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R H Cagan

Publications and source records attributed to R H Cagan.

17 recordsLinked to original sources
PubMed1991

Sequential order of skin responses to surfactants during a soap chamber test.

Differences in the response of distinct layers of the skin to surfactants were probed using a modification of the Frosch and Kligman soap chamber test. Soap and other surfactant-containing cleansers were applied to the skin for 2 consecutive days. Transepidermal water loss showed that the stratum corneum is readily damaged even by a mild insult when no erythema is induced. A more severe treatment, such as 24-h exposure to a 5% soap solution, induced the maximal level of barrier damage but a submaximal level of erythema. Even 2 days of exposure to 5% soap does not elicit a maximal erythema response. These results suggest that the stratum corneum is more readily damaged than the dermis, which is not unexpected because the stratum corneum is the initial point of contact between surfactant and skin. Furthermore, this study indicates that for discriminating among mild products, when a small degree of irritation is induced, the most effective measure is stratum corneum damage assessed by evaporimetry. However, for evaluating more irritating products, erythema is probably the more discriminating evaluation technique.

Dermatitis, Contact↗
PubMed1990

Stratum corneum lipid removal by surfactants: relation to in vivo irritation.

The relationship between the in vivo irritation potential of sodium lauryl sulfate (SLS) and linear alkyl benzene sulfonate (LAS) and the ability of these two surfactants to remove lipid from the stratum corneum (SC) in vitro were investigated. Either surfactant removes detectable levels of lipids only above its critical micelle concentration (CMC). At high concentrations the surfactants removed only very small amounts of cholesterol, free fatty acid, the esters of those materials, and possibly squalene. SLS and LAS have been shown, below the CMC, to bind to and irritate the SC. Thus, clinical irritation provoked by SLS or LAS is unlikely to be directly linked with extraction of SC lipid. The milder forms of irritation--dryness, tightness, roughness--may involve both surfactant binding to and denaturation of keratin as well as disruption of lipid. Our findings challenge earlier assumptions that surfactants' degreasing of the SC is involved in the induction of erythema.

Alkanesulfonates↗
PubMed1979

Distribution of taste buds on fungiform and circumvallate papillae of bovine tongue.

The distribution of taste buds on the fungiform and circumvallate papillae of the cow tongue has been determined. The two tongues studied were from Holstein-Friesian cows four to six years of age; they contained 14,765 and 21,691 taste buds, respectively. The tip of the tongue is well supplied with fungiform papillae, and the posterior portion contains the circumvallate papillae. The midportion of the tongue contains relatively few taste papillae. The fungiform papillae contained 1,580 and 1,838 taste buds on the two tongues, respectively, and the circumvallate papillae were estimated to contain 13,185 and 19,853 taste buds. The highest concentration of taste buds therefore occurs in the circumvallate papillae; these relatively few papillae contain approximately 90% of the taste buds. On a circumvallate papilla, taste buds are found only on the papillary sidewall, with none either on the apical surface of the papilla or on the outer wall of the moat.

Animals↗
PubMed1979

Biochemical studies of taste sensation. VII. Enhancement of taste stimulus binding to a catfish taste receptor preparation by prior exposure to the stimulus.

The taste receptor membrane fraction (Fraction P2) was prepared from a homogenate of the taste tissue of the channel catfish Ictalurus punctatus. This included the rostral, dorsal, and dorsolateral surfaces of the catfish in addition to those of the barbels. The yield of Fraction P2 is 4-7 mg protein from an individual fish, with a purification averaging 8- to 15-fold over that of the crude whole homogenate and essentially quantitative recovery of binding activity in Fraction P2. Treatment of Fraction P2 in vitro with a high concentration of the taste stimulus molecule L-alanine led to a several-fold enhancement of binding activity. Enhancement of the binding of 3H L-alanine was observed after treatment with unlabeled 10 mM L-alanine and removal of the L-alanine by washing. Enhancement occurred whether the preparation was stored frozen (-65 degrees C) for an extended period in the presence of the L-alanine, or merely exposed to it in the cold without freezing. D-Alanine enhanced the binding activity of 3H L-alanine to about 60% of the level induced by L-alanine. Nonspecific binding of 3H L-alanine was unaffected by the treatment. Scatchard analyses of saturation curves for binding of 3H L-alanine to freshly prepared Fraction P2 and to L-alanine-treated Fraction P2 revealed no change in the KD value, but a several-fold increase occurred in the amount bound. Binding activity is operationally defined. Because the enhancement observed here is reminiscent of an increase in transport due to a countertransport effect, further studies were carried out to examine whether the phenomenon reflects transport or true binding. The measured binding was not increased in the presence of Na+, indicating that it is not due to an Na+-coupled transport of L-alanine. When Fraction P2 was preloaded with L-alanine (10(-6)--10(-2) M) prior to assay, no stimulation of binding was observed; instead, binding decreased. This result is consistent with a true binding phenomenon but not with a carrier-mediated transport process to explain the enhancement phenomenon. Binding assays carried out over a range of osmolarities revealed decreased binding at high osmotic strengths, suggesting that a significant portion of the ligand might be contained in vesicles. It is postulated that "hidden" or "buried" receptor sites exist in the Fraction P2 as isolated, and that these are exposed upon perturbation of the membrane structure by a high ligand concentration.

Alanine↗
PubMed1979

Biochemical studies of taste sensation--VIII. Partial characterization of alanine-binding taste receptor sites of catfish Ictalurus punctatus using mercurials, sulfhydryl reagents, trypsin and phospholipase C.

1. Taste receptors for L-alanine in the channel catfish Ictalurus punctatus have been partially characterized. The binding activity, which is localized to a sedimentable fraction (Fraction P2), was assayed with L-[3H]alanine as the ligand. 2. Addition of HgCl2 or p-mercuribenzoate to the assay at 0.1-1 mM markedly inhibited binding. The effect was not reversible and was unaffected by increased L-alanine in the binding assay. 3. The sulfhydryl reagents iodoacetate, 5,5'-dithiobis(2-nitrobenzoic acid), arsenite, and N-ethylmaleimide did not show appreciable inhibition of binding. The results suggest that the inhibitory effect of mercurials is not on specific sulfhydryl groups at alanine-binding sites. 4. Treatment of Fraction P2 with phospholipase C decreased binding activity and treatment with trypsin led to increased binding activity.

Alanine↗
PubMed1979

Biochemical studies of taste sensation: binding to taste tissue of 3H-labeled monellin, a sweet-tasting protein.

Binding of 3H-labeled methylated monellin to taste receptor tissue was demonstrated in vitro. Preparation of bovine and human circumvallate (taste) papillae bound more of the ligand than did lingual and nonlingual epithelial preparations devoid of taste buds. Binding to the taste preparations saturated at high ligand concentrations. Furthermore, sugars and other sweet-tasting molecules appeared to compete to some extent with this sweet-tasting protein for its binding sites. These binding measurements of the intensity sweet-tasting protein monellin to taste receptor preparations help to establish the binding interactions as an initial step taste sensation.

Animals↗
PubMed1978

Biochemical studies of olfaction: binding specificity of radioactively labeled stimuli to an isolated olfactory preparation from rainbow trout (Salmo gairdneri).

The extent of binding of 10 radioactively labeled odorant amino acids to a sedimentable fraction (fraction P2) derived from the olfactory rosettes of the rainbow trout Salmo gairdneri corresponded closely with their reported relative stimulatory effectiveness measured electrophysiologically. L isomers were bound to a greater extent than their respective D isomers. Binding of L-alanine was strongly and irreversibly inhibited by mercurials but was not affected by sulfhydryl-blocking reagents. Binding was saturable and reversible. Scatchard analyses gave evidence of two types of binding sites for most of the amino acids studied. The Kd values of the higher-affinity binding sites were similar among the amino acids, being in the range of 10(-6) M; differences occurred in the relative numbers of sites, n. These results, coupled with those from competition experiments, lead to the postulate that a multiplicity of types of olfactory binding sites exist in the trout: site TSA, which binds L-threonine, L-serine, and L-alanine; site L, which binds L-lysine; and site AB which binds beta-alanine. Tentative assignments are: site V, which binds L-valine; site H, which binds L-histidine; and site AD, which binds D-alanine. Site AD may be a lower affinity site for L-alanine. Binding of olfactory stimulus molecules appears to be an initial discrimination step in olfaction.

Amino Acids↗
PubMed1976

Biochemical studies of tast sensation. Binding of L-[3H]alanine to a sedimentable fraction from catfish barbel epithelium.

Large numbers of taste buds are distributed over the body surface of the channel catfish ictalurus punctatus, with the barbels having an especially high density. L-Alanine, as well as certain other amino acids, are taste stimuli in this animal. Epithelial tissue obtained by gentle scraping of the barbel surface was fractionated by differential centrifugation. A sedimentable fraction (P2) was prepared that was enriched in L[OH]alanine binding activity, the plasma membrane marker enzyme 5'-nucleotidase, and the mitochondrial marker succinate cytochrome c reductase, but not the microsomal marker NADH cytochrome c redu.ctase. Binding of L-[OH]alanine was measured using a Millipore filter method in which correction for non-specific binding was also determined. Time, temperature, and pH for measuring binding activity were established. At the optimal pH of 7.8, the KD for L-alanine is 4.8 X 10(-6) M. The first order dissociation rate constant at 6 degrees is 3.8 X 10(-4) s-1 and at 24 degrees it is 12.1 X 10(-4) s-1. The second order rate constant for association is between 10(2) and 10(3) M-1 S-1. Reversibility of the binding interaction was also demonstrates by the rapid displacement of bound L-[3H]alanine by a large excess of unlabeled L-alanine. That the binding does not represent incorporation into protein was confirmed by the lack of effect of puromycin. The amounts bound of several other chemostimulatory amino acids werealso determined.

Alanine↗
PubMed1976

Biochemical studies of taste sensation: II. Labelling of cyclic AMP of bovine taste papillae in response to sweet and bitter stimuli.

Labeling of cyclic AMP of tase papillae and its responsiveness to tast stimuli has been measured using whole papillae from bovine tongue prelabeled with [ 8-(14) C] adenine. Labeling was measured in circumvallate and fungiform papillae, both of which contain taste buds, and in filiform papillae and small blocks of tongue epithelium, which are devoid of taste buds. No differences were observed in the levels of activity. The labeling of cyclic AMP of circumvallate papillae showed only small increases (12-22%) in the presence of the taste stimulus sucrose (sweet), and the stimulatory effects were not statistically significant. The increase due to sucrose was not potentiated by theophylline. No stimulation by sucrose was observed with epithelium controls. Lactose, which is a poor taste stimulus, did not stimulate labeling of cyclic AMP in taste papillae. Theophylline, caffeine, and quinine (bitter) stimulated labeling of cyclic AMP by up to 2-fold, as did L-Epinephrine. Evidence for a specific role of cyclic AMP as a second messenger in taste sensation was not obtained. It is suggested that cyclic AMP might provide a mechanistic basis for studying some of the effects of sweet and bitter compounds in mixtures.

Adenine↗
PubMed1976

Biochemical studies of taste sensation. III. Preparation of a suspension of bovine taste bud cells and their labeling with a fluorescent probe.

A method to prepare suspensions of taste bud cells is described. Bovine circumvallate papillae, which contain most of the taste buds in this animal, are incubated in collagenase-containing medium and the epidermal sidewall tissue is then dissected from the inner gelatinous dermis. The sidewall tissue, which contains the taste buds, is gently homogenized by manual operation of an all-glass homogenizer with a loose-fitting pestle. The suspended material is separated on a discontinous Ficoll gradient (2%, 8%, 10%, 12% w/w). The material banding at the 8-2% interface is greatly enriched in spindle-shaped cells that are morphologically similar to taste bud cells as they appear in situ. These cells are not seen when the procedure is done with tissues devoid of taste buds, namely the upper surface of the circumvallate papilla or epithelium from the intermolar eminence. Fluorescence analysis indicates that the hydrophobic probe, 8-anilino-1-naphthalenesulfonate (ANS), binds to relatively nonpolar sites in the suspension. It is postulated that the probe is adsorbing onto the surface membrane of the cell. These preparations may be useful in studying specificity and transduction in taste sensation.

Anilino Naphthalenesulfonates↗
PubMed1976

The sulfhydryl group of monellin: its chemical reactivity and importance to the sweet taste.

The presence of a single cysteine in the sweet-tasting protein monellin was confirmed by titrations with p-hydroxymercuribenzoate (PHMB) and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). The sulfhydryl group in native monellin reacts very slowly with each of these reagents, indicating that the sulfhydryl is relatively inaccessible. In the presence of either 6 M guanidine-HCl, 8 M urea, or 1% sodium dodecyl sulfate, the rate of reaction of the sulfhydryl group with titrant is dramatically increased. Under a variety of conditions, the presence of 1 mole of sulfhydryl per mole of protein (of molecular weight 10,700) was found. Reaction of the sulfhydryl by titration with PHMB or DTNB leads to loss of sweetness. The free sulfhydryl is also lost by carboxymethylation of monellin in the presence of guanidine-HCl, yielding a protein that is not sweet. Exposure to air in the presence of denaturant leads to a decrease in the sweetness of monellin. Sweetness of the PHMB-reacted monellin can be recovered upon treatment of the protein with mercaptoethanol, and the partial loss of sweetness that occurs with air exposure is lessened in the presence of mercaptoethanol. It is postulated that alteration of the single sulfhydryl group of monellin leads to a change in the tertiary structure of the protein and hence its sweet taste.

Chemical Phenomena↗
PubMed1975

Effects of denaturants on the sweet-tasting protein monellin.

Effects of the denaturants urea and guanidine-HCl on the sweet-tasting protein monellin have been studied. The pH at which monellin is initially treated with denaturant is an important factor in retention of sweetness, but the pH maintained during subsequent removal of denaturant by dialysis has no effect on activity. Recovery of sweetness of denaturant-treated monellin is favored when denaturation occurs at acid pH. Monellin treated with either 6 M guanidine-HCl or 8 M urea at acid pH retains all of its sweetness following removal of denaturant, but urea treatment at neutral pH leads to some irreversible loss of sweetness. Monellin precipitates from solution under some conditions during removal of denaturant by dialysis, and the precipitated protein is no longer sweet. Precipitation is least under acid conditions. Aggregated protein was demonstrated by gel filtration chromatography. The single sulfhydryl group of monellin was not demonstrable in the precipitated protein, having apparently become oxidized during denaturation and formation of the aggregated protein. The data support the hypothesis that the tertiary structure is important in the ability of monellin to elicit a sweet sensation.

Guanidines↗