Beta-amyloid neurotoxicity requires fibril formation and is inhibited by congo red

beta-Amyloid (beta A) is normally produced as a nontoxic soluble peptide. In Alzheimer disease, beta A aggregates and accumulates in the brain as inert diffuse plaques or compact plaques associated with neurodegenerative changes. To determine the relationship of neurotoxicity to the physical state of beta A, we created (i) nonamyloidogenic amorphous aggregates of beta A [amorphous beta A (Am-beta A)] analogous to diffuse plaques and (ii) amyloidogenic fibrils of beta A [fibrillar beta A (Fib-beta A)] analogous to compact plaques. In primary rat hippocampal culture, Fib-beta A was neurotoxic, whereas Am-beta A was not toxic. Fib-beta A caused significant loss of synapses in viable neurons, while Am-beta A had no effect on synapse number. The amyloid fibril-binding dye Congo red inhibited Fib-beta A neurotoxicity by inhibiting fibril formation or by binding to preformed fibrils. Congo red also inhibited the pancreatic islet cell toxicity of diabetes-associated amylin, another type of amyloid fibril. These results indicate that beta A neurotoxicity requires fibril formation. These findings and our previous demonstration that amylin fibrils are toxic suggest that a common cytopathic effect of amyloid fibrils may contribute to the pathogenesis of Alzheimer disease and other amyloidoses.

[Effects of pharmacological doses of polyunsaturated fatty acids of the series 3 on the concentration of plasma lipoproteins]

Cardiovascular disease is one of the main causes of death in developed countries. Its incidence may be modified through dietary changes, this being supported by the low incidence of the disease among populations with high intake of fatty fishes. The aim of this work was to study the modifications on plasmatic levels of polyunsaturated fatty acids omega 3 after an additional supply of fish oils and to assess its effect on the metabolism of lipids and lipoproteins. The study was conducted on 8 healthy volunteers, their age ranging between 24 and 37 years. They received, during 30 days and in tablets of 500 mg, 7.5 gr/24 h of fish oil concentrate which supplied 2.5 gr/24 h of fatty acids omega 3. After 12 hours of fasting, blood samples were taken before and after the intake of this concentrate. Methyl esters from fatty acids omega 3 were assessed through gas chromatography; cholesterol, triglycerides, LDL, VLDL, HDLt, HDL2 and HDL3, through several enzymatic techniques; and lipoprotein(a) Lp(a), through ELISA. The statistical analysis was conducted using the Student's method for matched data. After 30 days of supplement, we observed: a significant increase in the plasmatic percentage of fatty acids omega 3 (EPA + DHA) along with a significant decrease of triglycerides, VLDL and HDL3 and a significant increase of HDL2, We did not observe any significant changes in cholesterol, LDL and HDLt. With respect to Lp(a), after one month of dietary supplement, its plasmatic levels did not change. Our results supports the clinical usefulness of the dietary supplementation with fatty acid omega 3 for the management of hypertriglyceridemias.(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreatic islet cell toxicity of amylin associated with type-2 diabetes mellitus

The 37-amino-acid polypeptide amylin is the principal constituent of the amyloid deposits that form in the islets of Langerhans in patients with type-2 diabetes mellitus, but its role in the pathogenesis of this disease is unresolved. In view of the fact that the beta-amyloid protein that forms fibrils in Alzheimer's disease is toxic to neurons, we have investigated whether amylin fibrils could be toxic to pancreatic islet cells. We show here that human amylin is toxic to insulin-producing beta-cells of the adult pancreas of rats and humans. This toxicity is mediated by the fibrillar form of the amylin peptide and requires direct contact of the fibrils with the cell surface. The mechanism of cell death involves RNA and protein synthesis and is characterized by plasma membrane blebbing, chromatin condensation and DNA fragmentation, indicating that amylin induces islet cell apoptosis. These findings indicate that amylin fibril formation in the pancreas may cause islet cell dysfunction and death in type-2 diabetes mellitus.

EFFECTS OF BARIUM CHLORIDE ON ELECTROLYTE TRANSPORT ACROSS ISOLATED COLONS FROM NORMAL AND ALDOSTERONE-TREATED LIZARDS (GALLOTIA GALLOTI)

Addition of BaCl2 to the solution bathing colons of normal lizards did not alter the absorptive Na+ flux, but did reverse the net absorption of Cl- to become net secretion. Cl- secretion resulted from an increase in its serosal- to-mucosal movement and was positively correlated to an increase in short- circuit current. Ba2+-induced short-circuit current was dependent on the presence of both Na+ and Cl- in the serosal medium. Ba2+-induced Cl- secretion could be reversed by serosal amiloride (10–4 mmol l-1). Colons from acutely or chronically aldosterone-treated lizards exhibited a considerably higher short-circuit current, potential difference and net Na+ absorption than did untreated colons. Net Cl- transport was unaltered by acute treatment, but was totally abolished after chronic treatment. BaCl2 rapidly decreased the potential difference, short-circuit current and tissue conductance across colons from aldosterone-treated lizards. Net Na+ transport was markedly inhibited by Ba2+ in both acutely and chronically treated tissues, but barium did not change unidirectional or net Cl- fluxes in these. The present results support the following hypotheses: (1) that BaCl2 inhibits electrogenic Na+ absorption induced by acute or chronic aldosterone treatment and (2) that Ba2+ induces an electrogenic Cl- secretion by stimulating a basolateral Na+-dependent Cl- intake in normal but not in aldosterone-treated colons. This also suggests that aldosterone could exert an antisecretory influence in colonic epithelia.

[Effects of dietary oil (olive/sunflower) on the plasmatic apolipoprotein profile]

FOUNDATIONS: The dietary oil provides a significant portion of the caloric intake in the form of fat, although there is some controversy with respect to the potential positive action of each type of oil. In this study, the effect on the lipo-apoprotein profile of monounsaturated fatty acids (MUFA) provided by olive oil and the polyunsaturated fatty acids (PUFA) provided by girasol oil are compared in a population with high risk of arteriosclerosis, as it is the aged population.

METHODOLOGY

44 aged patients living in the same institution, 21 males and 23 females (age: 79 +/- 6 years), and following two different diets during 3 months, with olive and girasol oils, respectively, participated in the study. Both diets were isocaloric: 2.300 kcal/day, 17% proteins, 33% lipids (30 g/day of oil), and 50% carbohydrates. Plasmatic concentrations of cholesterol (C), triglycerides (TG), c-LDL, c-VLDL, c-HDL2, c-HDL3 and lipoprotein a (Lp[a]), as well as apoproteins A1, B, CII, CIII and E, were assessed. Applied statistics: Student's t test for matched samples.

RESULTS

C and TG plasmatic levels did not changed, whereas levels of c-LDL decreased significantly, as well as levels of polyunsaturated fatty acids (135 +/- 43 and 124 +/- 33 mg/dl., p < 0.009) and levels of apo B (151 +/- 47 and 139 +/- 36 mg/dl., p < 0.009). Levels of c-HDL increased significantly (49 +/- 14 and 52 +/- 16 mg/dl., p < 0.01) as well as levels of apo A1 (190 +/- 32 and 205 +/- 41 mg/dl., p < 0.01). Levels of apo CIII (8.2 +/- 2.8 and 9.9 +/- 3.2 mg/dl., p < 0.008) and apo E (3.2 +/- 1.1 and 3.7 +/- 0.9 mg/dl., p < 0.01) also increased in men. Women did not showed any significant variations in lipoproteins, although apo A1 and apo E increased slightly and apo B decreased, although not significantly, with the polyunsaturated fat. The levels of Lp(a) did not changed.

CONCLUSIONS

In the aged population following a standard diet, without overloads, the PUFAs induced positive changes in the lipoapoprotein profile when compared to a previous diet with MUFA. Those changes were more evident in men than in women.

Amygdala neurons in vitro: neurite growth and effects of estradiol

Dissociated cell cultures from embryonic rat medial amygdala were studied using sequential photography and immunocytochemical staining for cytoskeletal proteins and substance P (sP). Cultures were seeded with cells taken from fetuses grouped by sex; experimental cultures were raised in medium containing 17-beta-estradiol (E2). Forty-eight hours after plating a few neurons begin to define their morphological polarity by the differentiation of an axon-like process; at 5 days in vitro (DIV) almost all neurons had developed an axon. Tapering, daughter branch ratio and branch power coefficient coincided with identification of dendrites which could be confirmed by retrospective analysis of immunocytochemically stained cultures: at 5 DIV MAP-2 was restricted to dendrites whereas Tau immunoreactivity was differentially localized with a clear predominance in the axon. At 21 DIV neuronal shape parameters were strikingly like those of amygdaloid neurons in vivo. It was demonstrated in living neurons that E2 increased total dendritic length and that this is due to increased ramification of third or higher order dendritic segments whose individual lengths are not different from controls. Densitometric measurement of MAP-2 stained neurons showed a highly significant increase of immunoreactive material in cells grown in the presence of E2; readings for alpha-tubulin were not different between controls and E2 treated cultures. The effect of E2 on dendritic length was just as manifest in sP-positive as in sP-negative neurons. No sexual differences in morphological parameters, growth characteristics or effects of E2 were found in neurons taken from female fetuses versus neurons from male fetuses. The significance of these results for the generation of sexual differences in the amygdala in vivo is discussed and contrasted with reported results on the effects of E2 in cultures of different neural regions.

Ultrastructural observations on blood vessels surrounding normal and regenerating spinal cord in newt

The ultrastructural analysis of capillaries surrounding normal and regenerating caudal spinal cords of two species of newt (Triturus vulgaris and T. cristatus) is reported. Around normal spinal cords, capillaries were generally continuous. Surrounding the regenerating spinal cords the various capillaries of the regenerating blastema appeared discontinuous with small or broad gaps along the capillary wall. This was seen even after two months of tail regeneration when the spinal cord was similar to the normal and many axons were myelinating. These morphological findings suggest that during tail regeneration in newts the blood-brain barrier is not very effective. Also extravasating mature and immature blood cells were observed inside regenerating capillaries. Therefore growing capillaries can exchange metabolites and, possibly, growth factors with the nervous tissue and the other regenerating tissues.

Plasmatic fibronectin in malignancies

Plasmatic fibronectin has been studied in tumor patients on the basis of the role that unspecific opsonin may play in tumor growth and spreading. Alterations in fibronectin levels might be used as a biological marker and our purpose has been to evaluate the significance of this test in the biological diagnosis of cancer. When comparing the levels found in the control group (22.86 +/- 1.40 mg/dl) and in tumor patients (23.80 +/- 1.90 mg/dl), we observed no difference in the overall group. However, in relation to the localization of tumors, a significant increase was found in breast cancer (31.83 +/- 3.83 mg/dl) and a significant decrease in squamous cell carcinoma of the head and neck (9.56 +/- 1.68 mg/dl). These results suggest that plasmatic fibronectin could be useful as a biomarker in some types of tumors. Our conclusion was confirmed by analysis of ROC curves related to every one of the studied tumors.

Time lapse study of neurite growth in hypothalamic dissociated neurons in culture: sex differences and estrogen effects

Cultures of dissociated hypothalamic cells taken from rat fetuses of 19 days of gestation were studied using time-lapse recording and sequential microphotography from 1 to 5 days in vitro (DIV) and at 7 and 21 DIV. Cultures were seeded with cells taken from fetuses grouped by sex or sexually mixed; experimental cultures were raised in medium containing 17-beta-estradiol 100 nM (E2). Cells were plated on poly-D-lysine-coated coverslips at a culture density of approximately 4,000 cells/cm2. Immunocytochemistry of cell cultures was performed using a Tau monoclonal antibody (clone Tau-1 PC1C6) and a monoclonal antibody against MAP-2 (clone AP-20). Cells started to produce lamellipodia and neuritic processes approximately 4 hr after plating. Forty-eight hours later a few neurons had defined their morphological polarity by the differentiation of an axon-like process that grows faster than the others; at 5 DIV almost all neurons had defined their axons. At this time, monoclonal antibody against MAP-2 clearly stained soma and dendrites, but not axons. Tau immunoreactivity (lots CCA101 and CCA101N from Boeringher Mannheim) was differentially distributed, with a clear predominance in axon and soma. Results on the morphometric analysis of control and E2 treated neurons provide direct evidence for the existence of sex related differences in the neurite outgrowth response of hypothalamic neurons, since cultured neurons taken from female fetuses differentiated axons later and had fewer primary neurites and shorter dendrites than neurons taken from male fetuses or sexually mixed cultures. Also, it was demonstrated in living neurons that E2 effectively enhances outgrowth and elongation in axons. The frequency distribution curves of axonal length for control and E2 treated cultures was unimodal, suggesting that the effect of E2 was a uniform increase in the axonal length of all neurons. The structural differences between neurons from both sexes and the changes induced by E2 may contribute to explain the differences in brain function found between the sexes.

Methodological variables in the assessment of beta amyloid neurotoxicity

Cell culture systems for evaluating the biological effects of the beta-amyloid protein are potentially important tools in the study of the pathogenesis of Alzheimer's disease. In this report, methodological considerations in the assessment of beta-amyloid neurotoxicity are discussed. Chronic incubation of beta 1-40 in primary human cortical cultures results in progressive neuronal degeneration. The neurodegenerative process occurs in association with localized deposition of beta-amyloid on the neuronal soma ultimately resulting in the formation of compact beta-amyloid deposits. A beta 1-40 preparation from another laboratory was tested that did not form neuronal beta-amyloid deposits and was not neurotoxic. Thus, the conformational state of the beta 1-40 peptide leading to the formation of neuronal amyloid deposits is an important determinant of neurotoxicity. Variables in peptide preparation that influence this property may account for variation in neurotoxic potency.

[Beta-thromboglobulin levels and atherosclerosis. Its relationship with the presence of risk factors]

In order to evaluate whether plasma beta-thromboglobulin (as a marker of the degree of platelet function) in patients presenting clinically evident atherosclerosis is related to the presence or absence of different risk factors (smoking habit, arterial hypertension, hypercholesterolemia, diabetes, hypertriglyceridemia, obesity, hyperuricemia, alcoholism), 40 patients have been studied in whom mean beta-thromboglobulin levels was 54 +/- 25.56 ng/ml, which is very superior to levels considered normal. However, the presence of one or more risk factors did not lead to significant variations in b-thromboglobulin concentrations, and no differences were found either when each risk factor was considered separately. The positive correlation (r = 0.98; p less than 0.01) between beta-thromboglobulin and apo B levels is highlighted. The results suggest that platelet hyperfunction seems to be due to a greater extent to the atherosclerotic process rather than to the existence of a particular risk factor.

[Ceruloplasmin levels in patients with chronic obstructive bronchopneumopathy]

The seric levels of ceruloplasmin in a group of 20 patients suffering of chronic obstructive lung disease were studied. Levels in this group of patients (51.42 +/- 11.15 mg/dl) (p less than 0.005) were significantly higher than those of the control group (36.59 +/- 13.37 mg/dl). There was no correlation between ceruloplasmin levels and PaO2, PaCO2, SaO2, HCO3- measurements. Results show a possible oxidation reaction; owing to the fact that ceruloplasmin is a general oxidase which, combined with an antioxidant stimulus of patients with chronic respiratory insufficiency, can produce this reaction.

[Results of the functional tests using calcitonin in patients with chronic diffuse hepatopathy]

A group of ten patients suffering cirrhosis who were treated with 100 U/l of calcitonin was studied with the aim of knowing whether in patients with cirrhosis the calcitonin is able to provoke the usual characteristic biologic modifications on the basis of the knowledge of their hormonal high levels accompanied of oesteopenia. Regarding their baseline determinations, no statistically significant modifications have been observed in calcium, phosphorous, alkaline phosphatase or its thermostable and thermolabile fractions, magnesium, uric acid and creatinine plasma concentrations respectively. This absence of a biological response to calcitonin could be due either to a numeric or functional damage of the hormone receptors or a diminished biodisponibility, although there are facts suggesting a lesser hormone biopotenciality in these patients.

Rat blood and brain amino acid pattern in short term experimental diabetes

Some serum and brain amino acid variations occurring in animals with short term streptozotocin-diabetes (24 h) are studied in this work. Diabetic animals showed an increase in serum of the three branched-chain amino acids as well as an increase in free tryptophan, besides a decrease in total serum tryptophan and in the tryptophan/competitor amino acids ratio. In brain, the three branched-chain amino acids increased, but there were no variation in whole brain tryptophan. Nevertheless, by studying levels of tryptophan in different brain regions, an increase in medulla-pons was recorded. This circumstance could be explained by the increase in free serum tryptophan levels, in agreement with several authors who assign this reason for brain tryptophan.

Electrical properties and fluxes of Na+ and Cl- across lizard intestine

Electrical parameters and unidirectional Na+ and Cl- fluxes were determined in vitro across the duodenum, ileum and colon of lizard (Gallotia galloti). Electrical potential difference (PD) and short circuit current (Isc) were low in the three segments studied, whilst tissue conductance (Gt) was high. A net active transport of Na+ and Cl- was observed in the three segments. Net Na+ absorption was higher across duodenum and ileum than across the colon, while net Cl- absorption was similar in duodenum, ileum and colon. Ouabain virtually abolished Isc, PD and net Na+ and Cl- fluxes in all the segments. Amiloride abolished net Cl- flux in duodenum, ileum and colon, whereas net Na+ flux was abolished in colon but decreased in duodenum and ileum. PD and Isc were not affected by the presence of the diuretic.

Verapamil injections in the peripeduncular nucleus suppress multiunit evoked activity and sexual receptivity in female rats

Using a combination of injection cannula and recording electrode, the effect of 1 microliter of 3 mM verapamil upon the multiunit responses evoked in the peripeduncular nucleus (PPN) by electric stimuli applied to the pudendal nerves in urethane anesthetized proestrous female rats was studied in 9 experiments. It was observed that in 6 cases responses were suppressed after the injection and in 2 other cases there was a marked decrease, whereas no change was observed in 1 case. Similar injections of vehicle (saline) produced no change (7 rats) or small and short lasting depression of evoked activity (4 rats). Similar injections of verapamil applied to a region of the mesencephalic reticular formation caudal to the PPN, presumably containing fibers that carry evoked activity towards the PPN, had no effect on evoked multiunit activity in the PPN. Injection of 2% Xylocaine in the same site in the same animal eliminated the evoked responses. These experiments support our hypothesis that verapamil suppressed evoked responses in the PPN blocking Ca++-dependent release of neurotransmitter at local synapsis, without interfering with fiber conduction of neural activity. Based on this assumption we used identical injections to test the hypothesis that activation of neurons in the PPN is necessary for the performance of lordotic behavior in ovariectomized rats primed with estradiol benzoate. Guide cannulae aimed at the PPN were implanted in castrated females which were then primed with enough estradiol benzoate to induce sexual receptivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological changes in serum antiproteases as related to tumor progression

The two major antiproteases (alpha-1-antitrypsin and alpha-2-macroglobulin) were studied in the serum of cancer patients (273 and 103 subjects, respectively) and in a control group. In cancer patients, the values were stratified by clinical stage (local, loco-regional and metastatic disease). Serum alpha-1-antitrypsin was different in normal people (341 +/- 110.7 mg/dl) than in every cancer group (p less than 0.0005). The behavior of alpha-2-macroglobulin was similar, with significant differences (p less than 0.0005) between normal people (317.6 +/- 105.4 mg/dl) and the cancer groups. Serum alpha-1-antitrypsin was different in local, loco-regional and metastatic disease; however, alpha-2-macroglobulin did not show these differences. In metastatic disease, sensitivity was 96.66% for alpha-1-antitrypsin and 94.79% for alpha-2-macroglobulin.

The role of aldosterone in water and electrolyte transport across the colonic epithelium of the lizard, Gallotia galloti

1. The effects of D-aldosterone on the electrical properties and ionic transport have been analysed (in vitro) in the colonic epithelium of the lizard, Gallotia galloti. 2. The injection of 30 g of D-aldosterone induced a significant rise of plasma aldosterone concentration, sustained for 4 hr after administration. 3. Intraperitoneal injections of D-aldosterone caused a slight reduction of transmural potential difference (PD) and short-circuit current (Isc). 4. Net absorption of Na+ across the colon from aldosterone-treated lizards did not increase when compared to colon from normal lizards. Cl- absorption was increased in treated lizards. 5. Addition of mucosal barium to treated tissues brought about a sustained increase of PD and Isc. 6. The absorption of fluid in normal lizards was reversed to fluid secretion in treated lizards. 7. The effects of D-aldosterone on lizard colon are compared with those reported for the colon of mammals and birds.

Significance of the changes in plasma amino-acid levels in meningococcal infection

A series of patients with meningococcal infections have been studied and divided in two groups: Group I patients with meningococcal sepsis and group II, those with meningococcal meningitis. Patients in group I presented with more severe encephalopathy, shock, DIC and acute systemic complications. Both groups showed a marked hypoaminoacidemia compared with normal controls (other than for the sulfur containing amino acids and phenylalanine). The concentration of aromatic and basic amino acids, the phenylalanine/tyrosine ratio, the transaminase levels and the negative nitrogen balance were higher in group I patients. The ratio of branched chain to aromatic amino acids was lower in group I. All these differences were statistically significant. The close association between the metabolic derangements and clinical manifestations may help in the understanding of several physiopathological aspects of meningococcal infections.

Intestinal glucose and galactose transport in the cultured gilthead bream (Sparus aurata)

1. Electrical parameters and transepithelial glucose and galactose transport were determined in vitro across anterior and posterior intestine of the culture fish Sparus aurata. 2. Electrical potential difference (PD) and short-circuit current (Isc) were serosa-positive in anterior intestine, while they were serosa-negative or near zero in posterior intestine. 3. Tissue conductance (Gt) was higher in posterior than in anterior intestine. In both parts it was decreased when the Na ion was omitted in mucosal and serosal reservoirs. 4. Addition of glucose or galactose to the mucosal side of intestine caused an increase in PD and Isc in posterior intestine but did not significantly change PD and Isc in anterior intestine. 5. Isotopic flux of glucose and galactose measurements in short-circuit conditions showed a net active glucose and galactose absorption in posterior intestine, while in anterior intestine active transport of glucose or galactose was not observed. 6. The net transport of glucose and galactose in posterior intestine was decreased to zero in the absence of Na in mucosal and serosal reservoirs or in the presence of ouabain (1 mM) in serosal solution.

Effect of theophylline on ion transport in the lizard colon

1. The effect of theophylline on ion transport was examined using an in vitro short-circuited preparation of lizard colon. 2. Theophylline increased short circuit current (Isc) and transmural potential difference (PD). This increase caused by theophylline was accompanied by a small increase in transmural conductance (Gt). 3. Theophylline did not inhibit the absorption of Na+ but reversed Cl- absorption to secretion. This latter effect was due to an increase of the serosal-to-mucosal flux of Cl-. 4. Ion substitution experiments revealed that the effect of theophylline was Na+- and HCO3(-)-dependent and that these ions were required in the bathing solution. 5. These results with lizard colon are compared with those reported for mammalian colon and the mechanism of theophylline-induced Cl- secretion in these epithelia is discussed.

Delayed repair of an acquired posterior septal defect through a right atrial approach

A patient with chronic postinfarction ventricular septal defect located posteriorly is described. The right atrial approach is suggested for these defects and the operative differences between chronic and acute defects are discussed.

Transport of galactose and sodium across lizard duodenum

Electrical parameters and transepithelial Na+ and galactose transport were determined in vitro across isolated duodenum of Lacerta galloti lizard. Electrical potential difference (PD) and short-circuit current (Isc) were dependent on the presence of Na+ in the bathing solutions. PD and Isc were affected by addition of galactose to the mucosal solution. Isotopic flux of Na+ measurements across short-circuited duodenum showed a net active Na+ absorption. The net flux of Na+ (JNa+net) accounted for the observed Isc. Both (JNa+net) and Isc were increased by the addition of galactose 5 mM to the mucosal solution. Isotopic flux galactose measurements in open-circuit conditions showed a net active galactose absorption. The net transport of galactose was decreased to zero in the absence of Na+ in mucosal and serosal reservoirs. Galactose has been used to induce changes in short-circuit current (delta Isc) across intestine. delta Isc was a hyperbolic function of galactose concentration characterized by the parameters Vmax (maximum change in delta Isc) and Km (concentration needed to attain a velocity equal to half the Vmax).

Electrical properties of a Na+-dependent phenylalanine transport in lizard (Lacerta galloti) duodenum

The unidirectional transepithelial fluxes of L-phenylalanine across lizard duodenum were determined in flux chambers. Phenylalanine was preferentially transferred from the mucosal to the serosal fluid. This transport was accompanied by an accumulation of substrate from the mucosal medium into the tissue to a similar level and against a concentration gradient. There was no net movement of phenylalanine when the sodium was substituted by choline. The influx of L-phenylalanine into the epithelial cells of lizard duodenum was examined by incubating slices of intestine in radioactively-labelled solutions of the substrate for 2 min. The steady-state uptake was assessed after similar incubations lasting 45 min. Phenylalanine influx obeys the Michaelis-Menten equation with a Km of 5.1 and is dependent on the presence of sodium ions in the incubation medium. Phenylalanine has been used to induce changes in short-circuit current (delta Isc) across intestine. delta Isc was a hyperbolic function of amino acid concentration characterized by the parameters Jm (maximum change in delta Isc) and Km (concentration needed to attain an delta Isc equal to half the Jm). delta Isc determined Km constants showed good agreement with values obtained from direct measurements of phenylalanine uptake into tissue.

Bioelectric parameters and sodium and chloride fluxes across the intestine of Blennius parvicornis

Simultaneous measurements of the electric potential difference and the short-circuit current intensity were taken, as well as measurements of unidirectional fluxes of sodium and chloride in the posterior intestine of Blennius parvicornis fish. On incubating the tissue in standard Ringer solution, a potential difference of--0.9 mV, a mean net flux of sodium of 2.49 mu Eq/h x cm2 were obtained. In the absence of sodium (choline as substitute), the net chloride flux and the Isc were completely blocked. In the absence of chloride (isocyanate as substitute) the net sodium flux and the Isc were equally blocked. Ouabain lessened the sodium and chloride fluxes in the mucosa-serosa direction to the point of nulling the net fluxes of both ions. The values of the bioelectric parameters were also blocked in the presence of this inhibitor. Acetazolamide did not significantly affect the values of either the unidirectional fluxes or the net fluxes of sodium and chloride. Nor did it affect the values of the bioelectric parameters. A mechanism for the absorption of sodium and chloride is proposed in which these ions enter the cell in a coupled form and in 1:1 proportion, the transport being independent of the bicarbonate ion.

Transmural potential differences and short-circuit current intensity in the posterior intestine of Blennius parvicornis

Simultaneous measurements of the transmural potential difference (PD) and the short-circuit current intensity (Isc) in the posterior intestine of the fish Blennius parvicornis were made in normal Ringer and in solutions of different ionic composition. The ouabain effects on these two parameters were also tested in normal Ringer solution. The absence of K+ from the Ringer solution on both the mucosal and serosal sides has no apparent effect on the PD and Isc within the first 15 min, but it makes them null after 30 min. When Na+ is substituted in both compartments, using Tris as substitute, a serosal negativity increase is initially observed, but it gradually decreases to zero after 30 min of experimentation. Similarly the PD and Isc drop to zero in the absence of Cl- (sulfate as substitute). Ouabain diminishes the serosa negative potential difference to zero after 30 min presenting a lineal relation to the Isc. A likely transport mechanism for Cl- dependent on the Na+ - K+ pump, is discussed.