic acid in increasing Isc. The presence of theophylline prevented the taurochenodeoxycholic acid- and taurocholic acid-induced increase in Isc. Transmural ion fluxes across jejunal mucosa demonstrated that 2 mM taurochenodeoxycholic acid decreased net Na+ absorption, increased net Cl- secretion and increased the residual flux (which probably represents HCO3- secretion). These studies support the hypothesis that cyclic AMP may be a mediator of intestinal electrolyte secretion.

Metabolism of lithocholate in healthy man. II. Enterohepatic circulation

Studies were carried out in healthy subjects to characterize the enterohepatic circulation of lithocholate and its metabolites. When mixed with bile and infused into the jejunum, radiolabeled lithocholylglycine was absorbed more rapidly and more efficiently than sulfolithocholylglycine, based on recovery from bile. When these metabolites were administered at 1800 hr in a liquid test meal containing radiolabeled taurocholate as an absorbable marker, 60% of lithocholylglycine was conserved, based on recovery of radioactivity in fasting bile the following morning, but only 20% of sulfolithocholylglycine was conserved. Iotope dilution studies in 4 subjects showed that daily input of lithocholate into the bile acid pool averaged 100 mg per day, about one-third to one-half of the chenodeoxycholic acid synthesis, but the t 1/2 was extremely short (0.74 day). The small lithocholate pool (about 100 mg) could be explained by rapid fecal excretion caused by sulfation which decreases passive absorption in the jejunum and active absorption in the ileum. Experiments with [35S]sulfo- [3H]lithocholylglycine indicated little desulfation during enterohepatic cycling but rapid desulfation in the distal intestine, with absorption of 35S (presumably as sulfate) followed by urinary excretion. A decreasing 35S:3H ratio in bile indicated that some steroid moiety was conserved to be resulfated. These studies indicate that considerable lithocholate is absorbed from the distal intestine in healthy subjects but efficient sulfation results in rapid fecal excretion, so that the total lithocholate pool remains small. A multicompartment model, previously used to describe the metabolism of the steroid and amino acid moieties of the major conjugated biliary bile acids, was extended to encompass lithocholyl conjugates and their sulfates.

Suppression of conditioned drinking by taurine and related compounds

Mice were conditioned to respond for water reinforcements on a FR-5 schedule. Taurine, injected intraperitoneally at doses of 9.0, 13.8, and 21.3 mmole/kg 30 min prior to the experimental session, produced a dose-related decrease in both the initial response rate and total number of reinforcements received by mice deprived of water for 24 hr. The structural analogues of taurine (aminomethanesulfonic acid, 3-aminopropanesulfonic acid, beta-alanine, cysteamine, and glycine) also produced a hypodipsia. Doses of taurine which produced depression of responding for water reinforcements were used which produced no suppression of spontaneous motor activity, rotarod performance, Sidman avoidance, or shuttle-box avoidance. After intraperitoneal injection, the concentration of taurine increased in the hypothalamus and medulla, but not in other brain areas. We suggest that taurine might be acting by specifically depressing areas of the hypothalamus which stimulate drinking.

Plasma disappearance of radioactivity after intravenous injection of labeled bile acids in man

The kinetics of disappearance of radioactivity from plasma after intravenous injection of radiolabeled bile acids was characterized in healthy subjects. Cholic and chenodeoxycholic acids and their N-glycine and N-taurine conjugates were studied along with the secondary bile acid, deoxycholic acid, and a synthetic conjugated bile acid, dehydrocholyltaurine. Disappearance of each primary bile acid was rapid and could be described by a biexponential curve (t 1/2 the first component, 1.7 to 3 min; second component, 7 to 16 min). Cholyglycine and cholyltaurine had identical disappearance rates which were significantly faster than the disappearance rates of chenodeoxycholylglycine and chenodeoxycholyltaurine, which were also identical. Radioactivity of a conjugated bile acid disappeared more rapidly than that of its unconjugated form, but all of these differences, although consistent, were small. Deoxycholic acid radioactivity disappeared slightly more slowly than that of the primary bile acids. In vitro, dihydroxy bile acids were bound by serum proteins more completely (96 to 98%) than trihydroxy bile acids (83 to 91%), whether free or conjugated, and binding was unrelated to bile acid concentration. Thus, plasma disappearance rates were related to the degree of protein binding to some degree in that those bile acids which were more tightly bound had the longer t 1/2 values. However, dehydrocholyltaurine showed little protein binding (42%), yet had the slowest disappearance rates; t 1/2 values averaged 4 and 36 min for the two components of the disappearance curve. The results suggest that the residence time of any bile acid in blood is extremely short, and that measurable concentrations of serum bile acids persist only because of continuous intestinal absorption. It is speculated that the reported difference between the pattern of fasting state serum bile acids and biliary bile acids is explained by differences in intestinal absorption and hepatic uptake of individual bile acids.