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H Sankaran

Publications and source records attributed to H Sankaran.

At least 37 records · Page 2Linked to original sources
PubMed1985

Reversible acetaldehyde inhibition of A23187-stimulated amylase secretion from isolated rat pancreatic acini.

The Ca2+ ionophore, A23187, stimulated amylase secretion from isolated rat pancreatic acini in a dose-dependent manner with a maximal effect at 6 microM. Acetaldehyde, a metabolite of ethanol, caused a reduction in the magnitude of ionophore-stimulated secretion with no evidence of competitive inhibition. Furthermore, 6 microM ionophore-stimulated amylase secretion was dose-dependently inhibited by acetaldehyde. This inhibitory effect of acetaldehyde, however, was reversible on washing and reincubating acetaldehyde-treated acini. These results suggest that acetaldehyde reversibly inhibits intracellular components mediating stimulated secretion and this inhibition requires a continuous chemical interaction between acetaldehyde and intracellular component(s) regulating stimulated enzyme secretion.

Acetaldehyde↗
PubMed1984

Effect of ethanol on cholecystokinin-induced enzyme secretion from isolated rat pancreatic acini.

Cholecystokinin octapeptide (CCK8)-stimulated amylase release in isolated rat pancreatic acini was inhibited over 30% by 600 mM ethanol. The configuration of the dose-response curve for CCK8, however, in the presence of ethanol was similar to that of the control. Amylase release elicited by maximal concentrations of CCK8 (300 pM) was inhibited by increasing concentrations of ethanol (0.3 to 1.3 M), and this inhibition was concentration dependent. In addition, the binding of [125I]CCK33 to specific membrane receptors on acini was inhibited by ethanol in a dose-dependent manner. A positive correlation between the inhibitory effects of ethanol on CCK binding and CCK-induced amylase release was observed. Furthermore, these inhibitory effects of ethanol were reversible. Basal amylase release, however, was increased 20-50% by ethanol between the concentrations of 0.3 and 1.3 M; higher concentrations caused a leakage of amylase from the acini both in the absence and presence of 300 pM CCK8. This is confirmed by 51Cr release from prelabeled acini which revealed no significant damage to acinar cell membrane between 0.3 and 1.6 M ethanol, but significant damage to acini at higher concentrations. These data suggest that the 600 mM ethanol-induced inhibition of CCK action in acini is due to reversible perturbation of the acinar cell membrane.

Amylases↗
PubMed1983

Action of the venom of the scorpion Tityus trinitatis on pancreatic insulin secretion.

In vivo, canine pancreas was stimulated to secrete insulin by the venom of the scorpion Tityus trinitatis; the venom also caused a rise in plasma glucose level as well. The venom-induced insulin secretion was also observed under in vitro conditions in rat pancreatic slices, and this stimulation was dose-related. Maximal effect was observed at 20 micrograms/ml. Atropine (3 x 10(-6) M) completely abolished both venom (20 micrograms/ml)- and acetylcholine (3 x 10(-7) M)-induced insulin secretion. It is suggested that the venom-induced insulin secretion is mediated through muscarinic cholinergic mechanisms.

Animals↗
PubMed1983

Biological activity of canine intestinal cholecystokinin-58.

The biological activity of a recently characterized cholecystokinin molecule, canine CCK-58, has been tested using perifused canine gallbladder strips and isolated mouse pancreatic acini. It has been shown that canine CCK-58, purified by affinity chromatography and molecular sieve chromatography, is biologically as potent as canine CCK-39,33 (component II) and synthetic CCK-8. The biological responses were inhibited by dibutyryl cGMP, a known CCK antagonist. CCK-58 is one of the main large molecular forms of CCK in the intestine mucosa. Whether CCK-58 is only an intracellular precursor of other CCK molecules or an important circulating hormone cannot be determined from the data currently available.

Acetylcholine↗
PubMed1982

Inhibitory effects of scorpion venom on the uptake of amino acids by synaptosomes and synaptosomal membrane vesicles.

Scorpion (Tityus serrulatus) venom strongly inhibited the Na+-dependent uptake of (( 14C ))proline by rat brain synaptosomal preparations. In addition, the efflux of proline was enhanced markedly by scorpion venom. The inhibitory effects of the venom were also demonstrated in synaptosomal vesicle preparations where proline uptake was energized by an artificially imposed Na+ gradient. In both preparations, the effect of scorpion venom was additive with the inhibitory effect of veratridine on Na+-dependent amino acid uptake. The inhibitory effects of both compounds were abolished by tetrodotoxin. The Na+-dependent uptakes of amino acids (e.g. proline, glutamic acid, and gamma-aminobutyric acid) were much more sensitive to inhibition by the toxin than the Na+-independent uptakes (e.g. leucine and phenylalanine). The results of the present study indicate that the scorpion venom may exert its inhibitory effect on Na+-dependent transport by decreasing the transmembrane Na+ gradient. Efflux of accumulated proline, which is presumably controlled by maintenance of this Na+ gradient, was stimulated 3- to 4-fold by the scorpion venom.

Amino Acids↗
PubMed1982

Relationship of cholecystokinin receptor binding to regulation of biological functions in pancreatic acini.

Cholecystokinin (CCK) was conjugated to 125I-Bolton-Hunter reagent (125I-BH-CCK), and the binding of this ligand to CCK receptors in isolated mouse pancreatic acini was correlated with the regulation by CCK of both amylase release and the transport of 2-deoxyglucose and alpha-aminoisobutyric acid. Stimulation of amylase release by CCK was biphasic. At low CCK concentrations (less than 200 pM), amylase release was progressively stimulated, whereas at higher CCK concentrations (greater than 200 pM), amylase release was progressively reduced. In contrast, stimulation of 2-[3H]deoxyglucose transport and inhibition of alpha-[3H]aminoisobutyric acid transport were monophasic, being one-half maximal at 0.85 and 0.44 nM, respectively. Under incubation conditions identical to those employed for measuring biological functions, the binding of 125I-BH-CCK to receptors in acini was rapid and reversible. Competition-inhibition curves and Scatchard plots of equilibrium binding were compatible with two orders of binding sites. Employing a computer program for analysis of multiple binding sites, a high-affinity, low-capacity binding component having a Kd of 26 pM and a lower-affinity, higher-capacity binding component having a component Kd of 2.2 nM were resolved. Regulation of 2-[3H]deoxyglucose and alpha-[3H]aminoisobutyric acid uptake appeared, therefore, to be the result of fractional occupancy of the lower-affinity CCK receptors. Regulation of amylase released was more complex and appeared to be due to the concomitant occupancy of both the high- and low-affinity CCK receptors.

Amylases↗
PubMed1982

Quantitative electron microscope autoradiographs of 125I-cholecystokinin in pancreatic acini.

To morphologically evaluate the interaction of cholecystokinin (CCK) with its receptors on pancreatic acinar cells, we incubated isolated mouse acini at 37 degrees C with radioiodinated CCK and then prepared quantitative electron microscope autoradiographs. Specific binding of CCK to acini was one-half maximal at 2 min of incubation and maximal after 10 min. The cell-associated radioactivity was extracted and analyzed on Sephadex G-50. After 2 min, 90% of the total cellular radioactivity remained as intact CCK; after 30 min, the intact radioactivity decreased to 65% of total. At 2 min, the fraction of bound hormone that fixed to acini was 84% of total; this amount decreased to 78% after 30 min. Thus, the majority of radioactivity in the autoradiographs at both time points was intact CCK; however, at 30 min, a small amount was also degraded hormone. After both 2 and 30 min of incubation, silver grains were highly concentrated over the basolateral plasma membrane. A significant number of grains were in the cell interior at both time points, increasing from 13% of total grains at 2 min to 42% at 30 min. At both times, the largest fraction of internalized grains was localized over the endoplasmic reticulum. At 30 min, a significant concentration of CCK grains was observed over multivesicular bodies. The present study demonstrates, therefore, that CCK binds to specific receptors on the basolateral surface of pancreatic acinar cells. After binding, the hormone is internalized, locates predominantly on the endoplasmic reticulum, and is then degraded.

Animals↗
PubMed1981

Insulin action in pancreatic acini from streptozotocin-treated rats. I. Stimulation of protein synthesis.

Pancreatic acini were prepared from rats rendered diabetic with streptozotocin. In this tissue, insulin stimulated [3H]leucine incorporation into protein. The full effects of insulin on this function were not immediate but increased linearly with time for up to 2 h of incubation. Insulin had a detectable effect on l eucine incorporation at 50 pM, a half-maximal effect at 0.7 nM, and a maximal effect at 30 nM. Desdipeptide proinsulin was only 10% as potent as native insulin in stimulating [3H]leucine incorporation, whereas proinsulin and desoctapeptide insulin were only 1% as potent. Insulin also increased the incorporation of [3H]valine and [35S]methionine into protein but did not increase the influx of either [14C]cycloleucine or alpha-[3H]aminoisobutyric acid. These observations suggested that the increased incorporation of labeled amino acid into protein reflected stimulation of protein synthesis rather than stimulation of amino acid transport. Furthermore, insulin at 1.67 nM significantly increased the acinar cell concentration of amylase. The present findings are consistent therefore with the concept that insulin regulates pancreatic exocrine functions, including protein and enzyme synthesis.

Amino Acids↗
PubMed1981

Insulin action in pancreatic acini from streptozotocin-treated rats. II. Binding of 125I-insulin to receptors.

The binding of 125I-insulin to its receptors was investigated with isolated pancreatic acini obtained from diabetic rats under incubation conditions identical to those used to study the effects of insulin on acinar cell protein synthesis. Binding was specific, time dependent, reversible, and linearly related to the acinar protein content. Degradation of insulin after 30 min of incubation was less than 10% of the total hormone present in the incubation medium. 125I-insulin dissociated from acini with a one-half time of 9 min. Unlabeled insulin at 83.5 nM accelerated the rate of dissociation of labeled insulin. 125I-insulin binding to acini was competitively inhibited by insulin and its analogues in proportion to their biological potencies. Scatchard analysis revealed a major class of insulin-binding sites with a Kd of 1.6 nM; maximal stimulation of protein synthesis was observed when > 90% of these high-affinity receptors were occupied. These studies indicate, therefore, that insulin binding to receptors on pancreatic acini can be correlated with subsequent regulation of biological functions.

Animals↗
PubMed1981

Mechanism of scorpion toxin-induced enzyme secretion in rat pancreas.

Scorpion venom induces acute pancreatitis in humans and stimulates pancreatic hypersecretion in several animal species. To clarify whether scorpion toxin influences pancreatic function directly by stimulating the acinar cells or influences pancreatic function indirectly by stimulating pancreatic nerves, we measured amylase release from both rat pancreas lobules (containing both acinar cells and nerves) and isolated rat pancreatic acini (acinar cells only). Scorpion toxin stimulated amylase release from lobules to a similar extent as did carbamylcholine, an acetylcholine agonist. In these lobules, the effect of scorpion toxin was blocked by both atropine (an inhibitor of the cholinergic receptor on acinar cells) and tetrodotoxin (a selective blocker of Na+ channels in nerves). In contrast, the effect of carbamylcholine was blocked by atropine, but not by tetrodotoxin. In isolated pancreatic acini, carbamylcholine was without effect. We conclude that scorpion toxin influences pancreatic function indirectly by stimulating the release of acetylcholine from pancreatic nerves.

Amylases↗
PubMed1981

Receptors for cholecystokinin and insulin in isolated pancreatic acini: hormonal control of secretion and metabolism.

Both isolated pancreatic cells and isolated pancreatic acini have been prepared from mouse and rat pancreas. Although isolated cells are useful for the study of early events in stimulus-secretion coupling such as regulation of Ca2+ fluxes, they show a relatively poor ability to secrete digestive enzymes in response to secretagogues. Most likely this deficiency in secretion is due to the loss of specialization at the luminal plasma membrane surface. In contrast to isolated cells, isolated pancreatic acini can be used to study the secretion of digestive enzymes in response to hormones and neurotransmitters. Using isolated acini and a new preparation of radioiodinated cholecystokinin (CCK), we have been able to characterize pancreatic CCK receptors. Analysis of binding data reveals two orders of binding sites, a high affinity site (Kd = 64 pm) and a low affinity site (Kd = 21 nm). Stimulation of amylase release correlates with occupancy of the high affinity site. High affinity receptors for insulin are also present on isolated acini. After binding to these receptors, insulin stimulates protein and amylase synthesis. Insulin does not directly stimulate amylase secretion but rather potentiates the effects of hormonal secretagogues. These studies indicate, therefore, that isolated pancreatic acini can be employed to study in vitro various events in hormonal and neurotransmitter regulation of pancreatic enzyme secretion and metabolism.

Animals↗
PubMed1980

Cholecystokinin receptors in the brain: characterization and distribution.

Specific cholecystokinin binding sites in particulate fractions of rat brain were measured with iodine 125-labeled Bolton-Hunter cholecystokinin, a cholecystokinin analog that has full biological activity. Binding was detected in brain regions known to contain immunoreactive cholecystokinin. Binding was saturable, reversible, of high affinity (dissociation constant, 1.7 x 10(-9) M), and was inhibited by cholecystokinin analogs but not by unrelated hormones.

Animals↗
PubMed1980

Binding of cholecystokinin to high affinity receptors on isolated rat pancreatic acini.

The binding of cholecystokinin (CCK) to its receptors on isolated rat pancreatic acini was investigated employing high specific activity, radioiodinated CCK (125I-BH-CCK), prepared by the conjugation of 125I-Bolton-Hunter reagent (125I-BH) to CCK. Binding was specific, time-dependent, reversible, and linearly related to the acinar protein concentration. After incubation for 30 min at 37 degrees C, the 125I-BH-CCK both in the incubation medium and bound to acini remained intact, as judged by gel filtration and trichloroacetic acid precipitation studies. Scatchard analysis was compatible with two classes of binding sites on acini: a very high affinity site (Kd, 64 pM) and a lower affinity site (Kd, 21 nM). 125I-BH-CCK binding to acini was competitively inhibited by CCK and four of its analogues in proportion to their biological potencies but not by unrelated hormones. Stimulation of amylase secretion by CCK and inhibition of 125I-BH-CCK binding by the same analogues carried out under identical conditions revealed a correlation (r = 0.99) between binding potency and amylase secretion. Stimulation of amylase secretion by CCK closely paralleled the occupancy of the high affinity CCK binding sites. It is concluded that the high affinity CCK binding sites most likely are the receptors mediating the stimulation of amylase secretion by CCK.

Animals↗
PubMed1979

Preparation of biologically active radioiodinated cholecystokinin for radioreceptor assay and radioimmunoassay.

A modified method is described for the preparation of stable, high specific activity radioiodinated cholecystokinin (CCK) by its conjugation to 125I-Bolton Hunter reagent (125I-BH). Purified radioiodinated CCK (125I-BH-CCK) stimulated amylase release from isolate rat pancreatic acini with a potency identical to that of native CCK. Further, 125I-BH-CCK was highly immunoreactive and reacted with antisera directed toward both the NH2- and COOH-terminal portions of the CCK molecule. Finally, 125I-BH-CCK bound to specific receptor sites on isolated pancreatic acini.

Animals↗
PubMed1979

Experimental acute pancreatitis: action of atropine and beta-haloethylamine furoate on muscarine-induced exocrine pancreatic secretion.

Intraarterially administered muscarine induced predictable and reproducible experimental acute pancreatitis with a simultaneous increase in amylase levels in blood. Muscarine also caused a transient rise followed by a lowering of blood glucose levels. The stimulated amylase secretion was dose-response related. The guinea pigs survived 2--2 1/2 h after muscarine administration. Atropine (3 and 5 mg/kg), an antimuscarinic agent, injected intraperitoneally 2 h prior to muscarine administration, (a) inhibited muscarine-induced amylase secretion, and (b) marginally increased the survival time of guinea pigs, but could not sustain the animals for further experimentation. The high death rate of experimental animals prevented the use of this method as a model for investigation of experimental acute pancreatitis.

Acute Disease↗