Arginase is overactive in psoriatic skin.

BACKGROUND: Psoriatic keratinocytes are poorly differentiated and hyperproliferative. Low concentrations of nitric oxide (NO) induce keratinocyte proliferation, while high concentrations induce differentiation. The NO-producing enzyme inducible NO synthase is overexpressed in psoriatic skin, but so is arginase. The overexpressed arginase competes for arginine, the common substrate for both enzymes, and may reduce NO production. OBJECTIVES: To determine whether arginase activity is elevated in psoriatic skin and whether exogenous NO will improve psoriatic plaques. METHODS: Tape strips were taken from healthy skin of eight control subjects and nonlesional skin of eight patients with psoriasis and L-arginine, L-citrulline and L-ornithine concentrations measured by high-performance liquid chromatography. In a second study, four psoriatic patients with a pair of similar symmetrical plaques were treated with an NO donor and vehicle control. Plaques were scored for size, erythema, induration and scaling at the start and after 6 weeks of treatment. RESULTS: Ornithine, the end-product of arginase, was at higher concentrations in nonlesional psoriatic than in healthy skin (mean +/- SEM 2.08 +/- 0.98 vs. 1.13 +/- 0.44 microg mg(-1) protein; P = 0.0002). Arginine, its substrate, was at lower concentrations. Topical application of an NO donor improved psoriatic plaques clinically [mean +/- SD reduction in severity from baseline score (100%) to 35% +/- 16% in active NO donor and to 93% +/- 10% in control]. CONCLUSIONS: Arginase is overactive in psoriatic skin, leading to a relative increase in the consumption of arginine. We therefore hypothesize a relative decrease in NO synthase-derived NO production. NO donors may be effective topical treatments for psoriasis.

Acute hemodynamic changes after rapid intravenous bolus dosing of dexmedetomidine in pediatric heart transplant patients undergoing routine cardiac catheterization.

BACKGROUND: Dexmedetomidine is a highly selective α(2)-adrenoceptor agonist with sedative, anxiolytic, and analgesic properties that has minimal effects on respiratory drive. Its sedative and hypotensive effects are mediated via central α(2A) and imidazoline type 1 receptors while activation of peripheral α(2B)-adrenoceptors result in an increase in arterial blood pressure and systemic vascular resistance. In this randomized, prospective, clinical study, we attempted to quantify the short-term hemodynamic effects resulting from a rapid i.v. bolus administration of dexmedetomidine in pediatric cardiac transplant patients. METHODS: Twelve patients, aged 10 years or younger, weighing ≤40 kg, presenting for routine surveillance of right and left heart cardiac catheterization after cardiac transplantation were enrolled. After an inhaled or i.v. induction, the tracheas were intubated and anesthesia was maintained with 1 minimum alveolar concentration of isoflurane in room air, fentanyl (1 µg/kg), and rocuronium (1 mg/kg). At the completion of the planned cardiac catheterization, 100% oxygen was administered. After recording a set of baseline values that included heart rate (HR), systolic blood pressure, diastolic blood pressure, central venous pressure, systolic pulmonary artery pressure, diastolic pulmonary artery pressure, pulmonary artery wedge pressure, and thermodilution-based cardiac output, a rapid i.v. dexmedetomidine bolus of either 0.25 or 0.5 µg/kg was administered over 5 seconds. The hemodynamic measurements were repeated at 1 minute and 5 minutes. RESULTS: There were 6 patients in each group. Investigation suggested that systolic blood pressure, diastolic blood pressure, systolic pulmonary artery pressure, diastolic pulmonary artery pressure, pulmonary artery wedge pressure, and systemic vascular resistance all increased at 1 minute after rapid i.v. bolus for both doses and decreased significantly to near baseline for both doses by 5 minutes. The transient increase in pressures was more pronounced in the systemic system than in the pulmonary system. In the systemic system, there was a larger percent increase in the diastolic pressures than the systolic pressures. Cardiac output, central venous pressure, and pulmonary vascular resistance did not change significantly. HR decreased at 1 minute for both doses and was, within the 0.5 µg/kg group, the only hemodynamic variable still changed from baseline at the 5-minute time point. CONCLUSION: Rapid i.v. bolus administration of dexmedetomidine in this small sample of children having undergone heart transplants was clinically well tolerated, although it resulted in a transient but significant increase in systemic and pulmonary pressure and a decrease in HR. In the systemic system, there is a larger percent increase in the diastolic pressures than the systolic pressures and, furthermore, these transient increases in pressures were more pronounced in the systemic system than in the pulmonary system.

In vitro comparison of antimicrobial activity of iodine and silver dressings against biofilms.

OBJECTIVE: To compare the antimicrobial effectiveness of silver- and iodine-containing wound dressings against preformed mature biofilms of pathogenic wound bacteria grown in vitro. METHOD: Biofilms of Pseudomonas aeruginosa and Staphylococcus aureus were grown within an in vitro flat bed perfusion biofilm model. Mature biofilms were removed and exposed to wound dressings containing either silver or iodine (Aquacel Ag and Iodozyme) within a static diffusion method, for up to 24 hours. This method was designed to reflect certain key features that determine antimicrobial activity within the wound. The numbers of viable bacteria surviving in the biofilms were determined at set time intervals over the test period. RESULTS: Both test dressings exerted an antimicrobial effect against the target species biofilms, although the iodine dressing was more efficacious under the experimental conditions employed. CONCLUSION: There are large and potentially significant differences (as measured in vitro) in the effectiveness of wound dressings containing broad-spectrum antimicrobial agents such as silver and iodine against specific types of bacterial biofilms.

The investigation and management of back pain in children.

Back pain in children and adolescents is probably much less common than in adults, but its true incidence is unknown. Although back pain has traditionally been considered a rare and often sinister presentation in the paediatric age group, recent literature now suggests that a relatively high number of children do experience back pain, but only a small proportion seek medical attention. For the majority of children with back pain no underlying cause is identified, but some require investigation to exclude serious underlying pathology. Laboratory and imaging investigations should be targeted towards those with "red flag" symptoms and signs. Imaging studies, particularly MRI, have an important role in diagnosis of underlying pathology such as infection or malignancy.

Action of erythropoietin in vitro on rabbit reticulocyte membrane Ca2+-ATPase activity.

The mechanism of action of erythropoietin is thought to require specific interaction with the target cell surface and involve alteration of cellular calcium metabolism. Using the rabbit reticulocyte membrane as a model of the immature red cell membrane, we investigated the effects of human recombinant erythropoietin on membrane Ca2+-ATPase (calcium pump) activity in vitro. Erythropoietin in a concentration range of 0.025 to 3.0 U/ml progressively decreased membrane Ca2+-ATPase activity by up to 64% (P less than 0.01). These concentrations have been shown by others to stimulate in vitro erythroid growth. The action of erythropoietin on reticulocyte Ca2+-ATPase required an incubation time of 1 h before enzyme assay for maximum effect and was neutralized by antierythropoietin antiserum. Other nonhemopoietic growth factors (epidermal growth factor, insulin) had no effect in this assay. Ca2+-ATPase activity of membranes prepared from rabbit mature red blood cells was not inhibited by erythropoietin. The novel effect of erythropoietin on reticulocyte membrane Ca2+-ATPase activity is a mechanism by which erythropoietin can influence cellular Ca2+ metabolism.

Thyroid hormone binding by human serum prealbumin (TBPA). Electrophoretic studies of triiodothyronine-TBPA interaction.

Thyroxine-binding prealbumin (TBPA) in normal human serum has been shown in a polyacrylamide gel electrophoresis system to bind 7-9% of tracer level purified [(125)I]triiodothyronine (T3), and more than 30% of T3 in serum deficient in thyroxinebinding globulin (TBG). The T3-TBPA interaction has been confirmed at pH 9.0 and pH 7.4 in this electrophoretic demonstration of TBPA binding of T3 in serum. Purified human TBPA has also been shown to bind T3. Progressive additions of unlabeled thyroxine (T4) to serum containing tracer [(125)I]T3 displace T3 from TBG, its principal carrier, to TBPA and albumin; however, T4 loading does not lead to significant T3 displacement from TBPA even at T4 levels known to saturate TBPA. Loading of serum with unlabeled T3 results in displacement of more than 50% of [(125)I]T3 from TBPA, as well as from TBG, to albumin. Studies carried out with serum containing diphenylhydantoin (DPH) or MK-185, known inhibitors of T4 binding by TBG, also showed T3 displacement from TBG to TBPA and albumin. Although salicylate and tetraiodothyroacetic acid (TETRAC) displace T4 from sites on TBPA, they have only minimal effects on T3-TBPA interaction.

Role of calmodulin in thyroid hormone stimulation in vitro of human erythrocyte Ca2+-ATPase activity.

Because human erythrocyte membrane Ca2+-ATPase is a calmodulin-dependent enzyme, and because physiological levels of thyroid hormone stimulate this enzyme system in vitro, we have studied the role of calmodulin in this model of extranuclear thyroid hormone action. Ca2+-ATPase activity in the absence of thyroid hormone ("basal activity") was increased by inclusion in the preassay incubation mixture of purified calmodulin or hypothyroid erythrocyte hemolysate that contained calmodulin (39 micrograms calmodulin/ml packed cells, determined by radioimmunoassay); addition of L-thyroxine or 3,5,3'-triiodo-L-thyronine (10(-10)M) significantly enhanced (P less than 0.001) enzyme activity in the presence of calmodulin or hemolysate. The stimulatory effects of thyroid hormone, calmodulin, and hemolysate were additive. At 5-10 microM, trifluoperazine, an antagonist of calmodulin, inhibited thyroid hormone stimulation of Ca2+-ATPase activity. Higher concentrations of trifluoperazine (50-100 microM) inhibited basal and hormone-stimulated enzyme activity, with or without added calmodulin. Anti-calmodulin antibody (10-50 micrograms antibody/mg membrane protein) inhibited basal, calmodulin-stimulated and thyroid hormone-stimulated Ca2+-ATPase activity. Membrane preparations were shown by radioimmunoassay to contain residual endogenous calmodulin (0.27 +/- 0.02 micrograms/mg membrane protein). The latter accounts for the effect of trifluoperazine and calmodulin antibody on membrane Ca2+-ATPase activity in the absence of added purified calmodulin. These results support the conclusion that the in vitro action of physiological levels of iodothyronines on human erythrocyte Ca2+-ATPase activity requires the presence of calmodulin.

Retinoic acid inhibits calmodulin binding to human erythrocyte membranes and reduces membrane Ca2(+)-adenosine triphosphatase activity.

Ca2(+)-ATPase activity in human red cell membranes is dependent on the presence of calmodulin. All trans-retinoic acid inhibited human red cell membrane Ca2(+)-ATPase activity in vitro in a concentration-dependent manner (10(-8) to 10(-4) M). In contrast, retinol, retinal, 13-cis-retinoic acid and the benzene ring analogue of retinoic acid did not alter enzyme activity. Purified calmodulin (up to 500 ng/ml, 3 X 10(-8) M) added to red cell membranes, in the presence of inhibitory concentrations of retinoic acid, only partially restored Ca2(+)-ATPase activity. 125I-Calmodulin bound to red cell membranes was displaced by unlabeled retinoic acid (50% reduction at 10(-8) M retinoic acid), as effectively as by unlabeled calmodulin. Another calmodulin-stimulable enzyme, bovine brain cyclic nucleotide phosphodiesterase, was unaffected by retinoic acid. 8-Anilino-1-naphthalene sulfonic acid bound to calmodulin, studied spectrofluorometrically, was not displaced by retinoic acid. Thus, retinoic acid inhibits calmodulin binding to red cell membranes, reducing calmodulin-stimulable Ca2(+)-ATPase activity. Retinoic acid does not directly interact with calmodulin, but rather exerts its effect by interfering with calmodulin access to the membrane enzyme. These effects occur at physiological concentrations of the retinoid.

The effect of insulin on renal handling of sodium, potassium, calcium, and phosphate in man.

The effects of insulin on the renal handling of sodium, potassium, calcium, and phosphate were studied in man while maintaining the blood glucose concentration at the fasting level by negative feedback servocontrol of a variable glucose infusion. In studies on six water-loaded normal subjects in a steady state of water diuresis, insulin was administered i.v. to raise the plasma insulin concentration to between 98 and 193 muU/ml and infused at a constant rate of 2 mU/kg body weight per min over a total period of 120 min. The blood glucose concentration was not significantly altered, and there was no change in the filtered load of glucose; glomerular filtration rate (CIN) and renal plasma flow (CPAH) were unchanged. Urinary sodium excretion (UNaV) decreased from 401 plus or minus 46 (SEM) to 213 plus or minus 18 mueq/min during insulin administration, the change becoming significant (P smaller than 0.02) within the 30-60 min collection period. Free water clearance (CH2O) increased from 10.6 plus or minus 0.6 to 13 plus or minus 0.5 ml/min (P smaller than 0.025); osmolar clearance decreased and urine flow was unchanged. There was no change in plasma aldosterone concentration, which was low throughout the studies, and a slight reduction was observed in plasma glucagon concentration. Urinary potassium (UKV) and phosphate (UPV) excretion were also both decreased during insulin administration; UKV decreased from 66 plus or minus 9 to 21 plus or minus 1 mueq/min (P smaller than 0.005), and tupv decreased from 504 plus or minus 93 to 230 plus or minus 43 mug/min (P smaller than 0.01). The change in UKV was associated with a significant reduction in plasma potassium concentration. There was also a statistically significant but small reduction in plasma phosphate concentration which was not considered sufficient alone to account for the large reduction in UPV. Urinary calcium excretion (UCaV) increased from 126 plus or minus 24 to 200 plus or minus 17 mug/min (P smaller than 0.01). These studies demonstrate a reduction in UNaV associated with insulin administration that occurs in the absence of changes in the filtered load of glucose, glomerular filtration rate, renal blood flow, and plasma aldosterone concentration. The effect of insulin on CH2O suggests that insulin's effect on sodium excretion is due to enhancement of sodium reabsorption in the diluting segment of the distal nephron.

Pro-angiogenesis action of thyroid hormone and analogs in a three-dimensional in vitro microvascular endothelial sprouting model.

AIM: Our laboratory has recently demonstrated the pro-angiogenesis effects of thyroid hormone in the chick chorioallantoic membrane model. METHODS: Generation of new blood vessels from existing vessels was promoted two- to three-fold by either L-thyroxine (T4) or 3,5,3'-triiodo-L-thyronine (T3) at total hormone concentrations of T7-T9 M. RESULTS: T4-agarose, a formulation of thyroid hormone that does not cross the cell membrane, produced a potent pro-angiogenesis effect comparable to that obtained with T3 or T4. In the present investigation, T3, T4, T4-agarose, and basic fibroblast growth factor, each added to vascular endothelial growth factor, produced comparable pro-angiogenesis effects in the in vitro three-dimensional human microvascular endothelial sprouting model. The pro-angiogenesis effect of the thyroid hormone analogs was blocked by PD 98059, an inhibitor of the mitogen-activated protein kinase (MAPK; ERK1/2) signal transduction cascade. A specific avb3 integrin antagonist (XT199) also inhibited the pro-angiogenesis effect of either thyroid hormone analogs or T4-agarose. Tetrac, a thyroid hormone analog that blocks cell surface-initiated actions of T4 and T3, inhibited the pro-angiogenesis response of thyroid hormone. CONCLUSIONS: T4, T3, and T4-agarose are pro-angiogenic in the three-dimensional human microvascular endothelial sprouting model, an action that is initiated at the plasma membrane, involves avb3 integrin receptors, and is MAPK-dependent.

The thyroid hormone-αvß3 integrin axis in ovarian cancer: regulation of gene transcription and MAPK-dependent proliferation.

Ovarian carcinoma is the fifth common cause of cancer death in women, despite advanced therapeutic approaches. αvß3 integrin, a plasma membrane receptor, binds thyroid hormones (L-thyroxine, T4; 3,5,3'-triiodo-L-thyronine, T3) and is overexpressed in ovarian cancer. We have demonstrated selective binding of fluorescently labeled hormones to αvß3-positive ovarian cancer cells but not to integrin-negative cells. Physiologically relevant T3 (1 nM) and T4 (100 nM) concentrations in OVCAR-3 (high αvß3) and A2780 (low αvß3) cells promoted αv and ß3 transcription in association with basal integrin levels. This transcription was effectively blocked by RGD (Arg-Gly-Asp) peptide and neutralizing αvß3 antibodies, excluding T3-induced ß3 messenger RNA, suggesting subspecialization of T3 and T4 binding to the integrin receptor pocket. We have provided support for extracellular regulated kinase (ERK)-mediated transcriptional regulation of the αv monomer by T3 and of ß3 monomer by both hormones and documented a rapid (30-120 min) and dose-dependent (0.1-1000 nM) ERK activation. OVCAR-3 cells and αvß3-deficient HEK293 cells treated with αvß3 blockers confirmed the requirement for an intact thyroid hormone-integrin interaction in ERK activation. In addition, novel data indicated that T4, but not T3, controls integrin's outside-in signaling by phosphorylating tyrosine 759 in the ß3 subunit. Both hormones induced cell proliferation (cell counts), survival (Annexin-PI), viability (WST-1) and significantly reduced the expression of genes that inhibit cell cycle (p21, p16), promote mitochondrial apoptosis (Nix, PUMA) and tumor suppression (GDF-15, IGFBP-6), particularly in cells with high integrin expression. At last, we have confirmed that hypothyroid environment attenuated ovarian cancer growth using a novel experimental platform that exploited paired euthyroid and severe hypothyroid serum samples from human subjects. To conclude, our data define a critical role for thyroid hormones as potent αvß3-ligands, driving ovarian cancer cell proliferation and suggest that disruption of this axis may present a novel treatment strategy in this aggressive disease.

Metabolism of N-carbobenzoxyl-L-tryptophan by Chromobacterium violaceum.

Chromobacterium violaceum (ATCC 12472) metabolizes N-carbobenzoxyl-L-tryptophan into its 2', 3'-dehydro-derivative, and indole-3-propionic acid into indole-3-acrylic acid. The biotransformation accurs in resting cell incubations, and in growing cultures of the bacterium. Tryptophan in fermentation media enhances the ability of Chromobacterium violaceum to perform the conversion by an undetermined mechanism. The amino acid also prevents stored cultures from losing the ability to accomplish the biotransformation. The reaction apparently requires oxygen, and preliminary experiments suggest that it is catalyzed by a dehydrogenase.

Exclusion of fluid lipid during compression of monolayers of mixtures of dipalmitoylphosphatidylcholine with some other phosphatidylcholines.

Monolayers composed of dipalmitoylphosphatidylcholine and one of four fluid phosphatidylcholines have been studied for their ability to attain low minimum surface tension during compression at two different speeds. The minimum surface tension depended on the compression rate and the proportions of the fluid and rigid lipid in the monolayer. The type of fluid lipid used in the monolayer also affected the minimum surface tension.

Rabbit skeletal muscle sarcoplasmic reticulum Ca(2+)-ATPase activity: stimulation in vitro by thyroid hormone analogues and bipyridines.

Sarcoplasmic reticulum-enriched membranes from rabbit skeletal muscle contained Ca(2+)-ATPase activity which was significantly enhanced (26% increase, P < 0.001) in vitro by physiological concentrations (10(-10) M) of L-thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3). In contrast, the biologically inactive iodothyronine analogues D-T4 and 3,3',5,5'-tetraiodothyroacetic acid (Tetrac) (10(-10) M) were without effect on enzyme activity. 3,5-Dimethyl-3'-isopropyl-L-thyronine (Dimit), a bioactive analogue, was highly effective as a Ca(2+)-ATPase stimulator, increasing enzyme activity by 43% (P < 0.02 vs. T4 effect). A bipyridine cardiac inotropic agent, milrinone, has been reported to be thyromimetic in a myocardial membrane Ca(2+)-ATPase system, and in concentrations from 10(-10) to 10(-5) M enhanced skeletal muscle SR membrane Ca(2+)-ATPase activity in vitro (P < 0.001). Milrinone analogues which have been previously shown to enhance rabbit myocardial membrane Ca(2+)-ATPase activity, and which have a twist relationship of the pyridine rings, were also striated muscle Ca(2+)-ATPase stimulators. We conclude that (1) striated muscle is a mammalian tissue in which physiological levels of biologically relevant thyroid hormone analogues, particularly Dimit, stimulate Ca(2+)-ATPase activity in vitro by a non-genomic mechanism; (2) cardiac bipyridine analogues which are thyromimetic in vitro in rabbit heart, and which have structural homologies with thyroid hormone, are stimulators of rabbit striated muscle sarcoplasmic reticulum Ca(2+)-ATPase activity.

Bilirubin diffusion through lipid membranes.

The possibility that bilirubin can diffuse through lipid bilayers is investigated with liposomes prepared from dipalmitoylphosphatidylcholine (DPPC), egg phosphatidylcholine (egg PC) with 22 mole percent cholesterol, and a lipid extract preparation from N115 neuroblastoma cells. Liposomes were prepared with internalized bilirubin and bovine or human serum albumin, and bilirubin efflux into an exogenous solution of human serum albumin was measured. Efflux from DPPC liposomes was significantly higher above the phase transition temperature than below it. This change was dependent on the lipid undergoing a phase transition and could not be accounted for by 6 K change in temperature. Maximum bilirubin efflux from egg PC-cholesterol liposomes was found to depend on the relative internal and external albumin pools, suggesting an equilibrium distribution of bilirubin between them. These observations demonstrate that bilirubin can diffuse freely through these lipid membranes.

Hexose-specific inhibition in vitro of human red cell Ca(2+)-ATPase activity.

In a concentration-dependent manner (5.5-27.5 mmol/l), D-glucose incubated in vitro with human erythrocyte membranes at 37 degrees C for 1 h inhibited membrane Ca(2+)-ATPase activity by up to 75%. The IC50 was 11 mmol/l. L-Glucose was ineffective, as were 3-O-methylglucose, 2-deoxyglucose, sorbitol and myo-inositol. In contrast, D-fructose decreased Ca(2+)-ATPase activity nearly as effectively as D-glucose and mannose and galactose at 11 mmol/l were less than 50% as effective as D-glucose. Tunicamycin (12 pmol/l), but not 10 mmol/l aminoguanidine, progressively antagonized in vitro the D-glucose effect on the enzyme. Erythrocyte membrane Ca(2+)-ATPase activity may be regulated by glycosylation, rather than nonenzymatic glycation.

Retinoic acid inhibition of thyroxine binding to human transthyretin.

All-trans retinoic acid is a potent inhibitor of [125I]-thyroxine (T4) binding to human erythrocyte membranes and can block the activation by thyroid hormone of erythrocyte Ca(2+)-ATPase [J. Biol. Chem. (1989) 264, 687-689]. In the present studies, retinoic acid was examined for its ability to displace thyroxine from binding sites on human transthyretin (TTR). Scatchard analysis of [125I]T4 binding to purified TTR, determined by equilibrium dialysis, revealed two classes of binding sites with association constants of 3.2 x 10(9) M-1 and 8.1 x 10(6) M-1. All-trans retinoic acid also displaced [125I]T4; 40% of the specifically bound [125I]T4 was displaced at a retinoic acid concentration of 2 x 10(-5) M. Analysis of the high affinity T4 binding site suggests that the Ka for retinoic acid to that site is approx. 10(7) M-1. 8-Anilinonaphthalene-1-sulfonate (ANS), a strongly fluorescing dye, binds to the thyroxine binding sites on TTR. T4 and 3,5,3'-L-triiodothyronine (T3) shifted the fluorescence emission maximum and intensity of an ANS-TTR solution toward the spectrum obtained from uncomplexed ANS. All-trans retinoic acid caused a similar shift in the emission spectrum of ANS, but was less potent than T4. Retinol failed to quench the emission intensity of the ANS-TTR complex, while 13-cis-retinoic acid was less effective than all-trans retinoic acid.

Differential activities of tolbutamide, tolazamide, and glyburide in vitro on rabbit myocardial membrane Ca2+-transporting ATPase activity.

At clinically achievable concentrations (10(-9) to 5 X 10(-6) M), tolbutamide and tolazamide are in vitro inhibitors of Ca2+-transporting ATPase activity in sarcolemma-enriched rabbit myocardial membranes (sulfonylurea IC50, 10(-7) M). Thyroid hormone stimulation of this calcium pump-associated enzyme in vitro has been previously reported; in our study, this hormonal action was shown to be inhibited by tolbutamide and tolazamide. In contrast to these two sulfonylureas, glyburide (up to 5 X 10(-6) M) had no effect on basal or thyroid hormone-stimulable Ca2+-ATPase activity in vitro. Studies of binding of radiolabeled purified calmodulin to heart membranes showed that tolbutamide and tolazamide inhibited this interaction, whereas glyburide had no effect on calmodulin binding. Addition of purified calmodulin (5-40 ng/micrograms membrane protein) to myocardial membranes incubated with 10(-7) M tolbutamide or tolazamide restored Ca2+-ATPase activity and thyroid hormone responsiveness of the enzyme. Inhibition by tolbutamide and tolazamide of myocardial sarcolemmal Ca2+-ATPase is a mechanism by which these two sulfonylureas may at least transiently raise resting sarcoplasmic Ca2+ concentration. This effect of sulfonylureas on Ca2+-ATPase is not expressed in the presence of the benzamide side chain of glyburide. The inhibitory action of certain sulfonylureas on Ca2+-ATPase is mediated by interference of the agents with the binding of calmodulin to cardiac membranes.

The effect of in vivo glucose administration on human erythrocyte Ca2+-ATPase activity and on enzyme responsiveness in vitro to thyroid hormone and calmodulin.

To characterize endogenous control mechanisms for human erythrocyte membrane Ca2+-ATPase ("calcium pump") activity, we studied the effect of changes in blood glucose concentration in vivo within the physiologic range on Ca2+-ATPase activity in red cells. Red cells obtained in the course of induced hyperglycemia were also studied to determine susceptibility of membrane Ca2+-ATPase to stimulation in vitro by thyroid hormone and calmodulin, both of which have been shown previously to enhance Ca2+-ATPase activity. Oral glucose administration (75 g) to eight healthy, adult subjects induced predictable increases in concentrations of blood glucose and immunoreactive insulin. Basal levels of activity of Ca2+-ATPase in red cells obtained after glucose ingestion fell 55% (P less than 0.025) by 30 min after glucose with recovery of enzyme activity to levels not significantly different from basal by 60 min. Activity of red cell Ca2+-ATPase at time zero was significantly stimulated in vitro by thyroxine (T4, 10(-10) M), triiodo-L-thyronine (T3, 10(-10) M), and calmodulin (100 ng/mg membrane protein). In vivo glucose administration led to depression of red cell enzyme responsiveness in vitro to T4 and T3; recovery from this effect did not occur by 120 min after oral administration of glucose. Calmodulin responsiveness of the enzyme in vitro was less significantly reduced in red cells obtained after glucose ingestion. Intravenous (i.v.) glucose administration (20 g) to five subjects also led to decreased basal enzyme activity (61% of fasting level at 20 min). A significant decrease in response of enzyme to T4 was achieved by 8 min after glucose administration (P less than 0.02), with recovery by 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

The alpha 1-adrenergic receptor in human erythrocyte membranes mediates interaction in vitro of epinephrine and thyroid hormone at the membrane Ca(2+)-ATPase.

Membrane Ca(2+)-ATPase activity was stimulated in vitro separately by T4 (10(-10) M) and by epinephrine (10(-6) M). In the presence of a fixed concentration of T4, additions of 10(-8) and 10(-6) M epinephrine reduced the T4 effect on the enzyme. beta-Adrenergic blockade with propranolol (10(-6) M) prevented stimulation by epinephrine of Ca(2+)-ATPase activity, but did not prevent the suppressive action of epinephrine on T4-stimulable Ca(2+)-ATPase. In contrast, alpha 1-adrenergic blockade with unlabelled prazosin restored the effect of T4 on Ca(2+)-ATPase activity in the presence of epinephrine. Like propranolol, prazosin prevented enhancement of enzyme activity by epinephrine in the absence of thyroid hormone. Neither prazosin nor propranolol had any effect on the stimulation by T4 of red cell Ca(2+)-ATPase in the absence of epinephrine. Analysis of radiolabelled prazosin binding to human red cell membranes revealed the presence of a single class of high-affinity binding sites (Kd, 1.2 x 10(-8) M; Bmax, 847 fmol/mg membrane protein). Thus, the human erythrocyte membrane contains alpha 1-adrenergic receptor sites that are capable of regulating Ca(2+)-ATPase activity.