The effect of phenylalanine on intracellular pH and sodium activity in proximal convoluted tubule cells of the frog kidney

The present study was performed to test the influence of sodium coupled transport of neutral substrates on intracellular pH and sodium activity in proximal tubules of the amphibian kidney. To this end, kidneys of rana esculenta have been isolated and perfused both through the portal vein (peritubular capillaries) and the aorta (luminal perfusate). The potential difference across the peritubular membrane of proximal tubule cells has been reduced with conventional (PDpt) as well as with sodium (PDna) and hydrogen ion (PDh) selective microelectrodes continuously before, during, and after the luminal application of 10 mmol/l phenylalanine, replacing 10 mmol/l raffinose. PDh and PDna allowed the calculation of intracellular pH (pHi) and sodium activity (Nai), respectively. In the absence of phenylalanine in the tubule lumen, PDpt approximates -57.5 +/- 2.3 mV (n = 27), pHi 7.73 +/- 0.04 (n = 14, extracellular pH 7.77), and Nai 13.3 +/- 0.9 mmol/l (n = 13, extracellular sodium activity 74 mmol/l). Within 1 min the luminal application of phenylalanine leads to a depolarisation of PDpt by +32 +/- 2 mV, as well as an increase of pHi by 0.24 +/- 0.04 and of Nai by 5.2 +/- 1.0 mmol/l. At 8 min from luminal application of phenylalanine, Nai plateaus 5 +/- 1 mmol/l above control value, PDpt increases again to a value of +12 +/- 2 mV below and pHi decreases to a value 0.04 +/- 0.07 above their respective control values. All changes are fully reversed after removal of phenylalanine from the tubule lumen.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of topical adenosine deaminase treatment on the functional hyperemic and hypoxic responses of cerebrocortical microcirculation

The purpose of this study was to investigate the possible importance of adenosine in cerebrocortical vasodilatation accompanying brain activation (epileptic seizures and direct electrical stimulation) and hypoxia (arterial hypoxia and cyanide poisoning of the brain cortex). In chloralose-anesthetized cats a circumscribed area of the brain cortex was treated with adenosine deaminase (Type III; Sigma), which potently deaminates adenosine to the nonvasoactive inosine. Cerebrocortical vascular volume and fluorescence of reduced nicotinamide adenine dinucleotide were measured in vivo by surface fluororeflectometry. The responses of small pial and intracortical vessels to brain activation and hypoxia were studied in brain cortices superfused with artificial (mock) CSF and 5 U/ml adenosine deaminase. It was found that superficially applied adenosine deaminase readily diffuses onto the brain cortex. Prolonged pretreatment of the brain cortices with 0.025 U/ml adenosine deaminase eliminated almost completely the vasodilative effect of 10(-7) mol/ml adenosine. The inhibitory effect of the enzyme on adenosine-induced cortical vasodilatation was specific, because 5 U/ml adenosine deaminase did not attenuate the vasodilative potency of 10(-8) mol/ml 2-chloroadenosine. Adenosine deaminase (5 U/ml) pretreatment of the brain cortices did not diminish the cerebrocortical vascular volume, which increased with arterial hypoxia, topical cyanide poisoning, and direct electrical stimulation. However, it slightly decreased the vasodilative effect of epileptic seizures. On the basis of these results, it seems very unlikely that adenosine is a critical factor in the control of cerebrovascular tone during arterial hypoxia and brain activation.

Possible role of nickel ions in the pathogenesis of ischemic coronary vasoconstriction in the dog heart

To test the hypothesis that nickel ions released from the ischemic dog myocardium [18] play a role in the pathogenesis of ischemic coronary vasoconstriction, the present experiments on the in situ heart of the anesthetized open-chest dog were designed to analyze coronary vascular action of intravenous (i.v.) and intracoronary (i.c.) injection of exogenous NiCl2 under the influence of ischemia, arterial hypoxemia and adenosine. The experimental results showed that (1) exogenous NiCl2 induced coronary vasoconstriction by a direct action on coronary vessels in low doses (0.02 mg X kg-1 i.v. bolus injection, or 0.04 mg X min-1 X kg-1 i.c. infusion) comparable to the Ni amount released endogenously, (2) NiCl2 significantly inhibited postocclusion reactive hyperemia and coronary vasorelaxation in response to arterial hypoxemia or intracoronary infusion of adenosine, (3) NiCl2 is capable of inducing coronary vasoconstriction when the coronary arteries are dilated by low flow ischemia, arterial hypoxemia and adenosine infusion, and (4) the Ni-sensitivity of coronary arteries increases significantly under these conditions. A hypothetical model is proposed summarizing the possible positive feedback loops triggered by endogenous Ni-release, which may cause coronary vasoconstriction in the ischemic dog myocardium.

Effect of the organic calcium antagonist D-600 on cerebrocortical vascular and redox responses evoked by adenosine, anoxia, and epilepsy

The purpose of this study was to investigate the role of calcium ions in cerebrocortical vasodilatation and oxidized and reduced nicotinamide adenine dinucleotide (NAD/NADH) redox responses evoked by adenosine, anoxia, and epileptic seizures. The brain cortex of chloralose-anaesthetized cats was treated locally with gallopamil-hydrochloride (D-600) and verapamil (Isoptin®). These organic calcium antagonists decrease the inward movement of calcium ions into vascular smooth muscle cells. Cerebrocortical vascular volume (CVV) and NADH fluorescence were measured in vivo by fluororeflectometry. Adenosine and calcium antagonists were dissolved in artificial cerebrospinal fluid (mock CSF) and applied topically to the brain cortex by superfusion. Adenosine (10−8to 10−3M) resulted in concentration-dependent increases in CVV. The NAD/NADH redox state was not altered below adenosine concentrations of 10−5M. However, in the concentration range of 10−5to 10−3M, significant NAD reduction was obtained. Both calcium antagonists increased CVV markedly, but did not bring about significant changes in NAD/NADH ratio and local electrical activity of the exposed brain cortex. D-600 (2 × 10−6M) increased CVV as much as did 10−4M adenosine, but it failed to diminish the vascular and metabolic effects of the adenosine. D-600 (2 × 10−4M) resulted in an increase in CVV approximately 2.5 times greater than that caused by 10−4M adenosine alone. However, the adenosine-induced CVV response was inhibited by only about 70%, compared with the control response. After pretreating the brain cortex with 2 × 10−3M D-600, adenosine had no effects on CVV and NAD/NADH redox state; the NAD reduction accompanying anoxia and epileptic seizures was considerably diminished. These results suggest that the inhibition of transmembrane calcium influx could have a minor role in the vasodilatatory mechanism of adenosine. Since the vascular effect of adenosine vanished only at very high concentration of D-600, which might also inhibit the release of calcium from intracellular binding sites, it is presumed that adenosine dilates the cerebrocortical vessels by interacting with intracellular calcium-sequestrating mechanisms. Furthermore, since adenosine had a marked NAD reducing effect and since it is well known that it increases the activity of adenylate cyclase and phosphorylase enzymes, accumulation of 3′,5′-cyclic adenosine monophosphate (cAMP) and substrate mobilization might be involved also in the vasodilatatory mechanism of adenosine. Our results concerning the inhibitory effect of D-600 on epilepsy- and anoxia-induced cerebrocortical NAD reduction unambiguously demonstrate the significance of calcium fluxes in glycogen and glucose metabolism under these conditions.

The influence of maternal immunoglobulin-G-antibodies on indirect haemagglutination in newborns

High antibody titers against Escherichia coli were found in 100 randomly selected pregnant women by means of indirect haemagglutination (IHA). After birth, sera from the umbilical vein of the newborns were also tested. It was found that the indirect haemagglutination titers of the children were strongly influenced by the IgG which had been transferred via the placenta. Twenty-two sera of newborns showed an increased IHA-titer against E. coli, but only seven children displayed specific IgM antibodies, determined by indirect immunofluorescence. After chromatographic separation of the sera into IgG and IgM fractions, it was demonstrated that isolated antibodies of the IgG type alone can produce increased IHA titers. The assumption that the indirect haemagglutination is determined almost exclusively by antibodies of the IgG type is unfounded. Therefore, indirect haemagglutination is not suitable as a screening-test for newborns.

Canaline carbamoyltransferase in human liver as part of a metabolic cycle in which guanidino compounds are formed

This and previous papers examine the reasons for the relationship between the concentrations of guanidino-succinate and guanidinoacetate in human urine. With the demonstration here that extracts of human liver-tissue can mediate ureidohomoserine formation from canaline [(2-amino-4-aminooxy)-butyric acid] and carbamoyl phosphate, all steps in a cycle proposed for the production of guanidinoacetate and guanidinosuccinate have been documented. This includes synthesis of canavaninosuccinate from aspartate and ureidohomoserine, reductive cleavage of canavaninosuccinate to form guanidinosuccinate and homoserine, or, alternatively, lytic action on canavaninosuccinate to form fumarate and canavanine, and transamidination to glycine to form guanidinoacetate, regenerating the canaline. We propose that canaline originates from aspartate, but the precise mechanism by which canaline is formed needs to be elucidated.

Canaline carbamoyltransferase in human liver as part of a metabolic cycle in which guanidino compounds are formed

This and previous papers examine the reasons for the relationship between the concentrations of guanidino-succinate and guanidinoacetate in human urine. With the demonstration here that extracts of human liver-tissue can mediate ureidohomoserine formation from canaline [(2-amino-4-aminooxy)-butyric acid] and carbamoyl phosphate, all steps in a cycle proposed for the production of guanidinoacetate and guanidinosuccinate have been documented. This includes synthesis of canavaninosuccinate from aspartate and ureidohomoserine, reductive cleavage of canavaninosuccinate to form guanidinosuccinate and homoserine, or, alternatively, lytic action on canavaninosuccinate to form fumarate and canavanine, and transamidination to glycine to form guanidinoacetate, regenerating the canaline. We propose that canaline originates from aspartate, but the precise mechanism by which canaline is formed needs to be elucidated.

Osteopathy due to methotrexate

Two children with ALL receiving long-term therapy with methotrexate (50 mg/week i.v.) developed severe osteoporosis accompanied by swelling of the joints, gait disturbances and fractures after minimal trauma. Bone scans 85Sr disclosed a decreased input and increased turnover of calcium especially in the most used bones. The data of the calcium phosphorus metabolism are within the normal range. The minimal changes in the biopsy material of the iliac crest may be due to little mechanical use so that this part of the skeleton is not much affected by the osteoporosis. Since the controls receiving the same therapy did not have signs of such severe osteoporosis it is assumed that an additional, till unknown factor may play an additional role in this kind of methotrexate side effect.

Hepatic synthesis of canavaninosuccinate from ureidohomoserine and aspartate, and its conversion to guanidinosuccinate

This study continues the exploration of the mechanism for the formation of guanidinoacetate and guanidinosuccinate in the human [Clin. Chem. 21, 235 (1975)]. In this report we describe the formation of canavaninosuccinate from ureidohomoserine and aspartate by a human or bovine liver extract that had high argininosuccinate synthetase (EC 6.3.4.5) activity, and the subsequent formation of guanidinosuccinate by reductive cleavage. In the presence of ATP the optimum pH for the synthetic reaction is 8.4. This reaction can be carried out in either a tris(hydroxymethyl)aminomethane or borate buffer. Subsequent addition of dithiothreitol in the presence of Fe2+ resulted in the cleavage of some of the synthesized canavaninosuccinate to form guanidinosuccinate and homoserine. Synthesis of canavaninosuccinate was strongly inhibited by added argininosuccinate, less so by canavaninosuccinate, arginine, canavanine, glycine, or 2,3-dimercaptopropanol. The Km values for the substrates of the synthetic reaction are 3.6 X 10(-4) mol/liter for aspartate, 1.6 X 10(-3) mol/liter for ureidohomoserine, and 2.92 X 10(-5) mol/liter for ATP. These values are higher than those obtained when the synthesis of argininosuccinate was studied, except for ATP, which yielded a lower value. All of the reactions in the proposed mechanism have now been demonstrated except for the synthesis of canaline from aspartate.

Evidence supporting a proposed mechanism explaining the inverse relationship between guanidinoacetate and guanidinosuccinate in human urine

A proposed mechanism [Clin. Chem. 19, 668 (1973)] for the inverse relationship between guanidinoacetate (I) and guanidinosuccinate (II) in human urine is explored. The mechanism proposes that canavaninosuccinate (III) may be reduced to form homoserine and II or, alternatively, that the III may be acted upon by a lyase to form canavanine and fumarate. The canavanine would then proceed to transamidinate to glycine to form I. This study demonstrates for the first time that lyase activity for converting III to canavanine and fumarate exists in human liver and kidney extracts. Transamidination from canavanine to glycine to form I is also readily accomplished with human tissue. Reductive cleavage of III to II and homoserine has been demonstrated before [Clin. Chem. 15, 397 (1969)]. The optimum pH for the lyase reaction is 6.5, for the reductive cleavage it is 8.7. In following the course of the lyase reaction, we developed a technique whereby the fumarate formed was hydrated with fumarase (EC 4.2.1.2) and then dehydrogenated with malate dehydrogenase (EC 1.1.1.37). The changes in absorbance of NADH formed in the reaction were then measured and used to determine the amount of fumarate formed, as a measure of lyase activity. Canavanino-succinate lyase activity follows pseudo-first-order reaction kinetics. The Michaelis constant of this lyase was 6.16 X 10-4 mol/liter, for argininosuccinate lyase 9.74 X 10-4 mol/liter. These data suggest that the binding affinity for III to the enzyme is greater than that for argininosuccinate. Glycine added to the reaction acts as an activator, probably because it removes the canavanine from the reaction mixture. On the other hand, arginine acts as an inhibitor of III-lyase. Other substances tested, such as canavanine, fumarate, and argininosuccinate had no effect on the reaction kinetics.