The active site cysteine of the proapoptotic protein glyceraldehyde-3-phosphate dehydrogenase is essential in oxidative stress-induced aggregation and cell death

Recent studies have revealed that the redox-sensitive glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), is involved in neuronal cell death that is triggered by oxidative stress. GAPDH is locally deposited in disulfide-bonded aggregates at lesion sites in certain neurodegenerative diseases. In this study, we investigated the molecular mechanism that underlies oxidative stress-induced aggregation of GAPDH and the relationship between structural abnormalities in GAPDH and cell death. Under nonreducing in vitro conditions, oxidants induced oligomerization and insoluble aggregation of GAPDH via the formation of intermolecular disulfide bonds. Because GAPDH has four cysteine residues, including the active site Cys(149), we prepared the cysteine-substituted mutants C149S, C153S, C244A, C281S, and C149S/C281S to identify which is responsible for disulfide-bonded aggregation. Whereas the aggregation levels of C281S were reduced compared with the wild-type enzyme, neither C149S nor C149S/C281S aggregated, suggesting that the active site cysteine plays an essential role. Oxidants also caused conformational changes in GAPDH concomitant with an increase in beta-sheet content; these abnormal conformations specifically led to amyloid-like fibril formation via disulfide bonds, including Cys(149). Additionally, continuous exposure of GAPDH-overexpressing HeLa cells to oxidants produced disulfide bonds in GAPDH leading to both detergent-insoluble and thioflavin-S-positive aggregates, which were associated with oxidative stress-induced cell death. Thus, oxidative stresses induce amyloid-like aggregation of GAPDH via aberrant disulfide bonds of the active site cysteine, and the formation of such abnormal aggregates promotes cell death.

Essential role of nitric oxide in descending inhibition in the rat proximal colon

Possible mediators of descending inhibition in the rat proximal colon were studied. Localized distension with a small balloon caused relaxation of the circular muscle on the anal side of the distended region. This relaxation was still observed after the colonic segment had been desensitized to ATP, neurotensin and vasoactive intestinal peptide, so these compounds seem unlikely to mediate descending inhibition. Nitro-arginine inhibited the relaxation induced by the distension, and L-arginine counteracted the effect of nitro-arginine. Nitric oxide, isoamylnitrate and sodium nitroprusside caused relaxation. These results strongly suggest an essential role of nitric oxide in descending relaxation in the rat proximal colon.

Specific localization of an inwardly rectifying K(+) channel, Kir4.1, at the apical membrane of rat gastric parietal cells; its possible involvement in K(+) recycling for the H(+)-K(+)-pump

Hydrochloric acid (HCl) is produced in parietal cells of gastric epithelium by a H(+)-K(+) pump. Protons are secreted into the gastric lumen in exchange for K(+) by the action of the H(+)-K(+)-ATPase. Luminal K(+) is essential for the operation of the pump and is thought to be supplied by unidentified K(+) channels localized at the apical membrane of parietal cells. In this study, we showed that histamine- and carbachol-induced acid secretion from isolated parietal cells monitored by intracellular accumulation of aminopyrine was depressed by Ba(2+), an inhibitor of inwardly rectifying K(+) channels. Among members of the inwardly rectifying K(+) channel family, we found with reverse transcriptase-polymerase chain reaction analyses that Kir4.1, Kir4.2 and Kir7.1 were expressed in rat gastric mucosa. With immunohistochemical analyses, Kir4.1 was found to be expressed in gastric parietal cells and localized specifically at their apical membrane. The current flowing through Kir4.1 channel expressed in HEK293T cells was not affected by reduction of extracellular pH from 7.4 to 3. These results suggest that Kir4.1 may be involved in the K(+) recycling pathway in the apical membrane which is required for activation of the H(+)-K(+) pump in gastric parietal cells.

VIP- and PACAP-mediated nonadrenergic, noncholinergic inhibition in longitudinal muscle of rat distal colon: involvement of activation of charybdotoxin- and apamin-sensitive K+ channels

1. The mediators of nonadrenergic, noncholinergic (NANC) inhibitory responses in longitudinal muscle of rat distal colon were studied. 2. An antagonist of pituitary adenylate cyclase activating peptide (PACAP) receptors, PACAP6-38, concentration-dependently inhibited the rapid relaxation of the longitudinal muscle induced by electrical field stimulation (EFS), resulting in a maximal inhibition of 47% at 3 microM. 3. PACAP6-38 inhibited the relaxation by 75% in the presence of the vasoactive intestinal peptide (VIP) receptor antagonist, VIP10-28 at 3 microM, which inhibited the relaxation by 44%. 4. An antagonist of large conductance Ca(2+)-activated K+ channels, charybdotoxin, concentration-dependently inhibited the rapid relaxation of the longitudinal muscle, resulting in a maximal inhibition of 58% at 100 nM. 5. An antagonist of small conductance Ca(2+)-activated K+ channels, apamin, concentration-dependently inhibited the relaxation (58% at 1 microM). 6. Treatment with both K+ channel antagonists resulted in 84% inhibition of the EFS-induced relaxation, which is comparable to the extent of inhibition induced by PACAP6-38 plus VIP10-28. 7. The inhibitory effect of VIP10-28 and of apamin, but not of charybdotoxin was additive: the same applied to PACAP6-38 and charybdotoxin, but not apamin. 8. Exogenously added VIP (100 nM 1 microM) induced a slow gradual relaxation of the longitudinal muscle. Charybdotoxin, but not apamin significantly inhibited the VIP-induced relaxation VIP10-28, but not PACAP6-38 selectively inhibited the VIP-induced relaxation. 9. Exogenously added PACAP (10-100 nM) also induced slow relaxation. Apamin and to a lesser extent, charybdotoxin, inhibited the PACAP-induced relaxation. PACAP6-38, but not VIP10-28 selectively inhibited the PACAP-induced relaxation. 10. Apamin at 100 nM inhibited inhibitory junction potentials (i.j.ps) induced by a single pulse of EFS Apamin also inhibited a rapid phase, but not a delayed phase of i.j.ps induced by two pulses at 10 Hz. VIP10-28 did not inhibit i.j.ps induced by a single pulse, but significantly inhibited the delayed phase at two pulses. A combination of apamin and VIP10-28 abolished the i.j.ps induced by two pulses. 11. Both VIP and PACAP induced slow hyperpolarization of the cell membrane of the longitudinal muscle. Apamin inhibited the PACAP-, but not VIP-induced hyperpolarization. 12. From these findings it is suggested that VIP and PACAP are involved in NANC inhibitory responses of longitudinal muscle of the rat distal colon via activation of charybdotoxin- and apamin-sensitive K+ channels, respectively.

Critical role of sulfenic acid formation of thiols in the inactivation of glyceraldehyde-3-phosphate dehydrogenase by nitric oxide

The relationship between possible modifications of the thiol groups of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by nitric oxide (NO) and modified enzyme activity was examined. There are 16 free thiols, including 4 active site thiols, in a tetramer of GAPDH molecule. NO donors, sodium nitroprusside (SNP), and S-nitroso-N-acetyl-DL-penicillamine (SNAP) decreased the number of free thiols with a concomitant inhibition of GAPDH activity in a concentration- and time-dependent manner. After treatment for 30 min, free thiols were maximally decreased to 8-10 per GAPDH tetramer and enzyme activity was also inhibited to 5-10% of control activity. In the presence of 30 mM dithiothreitol (DTT), these effects were completely blocked. Since similar results were obtained in the case of hydrogen peroxide (H2O2) treatment, which is known to oxidize the thiols, these effects of nitric oxide donors were probably due to modification of thiol groups present in a GAPDH molecule. On the other hand, DTT posttreatment after the treatment of GAPDH with SNP, SNAP, or H2O2 did not completely restore the modified thiols and the inhibited enzyme activity. DTT posttreatment after the 30-min-treatment with these agents restored free thiols to 14 in all treatments. In the case of SNAP treatment, all 4 active sites were restored and enzyme activity reached more than 80% of the control activity, but in two other cases one active site remained modified and enzyme activity was restored to about only 20%. Therefore, all 4 free thiols in the active site seem to be very important for full enzyme activity. DTT posttreatment in the presence of sodium arsenite, which is known to reduce sulfenic acid to thiol, almost completely restored both thiol groups and enzyme activity. These findings suggest that nitric oxide inhibits GAPDH activity by modifications of the thiols which are essential for this activity, and that the modification includes formation of sulfenic acid, which is not restored by DTT. S-nitrosylation, which is one type of thiol modification by NO, occurred when GAPDH was treated with SNAP but not SNP. Analysis of thiol modification showed that SNAP preferentially nitrosylated the active site thiols, the nitrosylation of which fully disappeared by DTT posttreatment. It seems that SNAP nitrosylates the active site thiols of GAPDH to prevent these thiols from oxidizing to sulfenic acid.

Localization of Ca2+-activated K+ channel, SK3, in fibroblast-like cells forming gap junctions with smooth muscle cells in the mouse small intestine

In the present study, we examined the expression and the localization of apamin-sensitive small conductance Ca(2+)-activated K(+) channels (SK channels) in the mouse intestine. SK3-immunoreactivity (IR) was detected in both ileum and colon. Double staining experiments showed that SK3-IR was colocalized with prolyl 4-hydroxylase (PH(alpha))-IR, but not with c-Kit-IR which are markers of fibroblast cells and the interstitial cells of Cajal (ICC), respectively. Although SK3-IR was colocalized with vimentin-IR, which is another marker of ICC, the reactivity of SK3-immunopositive cells was weaker than that of ICC. The SK3-immunopositive cells were similarly present in the intestine of c-Kit mutant mice (W/W(V)), in which ICC were absent, and its wild-type mice. The immuno-electron microscopic analysis indicated that SK3 was localized in the cells that had some similar morphological features to ICC, but obviously different from ICC. The SK3-immunopositive cells had gap junctions with the smooth muscle cells. The gap junctions were smaller than those between ICC and smooth muscle cells. These results indicate expression of SK3 in fibroblast-like cells, but not in ICC, and suggest participation of the cells in the intestinal motility.

Expression of Ca(2+)-activated K(+) channels, SK3, in the interstitial cells of Cajal in the gastrointestinal tract

A role for small-conductance Ca(2+)-activated K(+) (SK) channels on spontaneous motility of the gastrointestinal tract has been suggested. Although four subtypes of SK channels were identified in mammalian tissues, the subtypes of SK channel expressed in the gastrointestinal tract are still unknown. In this study, we investigated the expression and localization of SK channels in the gastrointestinal tract. RT-PCR analysis shows expression of SK3 and SK4 mRNA, but not SK1 or SK2 mRNA, in the rat intestine. SK3 immunoreactivity was detected in the myenteric plexus and muscular layers of the stomach, ileum, and colon. SK3-immunoreactive cells were stained with antibody for c-kit, a marker for the interstitial cells of Cajal (ICC), but not with that for glial fibrillary acidic protein in the ileum and stomach. Immunoelectron microscopic analysis indicates that SK3 channels are localized on processes of ICC that are located close to the myenteric plexus between the longitudinal and circular muscle layers and within the muscular layers. Because ICC have been identified as pacemaker cells and are known to play a major role in generating the regular motility of the gastrointestinal tract, these results suggest that SK3 channels, which are expressed specifically in ICC, play an important role in generating a rhythmic pacemaker current in the gastrointestinal tract.

Key roles of nitric oxide and cyclic GMP in nonadrenergic and noncholinergic inhibition in rat ileum

Nonadrenergic and noncholinergic (NANC) inhibitory responses in circular and longitudinal muscles of the rat ileum were studied separately in vitro. Localized distension with a small balloon caused relaxation of the circular muscle on the anal side of the distended region. Nitro-arginine inhibited the relaxation and L-arginine counteracted the effect of nitro-arginine. Treatment of the preparation with superoxide dismutase (SOD) and methylene blue resulted in enhancement and inhibition, respectively, of the relaxation induced by distension. Nitric oxide caused relaxation of the circular muscle in a dose-dependent manner. 8-Bromo cyclic GMP (cGMP) caused relaxation of the circular muscle. Electrical transmural stimulation caused relaxation followed by a rebound contraction of the longitudinal muscle. Nitro-arginine inhibited the relaxation and L-arginine counteracted this inhibition. Similar results to those in the circular muscle were obtained in the longitudinal muscle with SOD, methylene blue, nitric oxide and 8-bromo cGMP. Electrical field stimulation increased the cGMP content of the longitudinal muscle preparation. Nitric oxide also increased the cGMP content of smooth muscle cells obtained from circular and longitudinal muscles of rat ileum. Preincubation of smooth muscle cells with methylene blue inhibited the effect of nitric oxide on the cGMP content. These results suggest a key role of cGMP in NANC inhibitory responses in rat ileum. The factors mediating the responses are discussed.

Mediators of nonadrenergic, noncholinergic inhibition in the proximal, middle and distal regions of rat colon

1. The mediators of non-adrenergic non-cholinergic (NANC) relaxation of the longitudinal muscle of rat proximal, middle and distal colon were examined in vitro. 2. Electrical transmural stimulation (TMS) of proximal, middle and distal segments of rat colon induced NANC relaxations which were inhibited by tetrodotoxin (1 microM), but not by atropine (1 microM) or guanethidine (4 microM). 3. In the proximal colon, L-nitro-arginine (N5-nitroamidino-L-2,5-diaminopentanoic acid) inhibited the TMS-induced NANC relaxation and L-arginine (1 mM) reversed this inhibition. Nitric oxide (0.3-10 microM) induced relaxation of the proximal segment. 4. NANC relaxation of the proximal segments was still evident after desensitization to vasoactive intestinal peptide (VIP). A VIP antagonist (VIP 10-28, 10 microM) had no effect on the TMS-induced NANC relaxation, which was also resistant to alpha-chymotrypsin (2 units ml-1) and a substance P antagonist ([D-Pro2, D-Trp7,9]substance P, 1 microM). 5. In the middle colon, L-nitro-arginine did not inhibit the TMS-induced NANC relaxation in 6 of 9 preparations tested and partially inhibited the relaxation in the other 3 preparations. L-Arginine did not reverse the partial inhibition. 6. Complete desensitization to VIP was not achieved in the middle colon. The VIP antagonist had no effect on the TMS-induced NANC relaxation. After alpha-chymotrypsin treatment of the segment, desensitization of the segments to substance P, or in the presence of the substance P antagonist, the TMS-induced NANC relaxation was augmented. 7. In the distal colon, L-nitro-arginine did not have any significant effect on the TMS-induced relaxation and nitric oxide did not induce relaxation. The VIP antagonist significantly inhibited TMS-induced NANC relaxation. Alpa-Chymotrypsin-treatment of the distal segments resulted in significant inhibition of NANC relaxation. No desensitization to substance P was achieved. Treatment with the substance P antagonist had no effect. 8. These results suggest that nitric oxide is the mediator of the NANC inhibitory response in the proximal region of rat colon; in the middle colon, substance P acts as an excitatory neurotransmitter, antagonizing the NANC relaxation caused by the mediator of the response, which is still uncertain. Our results suggest that that VIP is the most likely candidate as a NANC transmitter in the distal colon.

Vascular anatomy of the pancreaticoduodenal region: A review

Vascular anatomy of the pancreaticoduodenal region has been the subject of numerous studies. However, several essential areas of confusion remain in interpretation of the vascular configuration. We note and discuss three key points in relation to this confusion: (1) a missing vascular arcade, (2) a rearrangement of the arcade by collateral and/or transverse vessels, and (3) a solitary vessel without an accompanying comites vein or artery. In addition, we consider that different interpretations as well as varying reported incidences depend on different "thresholds" when observations are made. Consideration of new aspects of vascular anatomy of the pancreaticoduodenal region is required for further improvement of surgical procedures. In terms of the selection of lymph node resection procedure, we discuss mainly the inferior arterial origin. Special attention should be paid to the ligation of inferior arteries because of the high incidence of the common trunk formation of the upper jejunal and inferior pancreaticoduodenal arteries. With regard to duodenum-preserving pancreatic head resection for benign tumors, our observations are introduced in view of either arterial or venous configuration. First, a communicating artery between the anterior and posterior arterial arcades is noted because of its possible critical role in blood supply to the papilla of Vater. Second, a venous drainage route from the duodenum to the retroperitoneal space in "normal" specimens is described.

Inhibition of skeletal muscle sarcoplasmic reticulum Ca2+-ATPase by nitric oxide

The effects of nitric oxide on the activities of thapsigargin-sensitive sarcoplasmic reticulum Ca2+-ATPase (SERCA) and Ca2+ uptake by sarcoplasmic reticulum (SR) membranes prepared from white skeletal muscle of rabbit femoral muscle were studied. Pretreatment of the SR preparations with nitric oxide at concentrations of up to 250 microM for 1 min decreased the SERCA activity concentration dependently, and also decreased their Ca2+ uptake. Both these effects of nitric oxide were reversible. Inhibitors of guanylyl cyclase and protein kinase G (PKG) had no significant effect on the nitric oxide-induced inhibitions of SERCA and Ca2+ uptake. Moreover, dithiothreitol did not reverse the inhibitory effects of nitric oxide on SERCA and Ca2+ uptake. These findings suggest that nitric oxide inhibits SERCA, mainly SERCA 1, of rabbit femoral skeletal muscle by an action independent of the cyclic GMP-PKG system or oxidation of thiols, and probably by a direct action on SERCA protein.

The interactions of bromocriptine and lergotrile with dopamine and alpha-adrenergic receptors

Bromocriptine and lergotrile, which are clinically used as antiparkinsonian (AP) agents, compete for the binding of H3-dopamine, H3-apomorphine, and H3-haloperidol to striatal membrane sites. Lergotrile has a higher affinity for the H3-dopamine binding to bovine striatal membranes than bromocriptine. Lergotrile and bromocriptine are almost equipotent in competing for the binding of H3-apomorphine to rat striatal membranes, but bromocriptine is more potent in competing for the binding of H3-haloperidol than lergotrile. These results indicate that lergotrile and bromocriptine are mixed putative agonist-antagonist with respect to the postsynaptic dopamine receptors. Lergotrile and bromocriptine at higher concentrations inhibit synaptosomal tyrosine hydroxylase activity, and reverse the apomorphine elicited enzyme inhibition. Thus, these ergot alkaloids behave as mixed agonist-antagonist also with respect to the presynaptic dopamine receptors. Bromocriptine and lergotrile, as well as other tested DH-ergot alkaloids and neuroleptics, compete for the binding of the alpha-antagonist H3-WB-4101 to rat cerebral cortical membranes. The displacing potencies of the tested DH-ergot alkaloids and of the neuroleptics indicate that they have a high affinity for the alpha-adrenoreceptors in the CNS.

Glycation of cataractous lens in non-diabetic senile subjects and in diabetic patients

Early- and advanced-stage products in the Maillard reaction, glycation, were measured in patients with diabetic or senile cataracts. Early-stage products were measured by means of furosine, which is an acid-hydrolysis product derived from fructose-lysine. Advanced-stage products were measured by fluorometry using high-performance liquid chromatography. Furosine levels were high (listed in descending order) in capsule, cortex and nucleus in both diabetic and senile cataracts. The advanced-stage products were also high (listed in descending order) in nucleus, cortex and capsule in both diabetic and senile cataracts. These results suggest that advanced-stage products might accumulate in larger amounts in the nucleus and cortex than in the capsule, resulting in the formation of cataracts. The study also revealed that the Maillard reaction plays an important role in causing not only diabetic cataracts but also senile cataracts.

Identification of segments VI and VII of the liver based on the ramification patterns of the intrahepatic portal and hepatic veins

We describe the pattern of intrahepatic vessel ramification in the right posterior hepatic sector in a population of 197 adults. Each specimen was dissected from its visceral (inferior) surface in order to demonstrate variations in the distribution of the portal vein branches to the hepatic segments of the right lobe, especially to segments VI (S6) and VII (S7) as described by Couinaud. We also examine whether three hepatic veins, i.e., the right hepatic vein (RHV), middle hepatic vein (MHV), and the short hepatic vein (SHV), aid the identification of segmental portal branches in the lower posterior sector. Four major patterns of branching of the posterior sectorial trunk of the portal vein system are described. In group A (32.0%) a single posterior trunk formed an arch-like pattern sending multiple branches to S6 and S7 (P6 and P7). We named the multiple branches to the apparent S6 the inferoposterior portal branches. It was difficult to identify which of these branches were equivalent to P6. In group B (27.9%), the posterior sectorial trunk bifurcated to form P6 and P7. In most of the specimens in this group, therefore, we were able clearly to identify both S6 and S7 based on the portal vein system. In group C (6.6%), the trunk trifurcated to form P6, P7, and an intermediate branch, which supplied both segments or a gray zone between them. Group D (33.5%) included variations of the anterior segmental branches, and in specimens of this group, the anteromedial border of the sector was difficult to identify. Notably, the three-dimensional interdigitating topographical relationship of the hepatic veins and the portal branches was not evident in the lower posterior sector, since tributaries of the RHV and the portal branches followed similar courses and paralleled each other in the region and since the territory of the SHV was usually restricted to the superficial parenchyma near the inferior surface. In group A, tributaries of the RHV/SHV (>3 mm in diameter) passed between the inferoposterior portal branches in only 22.2%/14.3% of the specimens. Thus the hepatic veins often did not reveal which of the multiple inferoposterior branches was P6. Moreover, in the subset of Group B in which the segments were identified based on the portal vein ramification, tributaries of the RHV/SHV (>3 mm in diameter) showed the intersegmental interdigitating arrangement in only 32.0%/6.0% of the specimens. In addition, a thick tributary of the MHV, sometimes arising from S6, did not run along, but penetrated the S5/S6 border plane from the lateral to the medial side. Therefore, the three hepatic veins (RHV, SHV, MHV) often did not aid the identification of the liver segments in the region. Consequently, the less than ideal combinations of irregular configurations of the portal and hepatic venous systems suggest that the right posterior segments cannot be conclusively identified anatomically in 30-40% of cases. Other means of identification, such as the conventional proportional manner (the upper and lower halves of the posterior sector roughly correspond to S6 and S7) may be required.

Distribution of PNMT and epinephrine in the medulla oblongata of normotensive and spontaneous hypertensive rats

The distribution of the Epinephrine forming enzyme (PNMT) activity and Epinephrine (E) levels was investigated in the medulla oblongata of spontaneous hypertensive rats (SH-rats) and in two normotensive strains, namely Wistar Kyoto rats (WK-rats) and Wistar rats. The PNMT activity increases progressively from the caudal to rostral parts in the C1 and C2 regions of the medulla oblongata. The enzyme activity and the E levels are in all parts of the C1 and C2 regions higher in Wistar rats than in WK-rats. The PNMT activity in all parts of the C2 region (with the exception of the caudal region), and in the middle part of the C1 region is higher in SH-rats than in WK-rats. The E levels in the SH-rats are higher than in WK-rats in the mediocaudal parts of the C2 and C1 regions.

Nitric oxide-mediated relaxation without concomitant changes in cyclic GMP content of rat proximal colon

1. We studied the relation of nitric oxide-mediated relaxation of longitudinal muscle to changes in cyclic GMP content of the tissue in the proximal colon of rats. 2. Dimethylphenylpiperazinium (DMPP) and electrical field stimulation (EFS) induced nitric oxide-mediated relaxation of the segments with a concomitant increase in cyclic GMP content. 3. LY 83583 and methylene blue, soluble guanylyl cyclase inhibitors, significantly inhibited the stimulatory effects of DMPP and EFS on the cyclic GMP content, but did not affect the relaxant responses of the segments to DMPP and EFS. 4. Rp-8 bromo cyclic GMPS, an inhibitor of cyclic GMP-dependent protein kinase had no effect on DMPP- and EFS-induced relaxation. 5. These data strongly suggested that nitric oxide-mediated relaxation of the rat proximal colon is not associated with change in cyclic GMP content of the tissue.

beta-Adrenoceptor alterations coupled with secretory response in rat parotid tissue

Simultaneous studies on the secretory response of amylase and the neurotransmitter receptors of rat parotid gland, after brief treatment with agonists, showed selective alteration in beta-adrenoceptors with specific change in amylase secretion, suggesting a regulatory role of the receptors in the secretory response. The beta-adrenergic agonist (+/-)-isoprenaline (IPR) stimulated amylase secretion from rat parotid tissues much more than did the same concentration of an alpha-adrenergic or cholinergic agonist. The stimulatory effects of IPR were studied by pre-treating rat parotid tissues with IPR for 10 min and then incubating the tissue in fresh medium for 10 min. Pre-treatment with 10 microM-IPR for 10 min resulted in increased amylase secretion during further incubation with IPR and also in a lower EC50 value of amylase secretion for IPR. This treatment also resulted in selective changes in the number and affinity of beta-adrenoceptors, assessed by measuring binding of [3H]dihydroalprenolol (DHA): the maximal binding sites increased from 286/357 f-mole to mg protein and the IC50 value (the concentration for 50% inhibition of specific [3H]DHA binding) of beta-agonists, not antagonists, decreased significantly. An increase in the period of pre-treatment with IPR to 30 min resulted in a decrease in the maximal binding sites of beta-adrenoceptors and a decrease in amylase secretion during further incubation with IPR. Experiments with other agonists showed that supersensitivity of the secretory response was induced specifically by beta-agonists. Binding studies with [3H]WB-4101 and [3H]quinuclidinyl benzilate showed that alpha-adrenoceptors and muscarinic ACh receptors in rat parotid did not change under the conditions tested. The alteration in beta-adrenoceptors was parallel with a change in amylase secretion after IPR pre-treatment, but not with a change in cyclic AMP content.

High-resolution immunogold cytochemistry indicates that AQP4 is concentrated along the basal membrane of parietal cell in rat stomach

Gastric parietal cells secrete hydrochloric acid in stomach. Because the secreted HCl solution is isotonic with the plasma fluid, it should accompany the water transport across the membranes of parietal cells. Aquaporins (AQPs) are water channel proteins that play the central role in the cellular handling of water in various mammalian tissues. Using immunocytochemistry, we found that AQP4 was expressed only in parietal cells of rat gastric mucosa. Immunogold electron microscopy study further demonstrated that AQP4 was mostly localized at the basal membrane of parietal cells. In the basal membrane, AQP4 was prominently enriched on the portion contacting with the basement membrane surrounding gastric glands. These results suggest that the contact between basement membrane and basal membrane may generate the signal involved in the targeting of AQP4 in gastric parietal cells.

Roles of M2 and M4 Muscarinic Receptors in Regulating Acetylcholine Release From Myenteric Neurons of Mouse Ileum

We investigated the subtype of presynaptic muscarinic receptors associated with inhibition of acetylcholine (ACh) release in the mouse small intestine. We measured endogenous ACh released from longitudinal muscle with myenteric plexus (LMMP) preparations obtained from M1–M5 receptor knockout (KO) mice. Electrical field stimulation (EFS) increased ACh release in all LMMP preparations obtained from M1–M5 receptor single KO mice. The amounts of ACh released in all preparations were equal to that in the wild-type mice. Atropine further increased EFS-induced ACh release in the wild-type mice. Unexpectedly, atropine also increased, to a similar extent, EFS-induced ACh release to the wild-type mice in all M1–M5 receptor single KO mice. In M2 and M4 receptor double KO mice, the amount of EFS-induced ACh release was equivalent to an atropine-evoked level in the wild-type mouse, and further addition of atropine had no effect. M2 receptor immunoreactivity was located in both smooth muscle cells and enteric neurons. M4 receptor immunoreactivity was located in the enteric neurons, being in co-localization with M2 receptor immunoreactivity. These results indicate that both M2 and M4 receptors mediate the muscarinic autoinhibition in ACh release in the LMMP preparation of the mouse ileum, and loss of one of these subtypes can be compensated functionally by a receptor that remained. M1, M3, and M5 receptors do not seem to be involved in this mechanism.

Takayasu arteritis. Treatment and prognosis in a university center in Brazil

The aim of this study was to evaluate the treatment and evolution of TA patients in a University Center in Brazil. This is a retrospective and descriptive study, that included all patients with TAs who attended the out-patient clinic at the Universidade Federal de Sao Palo, between 1993 and 1998. Twenty-four patients were women and 22 where white. The median age at the time of diagnosis was 27 yo. Full arteriography was performed in 28 patients and carotid duplex ultrasound plus computed tomography of aorta was done in two patients. Type I was found in 4, type II-a and type II in one case each, the type IV in 4 cases and the type V in 20 patients. Regarding the treatment only three patients with quiescent disease did not receive any medications. Twenty-seven patients (90%) received prednisone and only ten of these patients achieved disease control. Forth-eight percent of patients who received prednisone showed some side effects. Twelve patients received methotrexate associated to prednisone and 58% of them had a good response. Two patients who did not control disease activity with prednisone plus methotrexate received cyclophosphamide without good results. Some surgical procedure was performed in ten TA patients. Three patients died during the follow-up. This study showed that the majority of TA patients attended at a University Center needed association of prednisone and methotrexate to control disease activity, 30% needed some surgical procedures and that may be a cause of death in a young patient.

Binding interactions of ergot alkaloids with monoaminergic receptors in the brain

The interactions of ergot alkaloids and of other drugs with dopamine (DA) and alpha-adrenergic receptors were investigated. The tested ergot alkaloids inhibit synaptosomal tyrosine hydroxylase activity and reverse the apomorphine-elicited inhibition of synaptosomal tyrosine hydroxylase activity. Thus, ergot alkaloids interact as both agonists and antagonists with the presynaptic DA receptors. Ergot alkaloids also compete effectively for the binding of 3H-DA and 3H-haloperidol to bovine striatal membranes. These results show that these drugs are mixed agonist-antagonists with respect to the postsynaptic DA receptors. To determine the effects of ergot alkaloids and of neuroleptics on the alpha-adrenergic receptors in the CNS, we have measured their effects on the binding of 3H-dihydroergocryptine and 3H-WB-4101 to cerebral cortical membranes. The displacing potencies of the tested ergot alkaloids and of the neuroleptics indicated that they have a high affinity for the alpha-adrenoreceptors in the CNS. The mechanisms underlying the therapeutic efficacy of mixed agonist-antigonists of DA and alpha-adrenergic receptors in Parkinson's disease and in geriatric disorders were considered.

Nitric oxide-mediated inhibitory response of rat proximal colon: independence from changes in membrane potential

1. We studied the relation of nitric oxide-mediated relaxation of smooth muscle to changes in membrane potential of cells in the proximal colon of rats. 2. The resting membrane potential and electrical field stimulation (EFS)-induced junction potentials were recorded from the circular and longitudinal muscle cells. 3. Localized distension with a small balloon caused relaxation of the circular muscle on the anal side of the distended region (descending relaxation). Relaxation of the longitudinal muscle was also induced by EFS. 4. Inhibitory junction potentials (i.j.ps) were recorded from all circular muscle cells tested, but rarely from the longitudinal muscle cells. 5. The i.j.ps were recorded only in the presence of atropine but relaxations of both muscles were induced even in the absence of atropine. 6. Apamin (100 nM) completely abolished the i.j.ps recorded in both circular and longitudinal muscle cells, but had no significant effect on the relaxations of either. 7. In contrast to apamin, Ng nitro-L-arginine (10 microM) inhibited the relaxations of both muscles, but did not affect the i.j.ps. 8. Exogenously added nitric oxide (0.1-10 microM) induced relaxations of both muscles concentration-dependently, but did not affect the membrane potentials at these concentrations. 9. These data strongly suggest that nitric oxide-mediated relaxation of rat proximal colon is not associated with the i.j.ps of the cell membrane.

Decrease in participation of nitric oxide in nonadrenergic, noncholinergic relaxation of rat intestine with age

Participation of nitric oxide in the electrical field stimulation-induced nonadrenergic, noncholinergic (NANC) relaxation in various intestinal regions was studied in 2- to 50-week-old Wistar rats. In the jejunum of 2-week-old rats, the extent of the nitric oxide-mediated component of the relaxation of longitudinal muscle was approximately 60-70%, whereas the component was 40-50% in 4-week-old rats and was absent in 8- and 50-week-old rats. Thus, nitric oxide seems to be the most important mediator at young ages but its significance is lost with age. The same tendency as that in the jejunum was also shown in longitudinal muscle of the ileum, proximal and distal colon, and rectum. The tendency was also shown in the circular muscle of the rectum. Sensitivity of the longitudinal muscle of the jejunum and proximal colon to exogenously added nitric oxide was high in younger rats. Immunoreactive structures for nitric oxide synthase were observed in the circular muscle layer of the rectum. The population of the structures was denser in 4-week-old than that in 50-week-old. The results suggest that NANC relaxation in every region of the intestine at 2-week-old is almost solely mediated by nitric oxide, and its significance as an inhibitory mediator gradually or rapidly decreases with age.