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S N Murthy

Publications and source records attributed to S N Murthy.

72 records · Page 4Linked to original sources
PubMed1981

The aldolase-binding site of the human erythrocyte membrane is at the NH2 terminus of band 3.

Band 3 is the predominant membrane-spanning polypeptide and the mediator of anion transport in the human erythrocyte. In addition, it provides the sites of association for fructose 1,6-bisphosphate aldolase and other cytoplasmic proteins with the membrane. The aldolase-binding activity of water-soluble fragments of band 3 was measured by their inhibition of aldolase catalytic activity and by their displacement of aldolase from ghosts. At saturation, the binding of one band 3 or certain of its fragments per aldolase molecule partially inhibited the catalytic activity and band 3 binding of the unliganded subunits of the tetramer through an apparently cooperative mechanism. An NH2-terminal 23,000-dalton fragment generated by S-cyanylation of the cytoplasmic pole of band 3 was approximately 20% as avid in binding aldolase as was native band 3. Several fragments cleaved from the NH2-terminal portion of the 23,000-dalton peptide by trypsin, mild acid hydrolysis, and cyanogen bromide digestion all bound aldolase, while fragments from the rest of the polypeptide were essentially inactive. The first 31 residues of band 3 contained 16 Asp plus Glu, no basic residues, and a blocked alpha-amino terminus. The highly acidic composition of this region is consistent with the strongly electrostatic character of the interaction between band 3 and aldolase, presumably at the strongly basic catalytic center of the enzyme. We conclude that the NH2-terminal region of band 3 bears the membrane-binding site for aldolase.

Amino Acids↗
PubMed1980

Effect of pH, substrate, and temperature on tryptic activity of duodenal samples.

Many tests of pancreatic exocrine function are based on the estimation of tryptic activity in duodenal juice. However, tryptic activity may be influenced by substrate, pH, and temperature. We studied the effect of substrate, pH, and temperature on tryptic activity of duodenal juice in vitro and in vivo. TAME yielded higher tryptic activity in vitro (11.25 times) and in vivo (4.54 times) compared to BAEE and BAME. Our in vitro studies also indicated that trypsin was denatured slowly between pH 6 and 4.25 and rapidly between 4.25 and 3.75. The rate of denaturation was faster at room temperature and slower in ice over a broad range of pHs. In our in vivo studies, hypersecretors showed tryptic activities consistently lower than normosecretors. The duodenal pHs of the hypersecretors were consistently lower than those of normosecretors, suggesting that the low tryptic activities were secondary to denaturation by acid. These studies indicate that the activity of trypsin in duodenal juice varies significantly with substrate, pH, and temperature. These factors must, therefore, be considered in the analysis and interpretation of trypsin.

Duodenum↗
PubMed1978

Serial pH changes in the duodenal bulb during smoking.

The effect of smoking on the pH of the duodenal bulb was studied in 10 normosecretors and 10 hypersecretors using a Beckman pH electrode. The pH was monitored during three study periods, basal, smoking, and postsmoking, of 1 hr each. The pH remained below 3.5 significantly longer during the smoking period compared to the basal period for both groups. The bulbar pH remained under 3.5 during the smoking period longer in the hypersecretor group compared to the normosecretor group (60 versus 20%). Hypersecretors who were smokers exhibited acidic bulbar pH values longer and more consistently than hypersecretor-nonsmokers during smoking. In 5 hypersecretors with data for both bulbar pH and bicarbonate output, inhibition of bicarbonate output during smoking was generally associated with acidic pH values in the bulb. These observations suggest that the association between cigarette smoking and peptic ulcer disease may be attributable to, in part, the persistently acidic pH values in the duodenal bulb during smoking. This study further suggests that the degree and the duration of acidification of the duodenal bulb during smoking are influenced by the secretory and the smoking status of the subject.

Adult↗
PubMed1977

Simultaneous measurement of basal pancreatic, gastric acid secretion, plasma gastrin, and secretin during smoking.

The effect of smoking one unfiltered cigarette every 15 min for 1 hr on basal gastric acid and pancreatic secretion was studied in 10 subjects with a history of duodenal ulcer and 10 without duodenal ulcer. Smoking induced a transient rise of basal acid output followed by a slight decrease. This effect was more pronounced in the duodenal ulcer group. Smoking markedly inhibited fluid and bicarbonate secretion during the smoking period. The bicarbonate and fluid secretion returned to control levels within 30 to 60 min in the ulcer group and in 60 to 90 min in the nonulcer group. There was no difference in the degree of inhibition of pancreatic secretion between the two groups. Immunoreactive gastrin and secretin in the peripheral venous blood did not change significantly during smoking. The degree of inhibition of basal pancreatic secretion correlated well with the plasma concentrations of nicotine. These observations indicate that smoking in the fasting state induces alterations of basal gastric and pancreatic secretions which are not related to changes in plasma gastrin and secretin concentration, but to plasma concentrations of nicotine. The implication of this study in relation to a possible causal association between cigarette smoking and peptic ulcer disease is discussed.

Adult↗
PubMedDate not supplied

Effect of binge cocaine treatment on hindlimb vascular function.

Chronic cocaine abuse is known to cause endothelial dysfunction and atherosclerosis. The present study investigated the effect of binge cocaine treatment, a model for chronic cocaine abuse, on the blood flow responses to the adrenergic agonists norepinephrine, phenylephrine and isoproterenol, the endothelium-dependent vasodilator acetylcholine, and the endothelium independent vasodilator sodium nitroprusside (SNP) in the hindlimb vascular bed of male Sprague Dawley rats. Rats received either single binge or double binge treatment. Each binge treatment consisted of three doses of cocaine (30 mg kg(-1) i.p.) for 3 days. For double binge treatment, there was a 4 day recovery period between the binges. At the end of the treatment the rats were anesthetized and agonists were administered into the right hindlimb circulation through a catheter in the left iliac artery and blood flow responses were measured with a flow probe around the right iliac artery. Rats receiving double cocaine binges showed a significant decrease in the magnitude and duration of the blood flow response to norepinephrine and a decrease in the duration of the blood flow response to phenylephrine, isoproterenol and acetylcholine when compared with saline controls. The blood flow response to SNP was not changed. Total plasma nitrate-nitrite levels were significantly reduced and big endothelin levels were significantly increased in rats receiving double cocaine binges. This study demonstrates that binge cocaine treatment can alter endothelial function, while not changing smooth muscle function, and impairs the adrenergic pathway.

Acetylcholine↗
PubMedDate not supplied

The effect of cyclic nucleotides on secretin secretion in canine duodenal mucosa in vitro.

We examined the effects of cyclic nucleotides and calcium on secretin release from canine duodenal mucosal explants incubated in organ culture media. Time course studies revealed that at pH 7.4, 5 and 10 mM dibutyryl cyclic adenosine monophosphate (DBcAMP) increased secretin release progressively, reaching a peak at 2 hours. Two mM of DBcAMP at pH 7.4 did not increase secretin release but at pH 4.5, all 3 doses potentiated secretin release. DBcAMP-stimulated secretin release was not dependent on the influx of extracellular calcium. Graded doses of 3-isobutyl-1-methylxanthine (IBMX) did not stimulate secretin secretion but 1 mM IBMX with 2 mM DBcAMP increased secretin secretion significantly. Dibutyryl cyclic guanosine monophosphate, cholera toxin and 5'-guanylyl-imidodiphosphate (GPP(NH)p) did not stimulate basal secretion release. The release of secretin from our explants incubated at pH 7.4 was not due to specific leakage because all of our viability studies revealed that our explants were functionally intact at the end of 2 hours. Our observations suggest that cyclic nucleotides may participate in the intracellular regulation of secretin secretion.

1-Methyl-3-isobutylxanthine↗
PubMedDate not supplied

Effect of the secretin family of peptides on gastric emptying and small intestinal transit in rats.

We have compared the effects of the secretin family of peptides and their synthetic fragments on gastric emptying (GE) and small intestinal transit (SIT) using an unanesthetized rat model which simultaneously measures the GE and SIT of both solids and liquids. The meal consisting of 5% polyethylene glycol w/v, 5% Indian ink v/v and 20 non-digestible plastic beads was given intragastrically 10 minutes after the intraperitoneal injection of 0.5 ml of saline or peptides (2 and 5 micrograms/kg). Plasma secretin and the immunospecificity of secretin fragments were determined. In control rats, the t1/2 for the GE of both solids and liquids were 56 +/- 3.8 and 19 +/- 2.3 minutes, respectively. Liquids emptied faster than the solids and liquids travelled ahead of the solids in the intestine. Secretin (5 micrograms/kg) inhibited GE of both solids and liquids by 33-37%. Secretin delayed the SIT of the meal by approximately 35%. Fragments of secretin and of VIP had no effect on GE and SIT of both solids and liquids. The whole molecule of secretin was required to inhibit GE and to delay SIT of solids and liquids. Glucagon, PHI and growth hormone releasing factor (GHRF1-44) inhibited GE and SIT of both solids and liquids. For all peptides tested, the inhibition of SIT was proportional to the inhibition of GE suggesting that the prolongation of SIT was secondary to delayed GE. These observations indicate that the peptides of the secretin family inhibit GE and prolong SIT. Thus, the structural requirement required for the secretin family of peptides to effect their motor actions on the stomach is similar to that required for pancreatic enzyme secretion.

Animals↗
PubMedDate not supplied

Possible involvement of protein kinase C in mediating gastrin-induced response in rat colonic epithelium.

We examined the potential role of protein kinase C in signal transduction induced by gastrin's stimulation of rat colonic epithelium. Protein synthesis ([35S]methionine incorporation into protein) and enzyme activity (decrease in the cytosolic activity) were measured following epithelial stimulation with gastrin. Gastrin (10 nM) increased [35S]methionine incorporation into protein to 265% above maintenance level. The effect of gastrin was comparable to the stimulation induced by phorbol 12-myristate, 13-acetate (PMA), a strong activator of protein kinase C. The increase in protein synthesis induced by gastrin was totally abolished by 1-(5-isoquinolinyl)-2-methylpiperazine, an inhibitor of protein kinase C activity. Gastrin also decreased the cytosolic activity of the enzyme, an index of its activation and subsequent translocation to other cellular compartments. Therefore, we conclude that gastrin may be acting through a protein kinase C mechanism.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMedDate not supplied

Gastrin induction of mRNA expression in rat colonic epithelium in vitro.

A newly developed system of isolated rat colonic epithelial cells was utilized for a comprehensive study of protein synthesis influenced by gastrin. We found that synthetic human gastrin (0.01-100 nM) increased the incorporation of [35S]methionine into proteins within 2 hours. Peak incorporation was observed with 10 nM gastrin to more than two-fold above maintenance levels. Actinomycin-D (10 micrograms/ml) inhibited the stimulated increases in total protein synthesis indicating that the peptide's trophic effect was mediated by the synthesis of new mRNA species. The effect of gastrin was comparably stronger than the one induced by the mitogen bombesin (1 nM). However, bombesin, a neuromodulator of gastrin release, did not produce an additive effect beyond that of gastrin on total protein synthesis. Gastrin stimulated the synthesis of many polypeptides resolved on two-dimensional polyacrylamide gel, an indicator of gastrin's influence on the expression of various mRNA species. Some of these polypeptides may be used as markers in investigating colonic epithelial response to gastrin.

Animals↗
PubMedDate not supplied

Acute effect of substance P in immunologic vasculitis in the rat colon.

Substance P has been implicated as a neuronal mediator of inflammation in various inflammatory conditions. However, the exact role played by substance P in inflammatory bowel diseases or in experimental colonic vasculitis has not been clearly understood. In this study, we examined the effect of close superior mesenteric artery injection of substance P under prevailing inflammatory conditions induced by intravenous human albumin antialbumin immune complex followed by intracolonic perfusion of 2.5% formaldehyde in rats or intracolonic perfusion of 5% alcohol alone. The immune complex- and formaldehyde-treated rats showed severe microvascular changes such as microvascular plugging by red blood cells, endothelial breakage and extravasation of plasma proteins and red blood cells. The bolus injection of 10(-8) M substance P reduced extravasation of Evans blue dye by 50% and the tissue wet to dry ratio by 20% in immune complex- and formaldehyde-perfused rats. Myeloperoxidase activity was not changed. Substance P also significantly inhibited (44%) the extravasation in alcohol-perfused rats. Pretreatment of immune complex- and formaldehyde-treated rats with substance P antagonist reversed the effect of substance P. These findings suggest that the most immediate effect of substance P may be vasodilation and clearing of vascular plugs induced by immune complex and formaldehyde. This effect of substance P differs from its chronic effect, which causes vasodilation and extravasation.

Acute Disease↗
PubMedDate not supplied

Biotinylated peptides containing a factor XIIIa or a tissue transglutaminase-reactive glutaminyl residue that block protein cross-linking phenomena by becoming incorporated into amine donor sites.

Biotinylated peptides Biot-Gln-Gln-Ile-Val and Biot-epsilon-Aca-Gln-Gln-Ile-Val were shown to act as acceptor substrates for amines in reactions catalyzed by both tissue transglutaminase and coagulation factor XIIIa. Moreover, the peptides could be employed for specifically blocking the potential amine donor sites of protein substrates participating in biological cross-linking with these enzymes. The presence of the biotin label allowed for ready detectability of the marked donor substrates during the cross-linking of crystallins in lens homogenate by the intrinsic transglutaminase and that of the alpha chains of human fibrin by factor XIIIa.

Amines↗
PubMedDate not supplied

Influence of cations on activated-sludge effluent quality.

Laboratory experiments and field tests were conducted to determine the effect of inorganic cations on effluent from activated-sludge systems. Laboratory experiments showed that monovalent cations tend to increase the concentration of solution biological polymers (biopolymers), whereas divalent cations tend to retain the biopolymers in the floc. Biopolymers in solution affect effluent chemical oxygen demand (COD). Coagulation tests were performed on the effluent with ferric chloride. Ferric hydroxide can coagulate protein through possible adsorptive interactions and may be responsible for some biopolymer retention in the flocs. In the field study, it was found that sodium ions in the influent wastewater caused an increase in proteins and polysaccharides in solution, thereby increasing the effluent COD concentration of the treated municipal wastewater. The attachment or release of these microbially derived organic biopolymers and recalcitrant influent substrate may depend on the monovalent-to-divalent cation ratio and the concentration of iron. Modeling of effluent organics in the activated-sludge process can be enhanced through incorporation of concepts that take into account the partitioning (between floc and solution) of microbial biopolymers and influent recalcitrant substrate.

Biopolymers↗