The Purification of Bovine Thyroid Plasma Membranes and the Properties of Membrane-bound Adenyl Cyclase

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

In this study, several lines of evidence are provided to show that Na + , K + -ATPase activity exerts vital roles in normal brain development and function and that loss of enzyme activity is implicated in neurodevelopmental, neuropsychiatric and neurodegenerative disorders, as well as increased risk of cancer, metabolic, pulmonary and cardiovascular disease. Evidence is presented to show that fluoride (F) inhibits Na + , K + -ATPase activity by altering biological pathways through modifying the expression of genes and the activity of glycolytic enzymes, metalloenzymes, hormones, proteins, neuropeptides and cytokines, as well as biological interface interactions that rely on the bioavailability of chemical elements magnesium and manganese to modulate ATP and Na + , K + -ATPase enzyme activity. Taken together, the findings of this study provide unprecedented insights into the molecular mechanisms and biological pathways by which F inhibits Na + , K + -ATPase activity and contributes to the etiology and pathophysiology of diseases associated with impairment of this essential enzyme. Moreover, the findings of this study further suggest that there are windows of susceptibility over the life course where chronic F exposure in pregnancy and early infancy may impair Na + , K + -ATPase activity with both short- and long-term implications for disease and inequalities in health. These findings would warrant considerable attention and potential intervention, not to mention additional research on the potential effects of F intake in contributing to chronic disease.

Cloning and expression of a brain-derived TSH receptor

Several hormones not only regulate the activity of endocrine cells and non-endocrine tissues but also serve as neuronal transmitters or modulators of neuronal activity. Accordingly, the expression and physiological significance of hormonal receptors in the central nervous system (CNS) could be demonstrated for a whole set of hormones (e.g. hCG/LH, GH, T3, CRF, TRH). The G-protein coupled TSH receptor is densely expressed in the thyroid gland and mediates the production and secretion of thyroid hormones. Not all TSH effects, especially in neurological and psychiatric disease states, can readily be explained by the action of the hormone on the thyroid gland and/or TRH levels. Therefore, it has been suggested that TSH might exert its effects directly in the CNS, although no direct proof for a TSH receptor in the human brain has been provided yet. Here we describe the cloning of a TSH receptor from an ovine hypothalamic cDNA library that is similar to thyroid derived cDNA clones. The comparison of amino acid sequences indicates that several protein domains important for the function and activity of the receptor are highly conserved. RT-PCR and RNA protection assay demonstrated that the TSH receptor mRNA is widely expressed throughout the ovine brain. The expression of a TSH receptor in the CNS indicates that TSH is not only a hormonal messenger for the thyroid gland but can also act directly in the brain. Further studies should focus on the physiological role of TSH in the CNS and the regulation of TSH receptor expression in the mammalian brain.

Effects of calcium and calmodulin on the binding of rat parotid secretion granules to the plasma membrane

Since numerous studies suggest that Ca++ and calmodulin may modulate the fusion of secretion granules to the plasma membrane which takes place in exocytosis, we have examined the role of calcium and calmodulin in the binding of isolated parotid secretion granules to plasma membrane vesicles. 125I-labeled inside-out plasma membrane vesicles were incubated with secretion granules, the mixture was layered over 20% sucrose, the gradient was centrifuged, and the amount of 125I in the granule pellet was determined. Addition of Ca++ (20 nM to 10 microM) produced a concentration-dependent increase in the binding of 125I-labeled plasma membrane vesicles to the secretion granules, reaching a maximum value at 10 microM free Ca++; half-maximal binding occurred at 400 nM. Neither right-side-out parotid plasma membrane vesicles nor inside-out pancreatic islet plasma membrane vesicles bound to granules in the presence of 1 microM Ca++. Calmodulin produced a concentration-dependent increase in binding above that of Ca++ alone, and this effect was inhibited by the calmodulin antagonists, trifluoperazine and calmidazolium. Incubation of secretion granules with octadecylrhodamine B (R18)-loaded inside-out plasma membrane vesicles and 2 microM Ca++ caused de-quenching of fluorescence, indicating that the lipids in the granule membrane and the plasma membrane had intermixed. Added calmodulin increased the fluorescence two-fold above that with Ca++ alone. These results suggest that Ca++ and calmodulin may play a role in parotid gland exocytosis by modulating the interaction between the secretion granules and plasma membrane.

Heterogeneity of TSH receptor-binding antibodies in Hashimoto's thyroiditis and Graves' disease

The possible heterogeneity of TSH receptor antibodies in Graves' disease (GD) and Hashimoto's thyroiditis (HT) with respect to the binding site on the receptor and corresponding biological effect was studied. Employing an immunoprecipitation assay (IPA), the sera of 80% of the patients with GD (24 out of 30) and 76% of the patients with HT (16 out of 21) contained TSH receptor-binding antibodies, compared to none of the sera from 17 normal volunteers and 8 patients with nontoxic multinodular goiter. TSH inhibited immunoprecipitation by GD and HT sera. In HT sera (n = 9), but not in GD sera (n = 5), heterogeneity of the TSH-induced inhibition was observed. Four HT sera showed complete inhibition of immunoprecipitation at a saturating concentration (19.8 nM) of TSH. Five HT sera, like the 5 GD sera, showed partial inhibition of immunoprecipitation by 19.8 nM TSH. Thyroid stimulating immunoglobulins (TSI) were found in four of the five GD sera and in only one of the nine HT sera. The results suggest that different subpopulations of TSH receptor antibodies, characterized by other receptor binding sites or different affinities, are associated with autoimmune thyroid disease.

Can the inhibition of prostaglandin synthesis affect the adenylate cyclase response to thyroid stimulating antibodies?

The majority of Graves' immunoglobulins have the capacity to stimulate thyroid adenylate cyclase (AC) activity in vitro. So far, the exact events leading to AC activity stimulation by thyroid stimulating antibody (TSAb) are not known. It has been suggested that TSAb activates thyroid AC through prostaglandin (PG) synthesis, implying the concept that TSH and TSAb stimulate AC in different ways. If this is so, the inhibition of PG synthesis should notably reduce the response of thyroid plasma membrane to TSAb. We have, therefore, investigated the effect of 2 inhibitors of PG synthesis on the TSAb-stimulated AC activity in a crude human thyroid plasma membrane preparation. Neither indomethacin, nor hydrocortisone, even at concentrations able to completely inhibit PG synthesis, had any significant effect on the thyroid plasma membrane response to TSAb. The results suggest, therefore, that, at least under our experimental conditions, PG does not mediate the AC activation by TSAb. Consequently, the aforementioned suggestion should not be used to claim that TSH and TSAb activate thyroid AC through different pathways. The data, however, do not exclude that TSAb may determine PG synthesis in thyroid cells through the phosphatidylinositol signal system (Pl system).

Separation and analysis of two plasma membrane fractions from bovine thyroid which differ in TSH binding and TSH activation of adenylate cyclase

A tissue disruption technique leading to the separation of thyroid epithelial cell components from interfollicular material has been used to study the distribution and the properties of membrane adenylate cyclase originating from intraglandular thyroid and non-thyroid cells. Bovine thyroid fragments were forced through a metallic sieve. The material which filtrates was composed of open cells and cell debris (fraction A); the material remaining on the sieve contained the basal lamina and the interfollicular material as shown by photon and electron microscopic observations (fraction B). Homogenates (HA and HB) were prepared from fractions A and B and centrifuged on a 41% sucrose layer to prepare membrane fractions: MA and MB, which were tested for the presence of adenylate cyclase, TSH-responsive adenylate cyclase and 125I-labelled TSH binding activity. HA and HB contained respectively 70% and 30% of the total thyroid adenylate cyclase activity. MA and MB were similarly enriched in 5'-nucleotidase and adenylate cyclase: 8- to 10-fold as compared to the corresponding homogenates. MA and MB exhibited a marked difference in the response to TSH: TSH either alone or in the presence of Gpp(NH)p stimulated the adenylate cyclase of MA and did not have any effect on MB. Fractionation of MA by isopycnic centrifugation on Percoll gradients yielded a membrane peak exhibiting a TSH-responsive adenylate cyclase activity and a 125I-labelled TSH binding activity displaceable by an excess of unlabelled TSH. A membrane peak at the same density was obtained from MB but its adenylate cyclase did not respond to TSH and there was no specific binding of labelled TSH. Our data indicate that an important fraction of membrane adenylate cyclase of the thyroid does not seem to be coupled with TSH receptor; the major part of this fraction (MB) likely originates from intraglandular non-thyroid epithelial cells. The separation of this membrane fraction from the thyroid cell plasma membrane fraction (MA) allows to increase the response of this latter fraction to TSH.

Solubilized human thyrotrophin receptors behave as one class of high-affinity binding sites

Evidence is presented justifying the conclusion that, in contrast to the dextran-coated charcoal technique, the widely used technique of separating bound and free TSH with polyethylene glycol is inadequate and yields inaccurate results. Optimum values for the concentration of Triton X-100, pH, salts, temperature and time of incubation were established for the TSH-TSH receptor interaction. According to Scatchard analysis, soluble TSH receptors behaved as one class of binding sites. The affinity constant for this class of binding sites (Ka 1.3 X 10(9) M-1) is identical to that for the high-affinity binding sites found in human thyroid membranes (Ka 1.2 X 10(9) M-1). No low-affinity binding sites could be detected after solubilization of membrane receptors. Chromatography experiments on Sepharose CL-6B indicated that, in excess TSH, each micelle containing TSH receptors (molecular weight 150 000) binds 4 [125I]TSH molecules. These data, together with the absence of low-affinity binding sites, led to the hypothesis that high-affinity TSH binding sites may be formed by the clustering of 4 low-affinity binding sites. Cross-reactivity experiments showed that both alpha- and beta-subunits are involved in the binding of TSH to its receptor; the TSH beta-subunit showed an increased cross-reactivity with soluble receptors.

Biochemical and morphological characterization of a plasma membrane-enriched fraction from bovine parathyroid cells

A fraction of enriched plasma membranes from bovine parathyroid cells has been prepared by differential centrifugation. Biochemical characterization shows that this fraction has a specific activity enrichment of 7.2-fold in ouabain-sensitive Na+-K+ ATPase, and 3.5-fold in 5'-nucleotidase. Less than 4% of the total mitochondria and lysosomes are present within the plasma membranes, while microsomal contamination accounts for 14% of total specific activity. Parathyroid hormone radioimmunoassay also reveals the presence of some secretory granules within the plasma membrane fraction. The characteristic morphological aspect of the unusual surface membrane is shown by freeze-fracture electron microscopy. In the enriched pellets, vesicles identified as having a plasma membrane origin have variable sizes, and 50% show an inside-out conformation. Even though the plasma membrane fraction described herein is not absolutely free from contamination by other subcellular components, this protocol represents the first attempt to purify surface membrane from parathyroid tissue and provide the starting material for understanding, at a molecular level, the properties of extracellular Ca2+ regulation and its coupling with secretion of parathyroid hormone.

Vanadate and brain adenylate cyclase. Effect of spreading depression

The effect of vanadate on the adenylate cyclase activity of rat cerebral cortex homogenates is described. In the absence of ethyleneglycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA), 10(-6)M vanadate inhibited enzyme activity by 23%, while 10 (-4) M and 10(-3) M stimulated the enzyme by 14 and 90%, respectively. In the presence of 0.2 mM EGTA, 10 (-6) M to 10(-3) M vanadate had only stimulating effects (18-450%). Additive effects of vanadate and noradrenaline on adenylate cyclase activity suggest different sites of action of these agents. Interaction of vanadate with both fluoride and guanyl-5'-yl imidodiphosphate had an apparently competitive character. Adenylate cyclase maximally stimulated by fluoride (10 mM) was inhibited by vanadate. This inhibitory effect was more pronounced in the absence of EGTA. Adenylate cyclase in the homogenates from the rat cerebral cortex in vivo invaded by spreading depression was slightly increased (up to 38%). This effect was abolished by low (10 (-7) M) vanadate. The results suggest that brain adenylate cyclase is stimulated by vanadate via the guanine nucleotide regulatory protein. The mechanism of vanadate's action, its modulation by calcium ions and the possible physiological role of these effects are discussed.

Studies on the cyclic AMP response to thyroid stimulating immunoglobulin (TSI) and thyrotropin (TSH) in human thyroid cell monolayers

Studies were conducted on the cultured human thyroid cell bioassay for thyroid stimulating immunoglobulin (TSI) and thyrotropin (TSH). In confirmation of the data of Kasagi, et al.,15 incubation of human thyroid cells in Hank's balanced salt solution deficient in NaCl increased the sensitivity of the c-AMP response to bovine TSH by approximately one order of magnitude. Half-maximal stimulation was attained at approximately 0.1 mU bTSH/ml. The effect of NaCl in the medium was greater with stimulation by TSI greater than hTSH greater than bTSH. In contract to incubations in NaCl(+)medium, with NaCl(-) medium most (70%-80%) of the c-AMP produced was released into the medium; this proportion remaining relatively constant over a wide range of bTSH and hTSH concentrations. At TSI concentrations higher than 3mg/ml efflux of c-AMP into the medium was significantly diminished. Stimulation by cholera toxin and prostaglandin E of thyroid cell c-AMP generation was not enhanced in NaCl(-) medium, in contrast to stimulation by TSH and TSI. The presence of 10(-4)m cycloheximide in NaCl(+) medium enhanced the c-AMP response to physiological concentrations of TSH. As with NaCl(-) medium, cycloheximide increased the sensitivity but not the maximum response of the c-AMP response to TSH. However no additivity was observed with NaCl(-) medium and cycloheximide. Human thyroid cells obtained from patients with Graves' disease are relatively insensitive to TSI stimulation. In NaCl(-) medium, however, the sensitivity of these cells to TSI stimulation is sufficient to enable them to be utilized in the TSI assay. The present state of the TSI assay is discussed.

Isolation from thyroid cells or purified plasma membranes with associated actin microfilaments. Proteins bound to actin

Plasma membranes of thyroid cells were purified from hog thyroid glands following two procedures. Their homogeneity was tested by electron microscopy and by measurements of the activity of membrane-bound enzyme markers. According to the procedure used the membrane fractions obtained present some differences in their morphological features as well as in the repartition of the activities of the membrane-bound enzyme markers. However, whatever the composition of the membrane fraction examined (membrane vesicles, single membrane sheets with junctional complexes), decoration with heavy meromyosin clearly shows the presence of actin filaments attached to these fragments. Analysis of proteins by polyacrylamide gel electrophoresis indicates the presence of about twelve major components with actin. Treatment of membranes with Triton X-100 results in an insoluble core which contains all the actin and most of the major proteins. The selective extraction of these components by buffers differing in their ionic strength, pH, or the presence or absence of ATP X Mg has been used to characterize some of the proteins associated to actin; among them are filamin, myosin, alpha-actinin, tropomyosin.

Effect of proteolytic and lipolytic enzymes on the adenylate cyclase activity from brain membranes of Ceratitis capitata

1. The effect of various proteolytic enzymes was assayed on the adenylate cyclase activity in purified brain membrane preparations from the insect Ceratitis capitata. Trypsin, chymotrypsin, papain, thermolysin, elastase, subtilisin and prot. XIV were examined. 2. Trypsin treatment, at 37 degrees C, decreased the adenylate cyclase activity even in the presence of GppNHp that protects the activity from the thermal inactivation. 3. Residual basal, GppNHp- and F(-)-stimulated activities were similar when membrane preparations were preincubated either in the presence or in the absence of GppNHp and F-. 4. All proteolytic activities assayed on the brain membrane preparations, excepting papain, exerted an inhibition of adenylate cyclase in basal conditions. 5. The inhibition was stronger in the presence of F- than in the presence of other regulators. 6. Papain showed also a notable inhibition of adenylate cyclase in the presence of F-. 7. Phospholipase A2 treatment decreased both basal and stimulated activity; however, F(-)-sensitive activity was less affected than basal and GppNHp-sensitive activity. F(-)-stimulated activity was less affected by phospholipase A2 than either basal or GppNHp-stimulated activities. 8. Phospholipids are, then, essential for the highest basal activity, although the relationship between catalytic and nucleotide-regulatory components was unaffected by this treatment.

The formation of sphingomyelin from phosphatidylcholine in plasma membrane preparations from mouse fibroblasts

The enzymatic formation of radioactive sphingomyelin from [14C]choline-labeled phosphatidylcholine was demonstrated to reside exclusively in the plasma membrane fraction of mouse fibroblasts. This activity has several properties in common with the phosphatidylcholine ceramide phosphocholine transferase of mouse liver microsomes. The enzyme has little if any phospholipase C activity and isotope dilution experiments suggest that phosphatidylcholine is the substrate rather than it is converted to CDP choline, phosphocholine, free choline or glycerophosphocholine prior to the transfer reaction. The activity is stimulated by the addition of bovine serum albumin and MnCl2 to the incubation mixtures. The plasma membrane localization of the enzyme suggests that it may have a central role in the biosynthetic pathways for sphingomyelin in mouse fibroblasts.

An enriched preparation of basal-lateral plasma membranes from gastric glandular cells

A procedure is described for the preparation of a membrane fraction enriched in basal-lateral plasma membranes from gastric mucosa. Gastric glands isolated from rabbit were employed as starting material, greatly reducing contamination from non-glandular cell types. The distribution of cellular components during the fractionation procedure was monitored with specific marker enzymes. (Na+ + K+)-ATPase, ouabain-sensitive K+-stimulated p-nitrophenyl-phosphatase and histamine-stimulated adenylate cyclase were used as markers for basal-lateral membranes. These three markers were similarly distributed during both differential and equilibrium density gradient centrifugation. The enriched membrane fraction contained more than 30% of the total initial activities of the three basal-lateral membrane markers which were purified better than 11-fold with respect to protein. (Na+ + K+)-ATPase activity was resolved from the activities of acid phosphatase, pepsin, Mg2+-ATPase, cytochrome c oxidase, NADPH-cytochrome c reductase, glucose-6-phosphatase, (K+ + H+)-ATPase, DNA and RNA.

Thyroid hormone binding to plasma membrane preparations: studies in different thyroid states and tissues

Two orders of high-affinity saturable binding sites for L-T4 and L-T3 were evidenced in purified plasma membrane preparations from rat liver (apparent equilibrium dissociation constant KD for T4 congruent to 0.6 and 23 nM, for T3 congruent to 9 and 237 nM) and kidney (KD for T4 congruent to 4 and 127 nM; for T3 congruent to 15 and 270 nM). Differences of statistical significance were only found for the higher affinity T4 binding site. In contrast, no saturable T4 or T3 binding could be detected in spleen plasma membranes. Testis plasma membranes exhibited 2 sets of T4 binding sites but with a lower affinity than in liver and kidney (KD congruent to 28 and 286 nM), and only one set of T3 binding sites (KD congruent to 266 nM). A good correlation was found between the plasmalemma T4 and T3 binding properties of a tissue and its ability to respond to and/or metabolize thyroid hormones. T4 and T3 binding was also examined in liver plasma membranes of rats under various thyroid status; no difference could be detected in either KD or total capacity for both sets of T4 and T3 binding sites when comparing normal with hyper- or hypothyroid rats. The distribution of plasmalemma high-affinity specific T4 and T3 binding sites in different tissues suggests that these sites are involved in hormone action, or in the transport of these hormones within the cell.

Preliminary characterization of calcium binding in islet-cell plasma membranes

Preliminary characterization of calcium binding was determined in a highly-enriched islet-cell plasma membrane fraction using a membrane filtration technique. Equilbrium calcium binding was specific, concentration dependent and saturable. Scatchard analysis indicated the existence of more than one class of calcium binding sites. The affinity constants and maximum binding capacities were 1.14 X 10(5) M-1 and 1.2 picomol/microgram protein and 1.17 X 10(3) M-1 and 64.8 picomol/microgram for the high and low affinity sites, respectively. Bound 45Ca2+ was dissociate from the plasma membranes in a biphasic manner in the presence of excess unlabelled calcium.

Localization of 3',5'-cyclic adenosine monophosphate phosphodiesterase (cAMP-PDEase) activity in isolated bovine thyroid plasma membranes

Isolated bovine thyroid plasma membrane preparations were obtained by isopycnic density gradient centrifugation. Cyclic AMP-PDEase (EC 3.1.4.c) activity has been demonstrated by electron microscopic histochemistry on the unit membrane of isolated bovine thyroid cells. 3-isobutyl-1-methyl-xanthine (IBMX) produced partial inhibition, while omission of the substrate revealed no reaction product deposition. These observations correlated well with biochemical studies that showed 0.4% of the total cAMP-PDEase activity to be present in the plasma membrane preparations. Kinetic analysis of cAMP hydrolysis yielded two apparent Michaelis constants for the homogenate and the plasma membrane-rich fraction. Dose-response curves for IBMX inhbition showed cAMP-PDEase of the homogenate to be more sensitive to inhibition than that of the plasma membrane-bound enzyme. Furthermore, wash experiments indicate that the plasma membrane-associated enzyme is tightly bound. This investigation strengthens our previous study and suggests that bovine thyroid cell plasma membranes contain a cAMP-PDEase that may be involved in interactions between the cell and the external environment in a manner yet to be determined.

The subcellular biochemistry of thyroid

In this review the subcellular localization of enzymes and constituents in thyroid is discussed. Conditions and results of differential pelleting and gradient centrifugation studies are described with special attention to the validity of the markets used (Table VI). Special approaches to the isolation and characterization of thyroid organelles and membranes are extensively reviewed (Table VII). Subcellular fractionation of thyroid tissue has been shown to be an arduous task. Classic approaches for differential pelleting and gradient centrifugation, which have been proved successful for rat liver, are not always equally satisfactory for thyroid. The major problem is the toughness of the tissue requiring rather traumatizing homogenizing procedures. Nevertheless, the fractionation procedures did allow the subcellular localization of some enzymes and constituents to be established with a high degree of certainty. Furthermore, enriched subcellular fractions have been isolated which have been useful for biochemical studies concerning the specific function of this tissue.

Multiple effects of guanine nucleotides on human platelet adenylated cyclase

We report that the adenylate cyclase system in human platelets is subject to multiple regulation by guanine nucleotides. Previously it has been reported that GTP is either required for or has little effect on the response of the enzyme to prostaglandin E1. We have found that when platelet lysates were prepared in the presence of 5 mM EDTA, GTP lowered the basal and prostaglandin E1-stimulated adenylate cyclase activity, but at a higher concentration of Mn2+, it caused an increase in enzyme activity exceeding that occurring in the presence of prostaglandin E1. In the presence of Mn2+, dGTP mimics the effect of GTP and is 50% as effective as GTP. Our data suggest that the inhibitory effect of GTP on prostaglandin E1-stimulated adenylate cyclase is mainly due to its direct effect on the enzyme itself, whereas the stimulatory effect of GTP on prostaglandin E1-stimulated adenylate cyclase is due to enhancement of the coupling between the prostaglandin E1 receptor and adenylate cyclase. These studies also indicate that the method of preparation of platelet lysates can profoundly alter the nature of guanine nucleotide regulation of adenylate cyclase.

The differential effect of thyrotropin on the electrical responses of thyroid cells in monolayer cultures of varying duration

The acute effects of thyrotropin on the membrane potential of thyroid cells maintained in the presence or absence of thyrotropin (0.2 U/ml) in the culture medium was determined. Monolayer cultures were prepared from porcine thyroid glands and cultured for 4--17 days after which the culture medium was exchanged for a buffered salt solution for intracellular measurements of the membrane potential. Cells were serially impaled with a microelectrode, first in the absence and then in the presence of 10 mU/ml thyrotropin. Cells cultured for 4--9 days depolarized from --29.6 +/- 1.7 (mean +/- S.E.) to --19.3 +/- 1.3 mV within 10 min after acute addition of 10 mU/ml thyrotropin. From 11 to 17 days of culture, basal membrane potentials were lower and, in most instances, cell hyperpolarization occurred within 30 min in response to thyrotropin. There was no difference in the electrical response of cells maintained in culture with or without thyrotropin. However, cells cultured with thyrotropin formed follicle-like structures in contrast to the monolayer formation of cells cultured without thyrotropin. The changes in the basal and stimulated electrical responses occur within a time frame similar to that reported for changes in the biosynthetic capacity of thyroid cells in culture. The data further emphasize the possible regulatory role of the cell membrane in stimulus-secretion coupling in the thyroid.

Thyroid adenylate cyclase stimulating immunoglobulins in thyroid diseases

The occurrence of serum immunoglobulins with capacity to stimulate thyroid adenylate cyclase (TSAb) was studied in seventy-two healthy volunteers and 120 unselected patients with various thyroid diseases. A high frequency of TSAb (82.5%, P less than 0.00006) was found in Graves' disease, while TSAb was present only in 13--20% of serum from patients with nontoxic nodular goitre, nontoxic diffuse goitre, toxic adenoma, toxic nodular goitre and myxoedema. These patients had low level of TSAb compared to patients with Graves' disease. In patients with Graves' disease there was no correlation between the level of TSAb and hormonal status except serum triiodothyronine (rs = 0.29, P less than 0.05), and no relation with eye involvement or presence of microsomal thyroid antibodies was found. The results indicate that the human thyroid adenylate cyclase assay system with 1 hour incubation periods is a sensitive method for detection of immunoglobulins with TSH-like capacity to stimulate the thyroid gland.

Characterization of specific differences in protein phosphorylation of the plasma membrane and the endoplasmic reticulum of mouse fibroblasts

Endogenous phosphorylation was studied with highly purified fractions of the plasma membrane and the endoplasmic reticulum of SV40-transformed mouse fibroblasts using [gamma-32P]ATP and [gamma-32P]GTP as precursors. With ATP maximum overall incorporation of 32P into both membrane fractions occurred at pH 7.8 in the presence of 10 mM MgCl2 after incubation for 1 min. GTP could be utilized only by the plasma membrane fraction showing maximum incorporation of 32P at pH 7.8 and 10 mM MgCl2 after incubation for 3 min. The pattern of phosphoproteins of the plasma membrane is represented by more than 15 proteins whereas the endoplasmic reticulum essentially contained only one phosphorylated component of 35 000 molecular weight. The comparison of ATP- and GTP-specific phosphorylation of the plasma membrane revealed GTP to be a less efficient precursor yielding a similar phosphoprotein pattern with one significant difference: the GTP-specific main component exhibited a molecular weight of about 100 000 and the ATP-specific main component a molecular weight of 110 000. The relative distribution of individual phosphoproteins in the pattern of the plasma membrane was dependent on pH but not on MgCl2 concentration or time of incubation. Increasing concentrations of plasma membrane protein altered the patterns of phosphoproteins dramatically: At high protein concentrations the ATP-specific main component (Mr = 110 000) was no more phosphorylated whereas with GTP the main component Mr = 100 000 was essentially the sole phosphorylated protein.

Effects of phospholipase A2 and filipin on the activation of adenylate cyclase

Rat liver plasma membranes were incubated with phospholipase A2 (purified from snake venom) or with filipin, a polyene antibiotic, followed by analysis of the binding of glucagon to receptors, effects of GTP on the glucagon-receptor complex, and the activity and responses of adenylate cyclase to glucagon + GTP, GTP, Gpp(NH)p, and F-. Phospholipase A2 treatment resulted in concomitant lossess of glucagon binding and of activation of cyclase by glucagon + GTP. Greater than 85% of maximal hydrolysis of membrane phospholipids was required before significant effects of phospholipase A2 on receptor binding and activity response to glucagon were observed. The stimulatory effects of Gpp(NH)p or F- remained essentially unaffected even at maximal hydrolysis of phospholipids, whereas the stimulatory effect of GTP was reduced. Detailed analysis of receptor binding indicates that phospholipase A2 treatment affected the affinity but not the number of glucagon receptors. The receptors remain sensitive to the effects of GTP on hormone binding. Filipin also caused marked reduction in activation by glucagon + GTP. However, in contrast to phospholipase A2 treatment, the binding of glucagon to receptors was unaffected. The effect of GTP on the binding process was also not affected. The most sensitive parameter of activity altered by filipin was stimulation by GTP or Gpp(NH)p; basal and fluoride-stimulated activities were least affected. It is concluded from these findings that phospholipase A2 and filipin, as was previously shown with phospholipase C, are valuable tools for differentially affecting the components involved in hormone, guanyl nucleotide, and fluoride action on hepatic adenylate cyclase.

A possible reason for the phalloidin tolerance of hepatoma cells

In contrast to normal liver cells, AS-30D hepatoma cells are insensitive to phalloidin. The lack of the typical phalloidin response in the latter cells is not due to a deficiency of contractile proteins. Actin prepared from hepatoma cells is able to form filamentous structures and is stabilized in a manner similar to muscle actin. Isolated liver cells were exposed to a medium containing phalloidin and removed after 20 min by centrifugation. The supernatant was incubated again with fresh cells. The procedure was repeated four times. The phalloidin response decreased to about 19% of the control because of the uptake of phalloidin during each incubation. When the same procedure was carried out with AS-30D hepatoma cells, and aliquots of the supernatants were tested with hepatocytes no marked decrease of the phalloidin response was seen. This indicates that hepatoma cells do not consume the toxin as do normal liver cells.

Cyclic nucleotides in nervous tissue

A review of the literature emphasizes that cyclic nucleotides play a key role in regulation of cell growth, differentiation and metabolism in diverse tissues and, in addition, are closely involved in neural tissue function. The role of cAMP as a second messenger is discussed.

The adenylate cyclase-cyclic AMP-phosphodiesterase system in pathological human thyroid

The adenylate cyclase-cyclic AMP-phosphodiesterase system of human thyroid tissues adjacent to cold nodules (control), two follicular adenomas, one hyperplastic thyroid and one hyperfunctioning follicular carcinoma have been compared. In the hyperfunctional follicular carcinoma the basal adenylate cyclase is much higher than in control tissue, carcinoma adenylate cyclase does not respond to TSH and prostaglandin E1, whereas it responds normally to fluoride. In the hyperplastic, but hypofunctional thyroid the basal adenylate cyclase is higher than in normal tissue whereas the response to TSH, PGE1, and fluoride is normal. No difference between the follicular adenomas and normal thyroid stimulated and unstimulated adenylate cyclase was observed. Furthermore in various thyroid tissues no changes in the level of cyclic AMP phosphodiesterase was found. Our data indicate a greater change in the synthesis rather than in degradation of cyclic AMP in the human pathological thyroids studied.

Thyrotropin receptor-adenylate cyclase system in plasma membranes from normal and diseased human thyroid glands

Thyrotropin binding characteristics and adenylate cyclase (AC) activity of thyroid plasma membranes were studied in 52 tissues from normal and diseased human thyroids. Data from normal glands, Graves' goiters, non toxic multinodular goiters and nodular and perinodular tissue of toxic nodular goiters show the same basal, TSH- and NaF- stimulated adenylate cyclase activities (no. = 45; 34.1 +/- 3.2 (m +/- SE), 378 +/- 43, 298 +/- 48 pmol cAMP x min-1 x mg membrane protein-1), the same stimulability of AC by TSH (11.3 +/- 1.4--fold over basal level) and by NaF (8.1 +/- 1.8-fold), the same apparent TSH binding equilibrium constants (5.6 +/- 0.7 and 406 +/- 57 nM) and the same TSH binding site concentrations (2.2 +/- 0.4, 27.8 +/- 5.9 pmol x mg membrane protein-1). Alterations of the TSH receptor and of the AC were detected in membranes from tumoral and metastatic lymph node tissues from thyroid papillary carcinoma and in the thyroid tissue from post-radioiodide therapy thyroiditis. These observations suggest that: (i) hyperthyroidism in Graves' disease or toxic nodular goiter does not result in and is not a consequence of an alteration in the TSH receptor-adenylate cyclase system; (ii) there is no evidence supporting a relationship between the studied membrane properties and clinical or histological status; (iii) membrane abnormalities detected in thyroid carcinoma vary widely; (iv) studies of these membrane alterations might be of interest in the therapeutic management of thyroid carcinoma and may lead to a better understanding of the receptor-adenylate system.

Subcellular structure of bovine thyroid gland. VII. A study on the distribution of bovine thyroid plasma membranes by density gradient centrifugation in zonal rotors

In order to obtain plasma membrane-rich fractions two methods were tried. Approach A was based on differential pelleting followed by discontinous gradient centrifugation in a B-XIV zonal rotor. In approach B homogeneization was performed in buffered water (NaHCO3, pH 7.4). The 73 300 X g pellet from this homogenate was subjected to buoyant density equilibrium in a HS zonal rotor (continuous sucrose gradient). Using approach A, the highest relative specific activity for plasma membrane markers was found at the 30-37% sucrose interphase. However, an increase for glucose 6-phosphatase (endoplasmic reticulum marker) was also found at that interphase. Using approach B marker profiles different from approach A were found. Approach B results in a subdivision of membrane material in four distinct regions. These regions do not contain completely pure membrane species, although region I seems to be essentially derived from plasma membranes. It is also concluded from approach A that plasma membranes from bovine thyroid tissue are heterogeneous.

Regulation of thyroid ornithine decarboxylase by the polyamines. Induction of a protein inhibitor of ornithine decarboxylase by the end-products of the reaction

When spermidine, putrescine or 1,3-diaminopropane was injected (12.5 mumol/100 g body weight) into rats 1 h before thyrotropin, ornithine decarboxylase activity was increased by 75--150% over control levels. However, when greater than or equal to 75 mumol polyamine/100 g body weight was injected, thyrotropin-activated activity was inhibited by 70--95%. Multiple polyamine injections inhibited goitrogen-induced activity and gland weight increase by approx 35%. The polyamines also inhibited thyrotropin-activated rat thyroid ornithine decarboxylase in vitro in a dose-related fashion, with 50% inhibition occurring at 2--5 . 10(-4)M. The inhibition was not due to a direct effect on the enzyme. No stimulation was seen with low concentrations of polyamine. The polyamines had no effect on in vitro thyroid protein/RNA synthesis or glucose oxidation but had a biphasic effect on plasma membrane adenylate cyclase activity. A protein inhibitor to thyroid ornithine decarboxylase was generated in vivo by multiple injections of the polyamines into rats and in vitro by incubating bovine thyroid slices with 2--10 mM polyamine. The inhibitor was non-dialyzable, destroyed by boiling, and its formation was blocked in a dose-related fashion by cycloheximide. We conclude that: (1) thyroid ornithine decarboxylase is subject not only to positive control, but is also negatively regulated by its end-products, the polyamines, which induce a protein inhibitor to ornithine decarboxylase; (2) since gland growth is also inhibited under these conditions, the polyamine effect on thyroid ornithine decarboxylase may be biologically significant.