An anastomotic device for microvascular surgery: evolution

A new anastomotic device is demonstrated that is suitable in microvascular surgery for repairing severed blood vessels and inserting vein grafts. Initial pilot studies indicate a 100% patency rate for vessel anastomosis, and a one-year study produced a 96% success rate. However, histological examination revealed notable vessel deterioration with a rigid device. Therefore, an absorbable anastomotic coupler was developed that demonstrates a high patency rate (92%) in both arteries and veins, with substantial absorption of the device by 70 days. Healing at the anastomotic site was qualitatively similar to that obtained with a sutured anastomosis; there was endothelialization by 14 days and absorption of the device by 70 days.

Intracellular Ca2+ and phorbol esters synergistically inhibit internalization of epidermal growth factor in pancreatic acini

The association of 125I-labelled epidermal growth factor (125I-EGF) with mouse pancreatic acinar cells was inhibited by secretagogues which increase intracellular free Ca2+ concentrations. These agents included cholecystokinin-octapeptide (CCK8) and the Ca2+ ionophore A23187. Inhibition by CCK8 was blocked by lowering the incubation temperature from 37 degrees C to 15 degrees C. Moreover, in contrast with studies of intact acini, the binding of 125I-EGF to isolated acinar membrane particles was not affected either by CCK8, or by varying the level of Ca2+ in the incubation medium. These results indicated, therefore, that the inhibition of 125I-EGF association with acinar cells required intact cells that are metabolically active. Since intact cells at 37 degrees C are known to internalize bound EGF rapidly, acid washing was used to distinguish membrane-associated hormone from internalized hormone. Under steady-state conditions 86% of the 125I-EGF associated with the acini was found to be internalized by this technique. When agents that increased intracellular Ca2+ were tested they all markedly reduced the amount of internalized hormone, whereas surface binding was only minimally affected. The phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate (TPA), which is known to activate protein kinase C, a Ca2+-regulated enzyme, also inhibited the association of EGF with acini. This inhibition was similar to that induced by elevated intracellular Ca2+. To test whether these two inhibitory phenomena were related, the effects of TPA in combination with the Ca2+ ionophore A23187 were examined. At low concentrations the effects were synergistic, whereas at high concentrations the maximal level of inhibition was not changed. We suggest therefore that elevated intracellular Ca2+ and phorbol esters may inhibit EGF internalization by a mechanism involving activation of protein kinase C.

Brain CCK receptors are structurally distinct from pancreas CCK receptors

Brain and pancreas cholecystokinin (CCK) receptors differ markedly in their selectivity for CCK analogs. To determine the size and subunit structure of the brain CCK receptor and compare it to that of the pancreas, 125I-CCK33 was covalently cross-linked with ultraviolet light to its receptor on mouse brain particles and purified pancreatic plasma membranes. When CCK was crosslinked to brain membranes, a single consistent major labeled protein band of Mr = 55,000 was observed in both the presence and the absence of DTT. These data with brain receptors contrast to results with pancreatic receptors where two bands of Mr = 120,000 and 80,000 are labeled in the absence and presence of DTT, respectively. These studies indicate, therefore, that the brain and pancreas CCK receptors are structurally and functionally distinct.

Effect of intracellular Ca2+ on insulin-like growth factor II. internalization into pancreatic acini. Roles of insulin and cholecystokinin

Previously, we reported that pancreatic acini have specific receptors for the insulin-like growth factors (IGF) I and II. We now report that the binding of 125I-labeled IGF II to mouse pancreatic acini is maximally increased by 100 nM insulin (51%) and is maximally reduced by 10 nM cholecystokinin octapeptide (CCK8) (34%), but is not affected by other regulatory peptides such as somatostatin or glucagon. Since many polypeptide hormones are internalized, we determined whether this regulation of IGF II binding occurred via a change in internalization. Acid washing or trypsinization has been shown to remove surface-bound hormone while the acid- or trypsin-resistant radioactivity represents internalized radioligand. Insulin increased and CCK8 decreased the internalization of IGF II as determined by these techniques. Studies of IGF II binding to acini at low temperature (15 degrees C) and binding to particulate fractions from acini were also consistent with the effect of insulin to increase and CCK8 to decrease the internalization of IGF II. When insulin and CCK8 were added together, the inhibitory effect of CCK8 predominated, indicating that CCK8 acted distal to the effect of insulin. Several lines of evidence suggest that this effect of CCK8 was via the CCK receptor and was mediated via a change in intracellular Ca2+: the effect of CCK8 on inhibiting IGF II binding was blocked by the cholecystokinin antagonist N2,O2'-dibutyryl cGMP; the cholinergic agent carbachol (1-100 microM), which acts through the muscarinic receptor to increase intracellular Ca2+, also inhibited IGF II binding; the Ca2+ ionophore A23187 (1-5 microM) mimicked the effects of CCK8 and carbachol. These data indicate, therefore, that CCK8 and possibly insulin may regulate the internalization of IGF II via intracellular Ca2+. Moreover, the data raise the possibility that alterations of hormone internalization may be a general phenomenon of hormone-hormone interaction.

Characterization of cholecystokinin receptors in bullfrog (Rana catesbeiana) brain and pancreas

The binding of biologically active 125I-Bolton-Hunter-CCK-33 to bullfrog brain and pancreatic membrane particles was characterized. Both tissues exhibited time-dependent, saturable, reversible, and high affinity binding without evidence for cooperative interaction. Both bullfrog CCK receptors resembled their mammalian counterparts in having acidic pH optima for tracer binding and a Kd of about 0.5 nM. However, the receptors differed from their mammalian counterparts in that (1) the bullfrog brain membranes bound more tracer per mg protein than did the pancreatic membranes, (2) both bullfrog CCK receptors were relatively insensitive to dibutyryl cGMP, and (3) both bullfrog brain and pancreatic CCK receptors exhibited the same general specificity toward a variety of CCK and gastrin peptides. For both tissues, the relative order of receptor binding potency was CCK-8 greater than caerulein = CCK-33 greater than gastrin-17-II greater than CCK-8-ns = gastrin-17-I greater than caerulein-ns greater than gastrin-4 with the sulfated CCK peptides being 1000-fold more potent than their nonsulfated analogs. Sulfated gastrin was also relatively potent, being only 10-fold weaker than CCK-8. Gastrin-4 was 20 000-fold weaker than CCK-8 in interacting with the brain CCK receptor. The latter finding is in sharp contrast to the mammalian brain CCK receptor. We conclude that the bullfrog brain and pancreas contain similar CCK receptors of probable physiological significance and may represent an ancestral condition from which the two distinct CCK receptors present in mammalian brain and pancreas have evolved.

Regulatory mechanisms in pancreas and salivary acini

Pancreas and salivary glands have highly developed regulatory mechanisms for the acute control of secretion of macromolecules and electrolytes, although other longer-term biosynthetic functions are also clearly regulated. The concepts of receptors and second messengers are clearly established, although receptors as molecular entities are just beginning to be characterized. While the functions activated are clearly organ or cell specific, the control systems clearly are not. The molecular mechanisms or effectors by which secretion is stimulated are still largely unknown. In the case of macromolecular secretion, emphasis is currently focused on cyclic AMP and Ca2+-activated phosphorylation of cellular substrates. In the case of electrolyte secretion, attention is centered on the ion channels and carriers by which ions enter cells and on the energy dependent Na-K pump which carries out active ion extrusion.

Diabetes in the rat is associated with a reversible postreceptor defect in cholecystokinin action

Diabetes in the rat is associated with a selective decrease in the sensitivity of pancreatic acini to the secretagogue cholecystokinin. In these animals the concentration of cholecystokinin-33 that maximally stimulates amylase release from isolated pancreatic acini shifts from 300 pM in normal animals to 1 nM in animals made diabetic with streptozotocin. To evaluate the role of the cholecystokinin receptor in this loss of sensitivity, specific 125I-cholecystokinin-33 binding to its receptors on acini was measured. When compared with controls, acini from diabetic rats bound more cholecystokinin at all hormone concentrations. In diabetes, the total cholecystokinin binding capacity of acini increased from 157 fmol/mg to 362 fmol/mg acinar protein. Moreover, the amount of cholecystokinin bound at a maximally stimulating cholecystokinin concentration increased fourfold from 11 to 44 fmol/mg acinar protein. When diabetes was reversed by treatment with insulin, both the altered secretory responses and the increased binding of 125I-cholecystokinin returned to normal. These data indicate, therefore, that the decreased sensitivity of pancreatic acini from diabetic rats is due to an impaired ability of receptor bound cholecystokinin to initiate its cellular response.

Bioassay of plasma cholecystokinin in rats: effects of food, trypsin inhibitor, and alcohol

We report herein a specific, sensitive, and rapid bioassay for measuring plasma cholecystokinin in rats. Plasma was first passed through octadecylsilylsilica cartridges and the extracts were then tested for their content of cholecystokinin, based on their ability to stimulate amylase release from isolated rat pancreatic acini. Plasma levels of cholecystokinin-octapeptide as low as 0.18 pM were detectable. Gastrin, in contrast, reacted only weakly in this system. Cholecystokinin bioactivity was inhibited by the antagonist dibutyryl cyclic guanosine monophosphate and was eliminated by immunoadsorption with an antibody directed against the carboxyl terminus of cholecystokinin. Plasma cholecystokinin levels in fasting rats as cholecystokinin-octapeptide equivalents were 0.31 +/- 0.05 pM (mean +/- SE) and rose to 6.2 +/- 1.8 pM after feeding. Plasma cholecystokinin levels also increased 30-fold after intragastric instillation of soybean trypsin inhibitor and 15-fold after ethanol instillation. After column chromatography of plasma, two different forms of cholecystokinin were identifiable; one eluted with the octapeptide of cholecystokinin whereas the other most abundant form was intermediate in size between cholecystokinin-33 and cholecystokinin-octapeptide.

The somatostatin receptor on isolated pancreatic acinar cell plasma membranes. Identification of subunit structure and direct regulation by cholecystokinin

Somatostatin binding to its receptors on rat pancreatic acinar membranes was characterized with [125I-Tyr1]somatostatin. Binding at 24 degrees C was rapid reaching a maximum after 60 min and was reversible upon the addition of 1 microM unlabeled ligand. Scatchard analysis revealed a single class of binding sites, with a Kd of 0.32 +/- 0.03 nM and a binding capacity of 600 +/- 54 fmol/mg of protein. Specificity for the somatostatin was demonstrated with the inhibition of labeled hormone binding by somatostatin analogs in proportion to their biological activities. When [125I-Tyr1]somatostatin was cross-linked to its receptors with the photoreactive cross-linker n-hydroxysuccinimidyl-4-azidobenzoate, the hormone was associated with Mr = 90,000 protein. Similar mobilities of the radioactive band were observed in the presence and absence of dithiothreitol. In contrast to other unrelated peptides, cholecystokinin (CCK) and its analogs directly reduced [125I-Tyr1] somatostatin binding to isolated membranes. The effect of CCK was one-half-maximal at 3 nM and maximal at 100 nM. In the presence of 3 nM CCK8, the binding capacity for somatostatin was decreased to 237 +/- 39 fmol/mg of protein without a significant change in affinity. Dibutyryl cyclic GMP, a CCK receptor antagonist, blocked this action of CCK8 indicating that the CCK receptor mediated the decrease in [125-Tyr1]somatostatin binding. In contrast cerebral cortex membranes, which also possess a somatostatin receptor, were not regulated by CCK. These results indicate, therefore, that 1) purified pancreatic acinar plasma membranes contain specific receptors for somatostatin, 2) the receptor has an apparent Mr of about 90,000, and 3) the binding of somatostatin to its receptor on pancreatic plasma membranes is regulated by CCK analogs acting via the CCK receptor.

Regulation of pancreatic acinar cell insulin receptors by insulin

In vivo pancreatic acini from normal mice are exposed to very high concentrations of insulin. To determine whether insulin receptors in these acini are downregulated by this endogenous insulin, insulin receptors on acini from both normal and diabetic mice were studied. Isolated acini from normal mice, which have accompanying islets of Langerhans, were studied under conditions where endogenous insulin was minimized. These acini bound 50% less 125I-insulin than acini from mice made diabetic with streptozotocin. Computer analysis of competition-inhibition curves showed a decrease in the number of insulin receptors in acini from normal mice when compared with acini from diabetic mice; however, the IC50 (a measure of receptor affinity) remained unchanged at approximately 1 nM. To study further the regulation of acinar cell insulin receptors, acini from diabetic mice were placed in suspension culture for 24 h. Addition of 1 microM insulin during the culture period led to a 30% decrease in subsequent 125I-insulin binding; the presence or absence of either epidermal growth factor or carbachol was without effect on insulin binding. The decrease in binding induced by insulin resulted from a change in receptor number without an alteration of the IC50. Measurement of total acinar cell insulin receptors by solubilization of these acini in 1% Triton X-100 showed that this insulin-induced decrease was due to a change in the total number of cellular insulin receptors. The present study suggests, therefore, that insulin can regulate its own receptor on pancreatic acini and that in vivo insulin receptors in normal pancreatic cells are downregulated, presumably due to high ambient insulin concentrations.

Methylamine and monensin do not block insulin internalization but do influence the intracellular distribution and action of insulin in pancreatic acini from diabetic mice

Methylamine and monensin are two agents known to interfere with the recycling of membrane receptors. In the present investigation, we studied their effects on the binding, intracellular distribution, and action of insulin in isolated pancreatic acini prepared from diabetic mice. These drugs had several similar effects on these cells. In a dose-dependent fashion, both increased the amount of [125I]insulin associated with acini. Methylamine approximately doubled and monensin tripled the amount of insulin associated with cells. Employing electron microscope autoradiographs, we observed the accumulation of hormone in large vacuoles in the Golgi-lysosomal area after treatment with methylamine and in smaller swollen Golgi vesicles after treatment with monensin. The influences of both agents on the biological effects of insulin in acini were then investigated. Both agents blocked insulin stimulation of [3H]2-deoxy-D-glucose uptake in acini. The effect of methylamine was also studied on [3H]leucine incorporation into protein and was found to only partially block the effect of insulin. Since insulin and its receptor are internalized, it is likely that the accumulation of insulin in acini induced by these two agents was due to their inhibition of the cellular processing of insulin and its receptor. Moreover, the effects of these two agents to inhibit insulin-stimulated glucose transport may have resulted from either the inhibition of the recruitment of glucose carriers from the Golgi to the plasma membrane or an abnormal interaction of internalized insulin with the Golgi.

The effect of long-distance running upon appendicular bone mineral content

The bone mineral content (BMC) of the os calcis was measured for a group of 20 male runners at the beginning and the end of a 9-month marathon training program. The participants had no previous running experience. The percent change in bone mineral in the runners was compared with that of a control group of male subjects of the same age range (38-68 yr). The consistent runners showed a significant increase in bone mineral over that of the controls; the increase was not significant for inconsistent runners. The data suggest that those runners with longer, more consistent distances gained more bone mineral than those with shorter, more inconsistent distances.

Activation of protein kinase activity in pancreatic acini by calcium and cAMP

Regulation of protein kinase activity by calcium and cAMP was investigated in cytosolic and particulate preparations from isolated mouse pancreatic acini. In cytosol, three protein kinase activities could be distinguished: a calcium-activated kinase activity that was increased by exogenous calmodulin (CaM) and abolished by treatment of cytosol with a phenothiazine-coupled resin, a calcium-activated kinase activity dependent on phosphatidylserine (PS), and cAMP-activated kinase activity. Phosphorylation of a Mr = 92,000 cytosolic protein was greatly increased by both CaM-dependent and cAMP-activated kinases, whereas PS-dependent kinase activity most heavily phosphorylated proteins of Mr = 62,000 and 40,000. In addition, these kinase activities demonstrated differences in specificity for exogenous protein substrates. CaM-and PS-dependent kinases were completely blocked by trifluoperazine; the inhibitor protein of cAMP-activated protein kinase selectively inhibited cAMP-activated kinase activity. Exogenous CaM decreased the concentration of free calcium for half-maximal activation of CaM-dependent kinase activity from 5.5 +/- 0.5 to 1.2 +/- 0.3 microM Ca2+; half-maximal activation of the PS-dependent and cAMP-activated kinase activities was achieved at 12 microM Ca2+ and 40-50 nM cAMP, respectively. In a particulate fraction depleted of endogenous CaM, CaM-dependent and cAMP-activated kinase activities were detected. In conclusion, this study demonstrates the existence of protein kinases in pancreatic acini which may be involved in the action of pancreatic regulatory agents that use calcium or cAMP as an intracellular messenger.

Interaction of cholecystokinin and vasoactive intestinal polypeptide on function of mouse pancreatic acini in vitro

In isolated mouse pancreatic acini, vasoactive intestinal polypeptide (VIP) and secretin potentiated amylase release stimulated by cholecystokinin (CCK). VIP (1-100 nM) or secretin (100-1000 nM) alone elicited a negligible secretory response, whereas in combination with CCK, these agents induced a significantly larger response. VIP increased maximal amylase release elicited by CCK without affecting the potency with which CCK stimulated secretion. The phosphodiesterase inhibitor, 3-isobutyl-1-methyl xanthine (IBMX), from 0.03-1.0 mM had effects on secretion similar to those of VIP. VIP, IBMX and 8-Br-cyclic AMP, all of which act through or mimic the action of cyclic AMP, potentiated the secretory response to maximal concentrations of CCK, carbamylcholine and the ionophore A23187, all of which act via intracellular calcium. In contrast to amylase release, stimulation of acinar glucose transport by CCK or carbamylcholine was not augmented by VIP, secretin, IBMX or 8-Br-cyclic AMP. The results indicate that for amylase release from mouse pancreas, secretagogues acting via cyclic AMP potentiate those acting via calcium. However, potentiation does not apply to all biological responses of the pancreatic acinus and each response must be studied individually.

Amylase secretion by isolated pancreatic acini after acute cholecystokinin treatment in vivo

A single dose of synthetic cholecystokinin octapeptide (CCK8, 5 micrograms/kg) in a depot carrier was injected subcutaneously into rats 2 and 14 h before the removal of the pancreas and the preparation of isolated pancreatic acini. CCK8 treatment induced no significant change in body weight or total amount of pancreatic DNA, but pancreatic weight, total pancreatic protein and amylase, and the concentration of amylase and total protein relative to DNA were significantly decreased. In acini prepared from CCK8-pretreated rats, responsiveness to maximal and supramaximal concentrations of CCK8 was significantly increased, irrespective of whether the amount of amylase released was expressed relative to DNA or calculated as a percentage of the acinar content. The dose-response curves for CCK8 were similarly shaped in both CCK8-pretreated and control rats but shifted threefold toward higher concentrations of CCK8 2 or 14 h after CCK8 treatment. Specific 125I-CCK binding was significantly increased only for high-affinity binding sites. Although these observations suggest that alterations in pancreatic amylase release could be due to changes at the cholecystokinin receptor, the secretory responsiveness to maximal and supramaximal concentrations of carbachol was also increased without any change in the sensitivity. Moreover, in contrast to the cholecystokinin receptor, there was no change in the number of muscarinic receptors or in their affinity for either agonists or antagonists measured with [3H]quinuclidinyl benzilate.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo localization of insulin binding to cells of the rat pancreas

The uptake of 125I-insulin by rat pancreas was studied in vivo. Following fixation and light microscope autoradiography, saturable uptake of 125I-insulin was quantitatively demonstrated on acinar and duct cells but not on blood vessels and islets of Langerhans. Electron microscopy revealed the localization of 125I-insulin to the basolateral cell membranes of acinar and duct cells.

Cholecystokinin and insulin regulate insulin-like growth factor II binding to pancreatic receptors; evidence of a role for intracellular calcium

The binding of 125I-labeled insulin-like growth factor II (125I-IGF II) to mouse pancreatic acini was stimulated (45%) by insulin and inhibited (30%) by cholecystokinin octapeptide (CCK8). When CCK8 and insulin were added together, the effect on IGF II binding was similar to that seen when CCK8 was added alone. Two lines of evidence suggest that this effect of cholecystokinin on basal and insulin-stimulated 125I-IGF II binding was mediated via a change in intracellular calcium: (1) the cholinergic agent carbachol inhibited IGF II binding to its receptors; (2) addition of the Ca2+ ionophore A23187 mimicked the effects of CCK8 and carbachol. In contrast to its effects on IGF II binding to acini, CCK8 had only small effects on IGF I binding and no effects on insulin binding.

Pancreatic CCK receptors: characterization of covalently labeled subunits

125I-CCK was crosslinked with ultraviolet light to its receptor on pancreatic plasma membranes. The predominant labeled species following polyacrylamide gel electrophoresis had a molecular weight of 120,000 in the absence, and 80,000 in the presence of the reducing agent dithiothreitol. The M = 120,000 labeled band could be extracted, reduced and converted to Mr = 80,000. Moreover, peptide mapping with Staph aureus V8 protease showed a similar pattern for the 120,000 and 80,000 dalton bands. The crosslinked receptor could be solubilized with Triton X-100, absorbed to wheat germ agglutinin and eluted with N-acetylglucosamine. The results indicate, therefore, that the CCK receptor is a glycoprotein with subunits coupled by disulfide bonds.

Insulinlike growth factors bind to specific receptors in isolated pancreatic acini

Recently we have demonstrated the existence of specific receptors for insulin on pancreatic acini. Employing 125I-labeled insulinlike growth factors (IGFs) and insulin, we report the existence of distinct receptors for IGF-I and IGF-II on mouse pancreatic acini. Insulin competes with 125I-IGF-I with 1,000-fold less potency. By contrast, insulin increases the binding of 125I-IGF-II to its receptor. IGF in turn inhibits 125I-insulin binding to its receptor but with 250-fold less potency. Thus, distinct receptors exist on acini for IGF-I, IGF-II, and insulin. Moreover, IGF, like insulin, stimulates sugar transport by acini. The mechanism of IGF stimulation may be similar to insulin, as the effect of maximal concentrations of the two peptides when added together is not additive. These results raise the possibility, therefore, that IGFs may be a new class of physiological regulators of pancreatic acinar cell function.

Rubidium in psychiatry: research implications

A brief overview of the use of rubidium in affective disorders and schizophrenia is presented. Although antidepressant action of rubidium has not been supported by adequate number of controlled studies, its potential contribution to psychiatry warrants further investigations. Endogenous rubidium may be a useful research tool in the future psychopharmacological studies of affective disorders.

Stimulus-secretion coupling in pancreatic acinar cells

Figure 4 summarizes the steps by which Ca2+ and cyclic AMP-mediated secretagogues activate enzyme secretion in the pancreatic acinar cell. CCK and acetylcholine bind to specific plasma membrane receptors and through an as yet incompletely understood mechanism give rise to an elevation in free cytoplasmic Ca2+. A question central to this scheme is whether receptor binding leads to intracellular Ca2+ mobilization through generation of a diffusable mediator. Clues to answering this question may come from a) determining whether Ca2+ is released from the plasma membrane in addition to one or more intracellular organelles, and b) examining the role (if any) of membrane phosphatidylinositol metabolism in Ca2+ mobilization. A second class of secretagogues, represented by VIP and secretin, bind to their specific receptors and cause the accumulation of cyclic AMP. Cyclic AMP potentiates Ca2+ in activating secretion, and in some species, cyclic AMP may activate secretion independently of Ca2+. Ca2+ may act by regulating the activity of calmodulin dependent protein kinase(s) and phosphatase(s) and a phospholipid dependent kinase (protein kinase C) which has also been shown to be activated by diacylglycerol; cyclic AMP activates a distinct kinase termed protein kinase A. These kinases and phosphatases then alter the phosphorylation of specific proteins which are presumed to play structural or regulatory roles in exocytosis. Potentiation may thus result from interaction of Ca2+ and cyclic AMP at the level of a protein kinase, phosphatase or protein substrate.

Degradation of insulin by isolated mouse pancreatic acini. Evidence for cell surface protease activity

In the present study, we have used isolated mouse pancreatic acini to investigate the relationship between 125I-insulin binding and its degradation in order to probe the nature and cellular localization of the degradative process. In these cells, the proteolysis of 125I-insulin was dependent on time and cell concentration, and was saturated by unlabeled insulin with a Km of 290 nM. Since this value was much higher than the Kd for insulin binding to its receptor (1.1 nM), the data indicated that 125I-insulin degradation by acini occurred primarily via nonreceptor mechanisms. Several lines of evidence suggested that insulin was being degraded by the neutral thiol protease, insulin degrading enzyme (IDE). First, insulin degradation was inhibited by thiolreacting agents such as N-ethylmaleimide and p-chloromercuribenzoate. Second, the Km for degradation in acini was similar to the reported Km for IDE in other tissues. Third, the enzyme activity had a relative mol wt of approximately 130,000 by gel filtration, a value similar to that reported for purified IDE. Fourth, the degrading activity was removed with a specific antibody to IDE. Other lines of evidence suggested that enzymes located on the cell surface played a role in insulin degradation by acini. First, the nonpenetrating sulfhydryl reacting agent 5,5' dithiobis-2-nitrobenzoic acid blocked 125I-insulin degradation. Second, a specific antibody to IDE identified the presence of the enzyme on the cell surface. Third, chloroquine, leupeptin and antipain, agents that inhibit lysosomal function, did not influence 125I-insulin degradation. Fourth, highly purified pancreatic plasma membranes degraded 125I-insulin.

Binding specificity of the mouse cerebral cortex receptor for small cholecystokinin peptides

Prior studies have shown that the cerebral cortex cholecystokinin (CCK) receptor can bind CCK and gastrin analogs with high affinity. In the present work the brain CCK receptor had approximately a three times greater affinity for CCK8 than its C-terminal tetrapeptide (CCK4) while the C-terminal tripeptide (CCK3) was 1000-fold less potent than CCK4. Thus the C-terminal tetrapeptide appears to be the minimal C-terminal CCK sequence required for high affinity binding. Since brain membranes degrade various peptides including CCK, we also evaluated the stability of CCK analogs under the conditions used to measure receptor binding by the following three methods: (1) Studies of degradation-resistant analogs in binding assays; (2) analysis of analog degradation by high performance liquid chromatography (HPLC); and (3) determination of the change in potency of CCK analogs in competitive binding studies subsequent to preincubation with brain membranes. These studies indicated that degradation of analogs by the brain membranes although significant did not account for the differences in potency of analogs in competitive binding studies. Therefore, the observed differences in potencies of the analogs tested are due to the receptor affinity and not sensitivity of the analog to degradation.