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S G Schultz

Publications and source records attributed to S G Schultz.

At least 109 records · Page 6Linked to original sources
PubMed1971

Studies on the electrical potential profile across rabbit ileum. Effects of sugars and amino acids on transmural and transmucosal electrical potential differences.

When isolated strips of mucosal rabbit ileum are bathed by physiological electrolyte solution the electrical potential difference (PD) across the brush border (psi(mc)) averages 36 mv, cell interior negative. Rapid replacement of Na in the mucosal solution with less permeant cations, Tris or choline, results in an immediate hyperpolarization of psi(mc). Conversely, replacement of choline in the mucosal solution with Na results in an abrupt depolarization of psi(mc). These findings indicate that Na contributes to the conductance across the brush border. The presence of actively transported sugars or amino acids in the mucosal solution brings about a marked depolarization of psi(mc) and a smaller increase in the transmural PD (Deltapsi(ms)). It appears that the Na influx that is coupled to the influxes of amino acids and sugars is electrogenic and responsible for the depolarization of psi(mc). Under control conditions Deltapsi(ms) can be attributed to the depolarization of psi(mc) together with the presence of a low resistance transepithelial shunt, possibly the lateral intercellular spaces. However, quantitatively similar effects of amino acids on psi(mc) are also seen in tissues poisoned with metabolic inhibitors or ouabain. Under these conditions Deltapsi(mc) is much smaller than under control conditions. Thus, the depolarization of psi(mc) might not account for the entire Deltapsi(ms), observed in nonpoisoned tissue. An additional electromotive force which is directly coupled to metabolic processes might contribute to the normal Deltapsi(ms).

Alanine↗
PubMed1970

Effects of monovalent cations on the sodium-alanine interaction in rabbit ileum. Implication of anionic groups in sodium binding.

H, K, Rb, and Li inhibit Na-dependent alanine influx across the brush border of rabbit ileum. Kinetic analysis indicates that H and K behave as competitive inhibitors of influx so that increasing the concentration of H or K in the mucosal solution is kinetically indistinguishable from decreasing the Na concentration. In addition the coupling between alanine and Na influxes is markedly reduced at pH 2.5. With the exception of H and Li, none of these monovalent cations significantly affects carrier-mediated alanine influx in the absence of Na indicating that their inhibitory effects are largely restricted to the Na-dependent fraction of influx. Increasing H concentration from 0.03 to 3 mM does not affect influx in the absence of Na but markedly inhibits influx in the presence of Na. Li significantly enhances alanine influx in the absence of Na. Ag, UO(2), and La also inhibit the Na-dependent fraction of alanine influx. These findings suggest that anionic groups having a pK(a) of approximately 4 are involved in the interaction between Na and the alanine-carrier complex; present evidence implicates carboxylate groups however, phosphoryl residues cannot be ruled out. The previously proposed kinetic model for the Na-alanine interaction has been extended to accommodate these effects of H and other monovalent cations. The mechanistic and physiological implications of these findings are discussed.

Alanine↗
PubMed1970

Dicarboxylic amino acid influx across brush border of rabbit ileum. Effects of amino acid charge on the sodium-amino acid interaction.

Glutamate and aspartate influxes across the brush border of rabbit intestine are saturable processes that are subject to competitive inhibition and are markedly influenced by the Na concentration in the mucosal solution. Lowering the Na concentration increases the amino acid concentration needed to elicit a half-maximal influx but does not significantly affect the maximal influx. The interaction between Na and anionic amino acid influx can be described by the same kinetic model that has been applied to the influxes of neutral amino acids and lysine. Comparison of the kinetic parameters for anionic, neutral, and cationic amino acids suggests that amino acid charge influences (a) the stability of the binary (amino acid-site) complex and (b) the affinity of this binary complex for the subsequent binding of Na. A mechanistic interpretation of these interactions is proposed.

Animals↗
PubMed1969

Lysine transport across isolated rabbit ileum.

Lysine transport by in vitro distal rabbit ileum has been investigated by determining (a) transmural fluxes across short-circuited segments of the tissue; (b) accumulation by mucosal strips; and (c) influx from the mucosal solution across the brush border into the epithelium. Net transmural flux of lysine is considerably smaller than that of alanine. However, lysine influx across the brush border and lysine accumulation by mucosal strips are quantitatively comparable to alanine influx and accumulation. Evidence is presented that the "low transport capacity" of rabbit ileum for lysine is due to: (a) a carrier-mediated process responsible for efflux of lysine out of the cell across the serosal and/or lateral membranes that is characterized by a low maximal velocity; and (b) a high "backflux" of lysine out of the cell across the mucosal membrane. A possible explanation for the latter observation is discussed with reference to the relatively low Na dependence of lysine transport across the intestinal brush border.

Alanine↗
PubMed1969

Sodium and sugar fluxes across the mucosal border of rabbit ileum.

Unidirectional influxes of sugars and Na from muscosal solution into the cells of rabbit ileum have been examined. The influxes of glucose, galactose, and 3-0-methyl glucose (3 MG) follow Michaelis-Menten type kinetics and are markedly dependent on the presence ofNa in the mucosal solution. For 3 MG, reduction of Na concentration causes a decrease in maximal rate of influx and little change in the "apparent Michaelis constant." There appeared to be little mediated entry of 3 MG into the cells from Na-free solution. The influx of Na was increased by the presence of 3 MG in the mucosal solution and at all Na concentrations tested, there was a 1:1 ratio between sugar influx and the sugar-dependent Na influx. On the basis of these observations, a model has been developed for the sugar transport system involving a transport site that combines with both sugar and Na.

Animals↗