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Biomedical subjects

J L Costa

Publications and source records attributed to J L Costa.

At least 55 records · Page 3Linked to original sources
PubMed1983

Reserpine as an uncoupler of oxidative phosphorylation and the relevance to its psychoactive properties.

Many drugs differing widely in chemical structure uncouple mitochondrial oxidative phosphorylation in vitro. This observation has led to the hypothesis that in vivo uncoupling is the basis of their pharmacological activity. Serpasil, a parenteral preparation of reserpine, recently has been shown to uncouple oxidative phosphorylation in vervet monkey kidney mitochondria. Although the drug exhibits some properties of a "classical" uncoupler, our studies show that it has a dual effect on energy conservation. Reserpine released respiratory control in rat liver mitochondria only when dissolved in organic solvents (as in Serpasil) or when deprotonated. Reserpine also released the oligomycin-induced respiratory control in beef heart submitochondrial particles, and inhibited energized uptake of Ca2- by rat liver mitochondria. Reserpine had a dual effect on mitochondrial ATPase: It (a) enhanced ATP hydrolysis by intact liver mitochondria, and (b) inhibited ATP hydrolysis by submitochondrial particles of beef heart. On a molar basis, reserpine was less effective than carbonyl cyanide 3-chlorophenylhydrazone in all bioenergetic reactions examined. Homogenates and mitochondria isolated from brain and liver of rats stuporous from intraperitoneally injections of Serpasil exhibited no detectable abnormalities in respiratory states and responded to known uncouplers in the expected manner. There was no evidence of in vivo uncoupling of oxidative phosphorylation as a basis of the pharmacological activity of reserpine, although interference with energy transfer may be involved in toxic manifestations of the drug. The results indicate the need for caution in interpreting the action of drugs formulated in complex pharmaceutical preparations and based solely on in vitro experiments.

2,4-Dinitrophenol↗
PubMed1983

Direct observation of 6-fluorodopamine in guinea pig nerve microsacs by 19F NMR.

19F nuclear magnetic resonance (NMR) has been used to examine the disposition of ring-fluorinated dopamine and norepinephrine in microsacs prepared from striata of guinea pig brains. Following incubation with a 10(-4)M initial concentration of 6-fluorodopamine (6F-DA), intact micmicrosacs at 4 degrees C gave a 19F NMR spectrum in which the 6F-DA present was sufficiently mobile to be visible. Intra-vesicular 6F-DA in striatal nerve terminals thus appears to exist in an environment resembling that in chromaffin vesicles but different from that prevailing inside the amine storage vesicles of platelets. Our data also suggest that the study of fluorinated compounds by 19F NMR can be used to expand our understanding of processes related to amine uptake, metabolism, and storage in nerves.

Animals↗
PubMed1983

X-537A ionophore-mediated calcium transport and calcium phosphate formation in Pressman cells.

The present study examined precipitate development induced in phosphate solutions by the ionophoric translocation of Ca2+ across a bulk organic solvent barrier. Experiments were conducted at pH 7.4 and 25 or 37 degrees in a three-compartment Pressman cell. The aqueous reaction (0, 2.2 or 22 mM phosphate, 100 mM K+) and donor (1.3 or 13 mM Ca2+, 0.8 mM Mg2+, 100 mM Na+) compartments were separated by a CHCl3 compartment rendered permeable to cations by the addition of the carboxylic ionophore X-537A (2 or 20 mM). The resultant cation movements increased Ca2+, Mg2+, and Na+ concentrations in the reaction compartment at the expense of K+ loss to the donor compartment. The magnitude of the K+ counterflow and the efficiency of the ionophore-mediated Ca2+ in equilibrium 2K+ exchange reaction resulted in appreciable Ca2+ overshoots in the reaction compartment. In the absence of phosphate, Ca2+ increases exceeded donor levels by several-fold. With phosphate present, the Ca2+ flux was sufficient to induced precipitation. Generally, the first solid formed was amorphous. The amorphous precipitate, however, was unstable and converted to an apatite-like crystalline phase. Both carbonate (26 mM) and Mg2+ (0.8 mM) in the reaction solution delayed but did not prevent the conversion. The possible relevance of these findings to matrix vesicle calcification is discussed.

Biological Transport↗
PubMed1983

Exploration of the role of phenolsulfotransferase in the disposition of serotonin in human platelets: implications for a novel therapeutic strategy against depression.

Human platelets have been used as models to evaluate a possible role for phenolsulfotransferase (PST) in the disposition of 5-hydroxytryptamine (5HT). The platelet M-type PST, which prefers biogenic amines as substrates, appears to be unique in its ability to O-sulfate dopamine and 4,6-difluoro-5HT (diF-5HT) at rates 6-20 times faster than 5HT. The assay technique employed can make a critical difference in the measured rates of sulfation of these amines, however. For example, use of purified alveolysin toxin to disrupt cell membranes can result in as much as a 20-fold increase in the observed velocity of 5HT O-sulfation. In intact platelets, only 1-3% of the total amount of radiolabelled material (as measured by a thin-layer chromatographic procedure) is the O-sulfate conjugate of 5HT. Up to 20% of the total H3-5HT taken up by cells becomes O-sulfated following treatments such as reserpine which lead to a large increase in the extra-vesicular (cytoplasmic) pool of H3-5HT. Availability of a compound producing irreversible inhibition of M-type PST activity would facilitate exploration of intra-platelet 5HT metabolism, but compounds reported to inhibit essentially 100% of the PST activity in other systems do not appear to interfere with the action of human platelet M-type PST. Because of the apparent similarity between PST present in human platelets and in nerve microsacs prepared from guinea pig brains, PST inhibitors effective in human platelets might also be valuable for studies of amine metabolism in brain tissue. Possible candidates are discussed. Furthermore, the behavioral effects of compounds proving to be PST inhibitors could provide novel therapeutic approaches to the problem of depressive illness.

Antidepressive Agents↗
PubMed1983

Utilization of indole compounds by Cryptococcus neoformans to produce a melanin-like pigment.

Several indoles served as substrates for the phenoloxidase of Cryptococcus neoformans and resulted in the production of a melanin-like pigment. In general, a higher percentage of C. neoformans var. neoformans (A and D serotypes) isolates could produce pigment from indoles than could those of var. gattii (B and C serotypes). Only compounds with a hydroxyl or an amino group on the phenyl ring produced pigment; methoxy, nitro, methyl, and fluorine substituents on the phenyl ring were inactive, as was a hydroxyl group at the 2 position on the indole ring. The phenoloxidase of C. neoformans thus appears to differ from that found in Mycobacterium leprae, which cannot use a hydroxyindole, desoxyfructo-5-hydroxytryptamine, as a substrate. In addition, C. neoformans differs from M. leprae in that desoxyfructo-5-hydroxytryptamine does not inhibit the uptake of dihydroxyphenylalanine into the cell.

Cryptococcus↗
PubMed1982

Preferential accumulation of lithium in the dense bodies of human platelets.

From 50 to 73% of the lithium contained in platelets of patients receiving oral therapy with lithium carbonate was released by brief thrombin treatment. Similarly, about 50% of the lithium in platelets of normal volunteers incubated with lithium chloride was thrombin-releasable. The data indicate that an amount of lithium approximately equal to 10% of the calcium content was sequestered in the dense bodies (amine storage organelles) of human platelets. Electron microprobe analysis of dense bodies suggests that the addition of lithium did not change the phosphorus content but produced a loss of about 10% of the dense-body calcium. Nevertheless, synthetic solid analogues of the dense-body core incubated with lithium chloride did not sequester lithium preferentially over potassium and failed to exchange calcium for lithium. Thus, the mechanism responsible for the observed changes in platelet dense bodies may be related to selective membrane permeability properties rather than to binding of lithium to nucleotides or pyrophosphate in the dense-body core.

Blood Platelets↗
PubMed1982

Uptake of 6-fluoro-5-hydroxytryptamine and 4,6-difluoro-5-hydroxytryptamine into releasable and non-releasable compartments of human platelets.

1 The ring-fluorinated compounds, 6-fluoro-5-hydroxytryptamine and 4,6-difluoro-5-hydroxytryptamine, are sterically similar to 5-hydroxytryptamine (5-HT) but have pKaS for their 5-hydroxyl groups (9.7 and 8.0 respectively) which are lower than that of 5-HT. 2 The rates at which [3H]-5-HT, [3H]-6-fluoro-5-HT, and [3H]-4,6-difluoro-5-HT entered the releasable (vesicular) and non-releasable compartments of washed human platelets during a 1 min incubation period at 37 degrees C were similar. These portions of the uptake process therefore appears to be relatively independent of the pKa of the 5-hydroxyl group. 3 The [3H]-4,6-difluoro-5-HT was unique since material accumulated in the non-releasable compartment during uptake did not migrate into the vesicular compartment under appropriate incubation conditions. 4 The data suggest that the zwitterionic form of 5-HT is not the transported species, but that the electronic configuration about the 5-hydroxyl group may be critical for translocation from a non-releasable to a releasable compartment.

Blood Platelets↗
PubMed1981

Improved detail in biological soft X-ray microscopy: study of blood platelets.

Improved image quality in soft x-ray contact microscopy can be obtained by examining the resist with transmission rather than scanning electron microscopy. Application of the new technique to air-dried preparations of human blood platelets reveals structures not visible in the same cells with transmission electron microscopy or when the resist is examined by scanning electron microscopy. As seen by the new technique, platelet pseudopods contain a central structure connected to a network in the platelet and dense bodies exhibit a lamellar structure.

Blood Platelets↗
PubMed1981

Anomalous compartmentation of 5-hydroxytryptamine in intact human platelets.

1 The movement of radiolabelled 5-hydroxytryptamine (5-HT) between the extracellular medium, the thrombin-releasable (vesicular) compartment, and a non-thrombin-releasable compartment has been investigated in washed human platelets. 2 Appreciable amounts of extracellular 5-HT can accumulate in a non-releasable compartment. Depending on the incubation conditions and the amount of 5-HT already present inside the cell, non-releasable 5-HT can either remain non-releasable or rapidly migrate into the vesicular compartment. 3 Measurable amounts of vesicular 5-HT can also enter a non-releasable compartment. However, vesicular 5-HT which becomes non-releasable does not appear to mix with 5-HT becoming non-releasable following uptake from the extracellular medium. 4 Extracellular 5-HT can be added to vesicles and to the non-releasable compartment in the presence of appreciable quantities of 5-HT already in one or both compartments. 5 The vesicular and non-releasable compartments appear to accumulate 5-HT independently of one another. Furthermore, most vesicular accumulation of 5-HT occurs from the extracellular medium, rather than by translocation of non-releasable 5-HT into the vesicular compartment.

Biological Transport↗
PubMed1981

Applicability of models for carrier-mediated serotonin transport to pools of serotonin in intact human platelets.

Intact human platelets can accumulate serotonin (5HT) in compartments which are vesicular (thrombin-releasable) or extra-vesicular (non-thrombin-releasable). 1. The net accumulation of extracellular 5HT in either compartment is not coupled in a reciprocal fashion to the presence of appropriate sodium gradients across the cell plasma membrane, and 5HT already present in either compartment is not removed when trans-membrane sodium gradients are abolished or reversed. 2. Net counter-transport of 5HT in either compartment is not detectable. 3. The data are not consistent with transport models such as that for glucose in which appropriate sodium gradients produce gradients of a co-transported molecule, or with models in which counter-transport can occur.

Biological Transport↗
PubMed1981

Phosphorus and divalent cations in dog, rabbit, and human platelet dense bodies as deduced from electron microprobe studies of air-dried whole mounts.

Dense bodies have been examined by electron microprobe techniques in air-dried whole mounts of dog, rabbit, and human platelets. On the basis of measurement of the intensities of the X-rays produced when dense bodies are probed for 100 seconds, dog and rabbit platelet dense bodies contain on the average less phosphorus and calcium, but more magnesium, than do human platelet dense bodies. Dense bodies of dog and rabbit platelets thus appear to resemble more closely those of pig platelets than those of human platelets.

Animals↗
PubMed1981

Utility of ten-second uptake periods for kinetic studies of serotonin uptake by intact platelets.

When washed human platelets accumulate serotonin (5HT), it is possible with the use of formaldehyde fixative to measure uptake over periods as short as 10 seconds. To evaluate the utility of these short times for kinetic studies of 5HT uptake, we have examined the accuracy with which the 10 second uptake rate reflects changes in the extracellular 5HT concentration. The amount of 5HT taken up over a 10 second period appears to be determined by the concentration of 5HT present in the extracellular medium during that time period, and the uptake rate can change rapidly following sudden changes in the extracellular 5HT concentration. However, the extent of inhibition of 5HT uptake in the presence of imipramine of extracellular 5HT concentrations greater than 10-5M is somewhat different depending on whether the 5HT is allowed to accumulate for a 10-second or a 5- or 10-minute uptake period. A 10-second uptake period thus appears to be useful for kinetic studies of initial 5HT uptake velocities under normal conditions, but under inhibitory conditions may give results differing from those obtained with minute-long periods.

Blood Platelets↗
PubMed1980

Nuclear magnetic resonance studies of blood platelets.

Blood platelets contain membrane-enclosed granules which have inside them high concentrations of 5-hydroxytryptamine (serotonin) along with adenine nucleotides and divalent metal ions. 19F n.m.r. of fluorinated serotonin incorporated into the granules of both human and pig intact platelets has shown that the motional state of the serotonin is restricted. Comparison with 31P n.m.r. experiments indicates that this restriction of motion is a consequence of high molecular weight aggregates formed by the adenine nucleotides and metal ions, and that it varies with the species from which the platelets are obtained. In the case of human platelet granules, at least, these high molecular weight aggregates are present in the absence as well as in the presence of serotonin. The biological significance of these data is briefly discussed.

Adenine Nucleotides↗