Intercompartmental Distribution Research Articles

TMX5/TXNDC15, a natural trapping mutant of the PDI family is a client of the proteostatic factor ERp44.

The ER is the organelle of nucleated cells that produces lipids, sugars, and proteins. More than 20 ER-resident members of the protein disulfide isomerase (PDI) family regulate formation, isomerization, and disassembly of covalent bonds in newly synthesized polypeptides. The PDI family includes few membrane-bound members. Among these, TMX1, TMX2, TMX3, TMX4, and TMX5 belong to the thioredoxin-related transmembrane (TMX) protein family. TMX5 is the least-known member of the family. Here, we establish that TMX5 covalently engages via its active site cysteine residue at position 220 a subset of secretory proteins, mainly single- and multipass Golgi-resident polypeptides. TMX5 also interacts non-covalently, and covalently, via non-catalytic cysteine residues, with the PDI family members PDI, ERp57, and ERp44. The association between TMX5 and ERp44 requires formation of a mixed disulfide between the catalytic cysteine residue 29 of ERp44 and the non-catalytic cysteine residues 114 and/or 124 of TMX5 and controls the ER localization of TMX5 in pre-Golgi compartments. Thus, TMX5 belongs to the family of proteins including Ero1α, Ero1β, Prx4, ERAP1, and SUMF1 that operate in pre-Golgi compartments but lack localization sequences required to position themselves and rely on ERp44 engagement for proper intercompartmental distribution.

Population pharmacokinetics of dexamethasone in critically ill COVID-19 patients: Does inflammation play a role?

PurposeThe aim of this study is to design a population pharmacokinetic study to gain a deeper understanding of the pharmacokinetics of dexamethasone in critically ill COVID-19 patients in order to identify relevant covariates that can be used to personalize dosing regimens. MethodsBlood samples from critically ill patients receiving fixed-dose intravenous dexamethasone (6 mg/day) for the treatment of COVID-19 were sampled in a retrospective pilot study. The data were analyzed using Nonlinear Mixed Effects Modeling (NONMEM) software for population pharmacokinetic analysis and clinically relevant covariates were selected and evaluated. ResultsA total of 51 dexamethasone samples from 18 patients were analyzed and a two-compartment model fit the data best. The mean population estimates were 2.85 L/h (inter-individual-variability 62.9%) for clearance, 15.4 L for the central volume of distribution, 12.3 L for the peripheral volume of distribution and 2.1 L/h for the inter-compartmental distribution clearance. The covariate analysis showed a significant negative correlation between dexamethasone clearance and CRP. ConclusionsDexamethasone PK parameters in ICU COVID patients were substantially different from those from non-ICU non-COVID patients, and inflammation may play an important role in dexamethasone exposure. This finding suggests that fixed-dose dexamethasone over several days may not be appropriate for ICU COVID patients.

Analysis of Complex Absorption After Multiple Dosing: Application to the Interaction Between the P-glycoprotein Substrate Talinolol and Rifampicin

PurposeIn order to clarify the effect of rifampicin on the bioavailability of the P-glycoprotein substrate talinolol, its absorption kinetics was modeled after multiple-dose oral administration of talinolol in healthy subjects.MethodsA sum of two inverse Gaussian functions was used to calculate the time course of the input rate into the systemic circulation.ResultsThe estimated rate of drug entry into the systemic circulation revealed two distinct peaks at 1 and 3.5 h after administration. Rifampicin did not affect bioavailability of talinolol, but did shift the second peak of the input function by 1.3 h to later times. Elimination clearance and one of the intercompartmental distribution clearances increased significantly under rifampicin treatment.ConclusionsRifampicin changes the time course of absorption rate but not the fraction absorbed of talinolol. The model suggests the existence of two intestinal absorption windows for talinolol.

Population pharmacokinetics of unbound ceftriaxone in a critically ill population.

To develop a reliable 2-compartment population pharmacokinetic (PK) model for unbound ceftriaxone in a critically ill population and determine an optimal dosing regimen. This was a prospective, single-center, observational study of critically ill patients treated with ceftriaxone. Unbound serum ceftriaxone concentrations were measured using validated ultrafiltration and ultra-performance liquid chromatography-tandem mass spectrometry. PK analysis and dosing simulations were performed using an iterative 2-stage Bayesian fitting procedure and Monte Carlo simulations. The PK/pharmacodynamics (PD) target was attained when unbound serum ceftriaxone concentrations exceeded 4 times the minimum inhibitory concentration (MIC) for ≥60% of the dosing interval (ƒT>4xMIC ≥ 60%). 91 patients were enrolled, and 173 unbound ceftriaxone concentrations were acquired. The population PK parameter estimates were hepatic clearance 5.2±0.9L/h/1.85m2, the unbound renal clearance of ceftriaxone divided by the creatinine clearance 0.61±0.24, lean body mass corrected volume of distribution of the central compartment 0.82±0.21L/kg, and intercompartmental distribution rate constant from central to peripheral compartment 0.18±0.08h-1. Dosing simulations predicted ƒT>4 mg/L of 88% (95% CI: 69-100%) for 2,000 mg ceftriaxone once daily and ƒT>4 mg/L of 100% (95% CI: 100-100%) both for 1,000 mg twice daily and continuous infusion of 2,000 mg daily. We developed a reliable population PK model for unbound ceftriaxone in a critically ill population. Dosing simulations revealed ƒT>4 mg/L ≥60% for 1,000mg twice daily and 2,000 mg once daily or by continuous infusion.

Clinical Pharmacokinetic Assessment of Kratom (Mitragyna speciosa), a Botanical Product with Opioid-like Effects, in Healthy Adult Participants.

Increasing use of the botanical kratom to self-manage opioid withdrawal and pain has led to increased kratom-linked overdose deaths. Despite these serious safety concerns, rigorous fundamental pharmacokinetic knowledge of kratom in humans remains lacking. We assessed the pharmacokinetics of a single low dose (2 g) of a well-characterized kratom product administered orally to six healthy participants. Median concentration-time profiles for the kratom alkaloids examined were best described by a two-compartment model with central elimination. Pronounced pharmacokinetic differences between alkaloids with the 3S configuration (mitragynine, speciogynine, paynantheine) and alkaloids with the 3R configuration (mitraciliatine, speciociliatine, isopaynantheine) were attributed to differences in apparent intercompartmental distribution clearance, volumes of distribution, and clearance. Based on noncompartmental analysis of individual concentration-time profiles, the 3S alkaloids exhibited a shorter median time to maximum concentration (1–2 vs. 2.5–4.5 h), lower area under the plasma concentration-time curve (430–490 vs. 794–5120 nM × h), longer terminal half-life (24–45 vs. ~12–18 h), and higher apparent volume of distribution during the terminal phase (960–12,700 vs. ~46–130 L) compared to the 3R alkaloids. Follow-up mechanistic in vitro studies suggested differential hepatic/intestinal metabolism, plasma protein binding, blood-to-plasma partitioning, and/or distribution coefficients may explain the pharmacokinetic differences between the two alkaloid types. This first comprehensive pharmacokinetic characterization of kratom alkaloids in humans provides the foundation for further research to establish safety and effectiveness of this emerging botanical product.

An Interactive Jupyter Notebook for Teaching the Foundational Mathematical Basis of Compartmental Pharmacokinetics

Pharmacokinetics is often taught as two different lessons, the foundational mathematical basis and the clinical application. Due to the lack of hands-on exercises, pharmacokinetics can be difficult to teach and students report struggling with the topic. Therefore, I have developed an interactive Jupyter notebook that demonstrates the mathematical basis behind one- and two-compartment pharmacokinetic models. This notebook uses a combination of “markup” cells, which display relevant equations and text, and “code” cells, which hold Python code that executes, models, and graphs the various pharmacokinetic equations. Students benefit from exposure to this aspect of computer science because the code remains visible. With the code pre-written, students are able to see the implementations of programming in drug pharmacokinetic modeling without having to construct the code themselves. This notebook includes both the differential and algebraic versions of one- and two- compartment models. The code also generates interactive graphs where students can use sliders for each parameter (half-life, inter-compartmental distribution rates, and dose of drug) to explore the effects of the equations parameters on the output of drug concentration over time. The conversion between macro constants and micro constants is also demonstrated and explained. All software used is freely available, so students can download the notebook onto their personal computers. No computer science experience is needed to execute this tool. However, instructors can easily adapt the notebook to their particular needs, adding or removing cells as desired. I successfully used this notebook in my undergraduate upper-division biology elective, “Foundations of Pharmacology”, and in a guest lectured Master's level course on the practical application of pharmacokinetics. Overall, this tool will be useful for teaching the mathematical basis of basic pharmacokinetics while allowing students to gain useful exposure to computer data science.

Population Pharmacokinetics of Alemtuzumab (Campath) in Pediatric Hematopoietic Cell Transplantation: Towards Individualized Dosing to Improve Outcome.

Background and ObjectiveAlemtuzumab (Campath®) is used to prevent graft-versus-host disease and graft failure following pediatric allogeneic hematopoietic cell transplantation. The main toxicity includes delayed immune reconstitution, subsequent viral reactivations, and leukemia relapse. Exposure to alemtuzumab is highly variable upon empirical milligram/kilogram dosing.MethodsA population pharmacokinetic (PK) model for alemtuzumab was developed based on a total of 1146 concentration samples from 206 patients, aged 0.2–19 years, receiving a cumulative intravenous dose of 0.2–1.5 mg/kg, and treated between 2003 and 2015 in two centers.ResultsAlemtuzumab PK were best described using a two-compartment model with a parallel saturable and linear elimination pathway. The linear clearance pathway, central volume of distribution, and intercompartmental distribution increased with body weight. Blood lymphocyte counts, a potential substrate for alemtuzumab, did not impact clearance.ConclusionThe current practice with uniform milligram/kilogram doses leads to highly variable exposures in children due to the non-linear relationship between body weight and alemtuzumab PK. This model may be used for individualized dosing of alemtuzumab.Electronic supplementary materialThe online version of this article (10.1007/s40262-019-00782-0) contains supplementary material, which is available to authorized users.

Mechanistic insights into the role of prenyl-binding protein PrBP/\u03b4 in membrane dissociation of phosphodiesterase 6

Isoprenylated proteins are associated with membranes and their inter-compartmental distribution is regulated by solubilization factors, which incorporate lipid moieties in hydrophobic cavities and thereby facilitate free diffusion during trafficking. Here we report the crystal structure of a solubilization factor, the prenyl-binding protein (PrBP/δ), at 1.81 Å resolution in its ligand-free apo-form. Apo-PrBP/δ harbors a preshaped, deep hydrophobic cavity, capacitating apo-PrBP/δ to readily bind its prenylated cargo. To investigate the molecular mechanism of cargo solubilization we analyzed the PrBP/δ-induced membrane dissociation of rod photoreceptor phosphodiesterase (PDE6). The results suggest that PrBP/δ exclusively interacts with the soluble fraction of PDE6. Depletion of soluble species in turn leads to dissociation of membrane-bound PDE6, as both are in equilibrium. This “solubilization by depletion” mechanism of PrBP/δ differs from the extraction of prenylated proteins by the similar folded solubilization factor RhoGDI, which interacts with membrane bound cargo via an N-terminal structural element lacking in PrBP/δ.

Simultaneous Semimechanistic Population Analyses of Levofloxacin in Plasma, Lung, and Prostate To Describe the Influence of Efflux Transporters on Drug Distribution following Intravenous and Intratracheal Administration.

Levofloxacin (LEV) is a broad-spectrum fluoroquinolone used to treat pneumonia, urinary tract infections, chronic bacterial bronchitis, and prostatitis. Efflux transporters, primarily P-glycoprotein (P-gp), are involved in LEV's tissue penetration. In the present work, LEV free lung and prostate interstitial space fluid (ISF) concentrations were evaluated by microdialysis in Wistar rats after intravenous (i.v.) and intratracheal (i.t.) administration (7 mg/kg of body weight) with and without coadministration of the P-gp inhibitor tariquidar (TAR; 15 mg/kg administered i.v.). Plasma and tissue concentration/time profiles were evaluated by noncompartmental analysis (NCA) and population pharmacokinetics (popPK) analysis. The NCA showed significant differences in bioavailability (F) for the control group (0.4) and the TAR group (0.86) after i.t. administration. A four-compartment model simultaneously characterized total plasma and free lung (compartment 2) and prostate (compartment 3) ISF concentrations. Statistically significant differences in lung and prostate average ISF concentrations and levels of kidney active secretion in the TAR group from those measured for the control group (LEV alone) were observed. The estimated population means were as follows: volume of the central compartment (V1), 0.321 liters; total plasma clearance (CL), 0.220 liters/h; TAR plasma clearance (CLTAR), 0.180 liters/h. The intercompartmental distribution rate constants (K values) were as follows: K12, 8.826 h(-1); K21, 7.271 h(-1); K13, 0.047 h(-1); K31, 7.738 h(-1); K14, 0.908 h(-1); K41, 0.409 h(-1); K21 lung TAR (K21LTAR), 8.883 h(-1); K31 prostate TAR (K31PTAR), 4.377 h(-1). The presence of P-gp considerably impacted the active renal secretion of LEV but had only a minor impact on the efflux from the lung following intratracheal dosing. Our results strongly support the idea of a role of efflux transporters other than P-gp contributing to LEV's tissue penetration into the prostrate.

Vitamin B-6 vitamers in human plasma and cerebrospinal fluid

Vitamin B-6 comprises a group of 6 interrelated vitamers and is essential for numerous physiologic processes, including brain functioning. Genetic disorders disrupting vitamin B-6 metabolism have severe clinical consequences. To adequately diagnose known and novel disorders in vitamin B-6 metabolism, a reference set is required containing information on all vitamin B-6 vitamers in plasma and cerebrospinal fluid (CSF). Concentrations of vitamin B-6 vitamers in the plasma and CSF of 533 adult subjects were measured by ultra high-performance liquid chromatography-tandem mass spectrometry. The relative vitamin B-6 vitamer composition of plasma [pyridoxal phosphate (PLP) > pyridoxic acid (PA) > pyridoxal] differed from that of CSF (pyridoxal > PLP > PA > pyridoxamine). Sex influenced vitamin B-6 vitamer concentrations in plasma and CSF and should therefore be taken into account when interpreting vitamin B-6 vitamer concentrations. The strict ratios and strong correlations between vitamin B-6 vitamers point to a tight regulation of vitamin B-6 vitamer concentrations in blood and CSF. Given the unique design of this study, with simultaneously withdrawn blood and CSF from a large number of subjects, reliable CSF:plasma ratios and correlations of vitamin B-6 vitamers could be established. We provide an extensive reference set of vitamin B-6 vitamer concentrations in plasma and CSF. In addition to providing insight on the regulation of individual vitamers and their intercompartmental distribution, we anticipate that these data will prove to be a valuable reference set for the diagnosis and treatment of conditions associated with altered vitamin B-6 metabolism.

Abstract 3224: Preclinical PKPD modeling and human dose projection of PF-04691502, a PI3K/mTOR dual inhibitor

Abstract PF-04691502 is a potent dual inhibitor of PI3K and mTOR, which are involved in regulating cell growth, proliferation and survival. The main objective of this work was to develop a preclinical pharmacokinetic-pharmacodynamic (PKPD) model for the compound and project the human efficacious dose. The PK of PF-04691502 in mouse obtained following oral dosing was described by a linear 2-compartment model which was used to drive two separate PD models: 1) an exponential growth model describing the tumor growth inhibition (TGI) and 2) an indirect-response model describing changes in intratumoral pAKT-S473/AKT in the U87MG xenograft mouse model. Based on the PK model, the half-life calculated from the linear elimination constant (k = 0.306 hr−1) was 2.3 hr and the plasma-compartment volume of distribution was 8.72 L/kg. The inter-compartmental distribution rate constants were 0.282 hr−1 and 0.212 hr−1 for k12 and k21, respectively. The model estimated in-vivo potency (IC50) for pAKT-S473/AKT suppression was 38.3 nM which was within the range of the IC50 (23 nM) for TGI (as parameterized by the model). The Imax estimated from the model was 0.975 (or 97.5%), which indicated nearly complete suppression of pAKT-S473/AKT production rate by PF-04691502. Based on the PKPD model and the scaled human PK, a clinical dose of 10 mg QD was determined to be adequate for maintaining the level of pAKT-S473/AKT below 50% of baseline. At steady-state PK this dose yielded a range of 50-80% human pAKT-S473/AKT suppression over the 24 hr dosing interval. In conclusion, PF-04691502 was determined to have a robust PKPD relationship in the preclinical animal model and was projected to have a clinically achievable efficacious dose of approximately 10 mg QD. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3224.

Population Volume Kinetics Predicts Retention of 0.9% Saline Infused in Awake and Isoflurane-anesthetized Volunteers

In previous work, extravascular expansion was observed to be enhanced by isoflurane anesthesia in sheep when a crystalloid bolus was administered. The aim of the current study was to further elaborate these investigations to humans and to explore the use of population kinetics in the analysis of fluid shifts. Eleven healthy volunteers participated in two experiments each, either awake or isoflurane anesthetized, during which they received 25 ml/kg saline, 0.9%, intravenously over 20 min. Plasma dilution data were derived from repeated sampling of hemoglobin concentration, and population pharmacokinetic analysis was conducted using the WinNonMix 2.0.1 software (Pharsight Corporation, Mountain View, CA). Plasma hormones were measured, and hemodynamic values were monitored. Fluid infusion during isoflurane anesthesia was followed by a higher cardiac output, lower arterial pressure, and lower urinary excretion as compared with the awake protocol (P < 0.05). Albumin dilution was greater than hemoglobin concentration-derived plasma dilution, which indicates a transcapillary leak of albumin. A two-compartment model with an isoflurane-depressed, intercompartmental distribution parameter predicted that more than 50% of the infused volume was retained in the peripheral compartment at 180 min in both protocols. Isoflurane markedly increased the plasma levels of renin and aldosterone, whereas vasopressin was mostly unchanged. Fluid retention after rapid infusion of 0.9% saline was prominent in both awake and isoflurane-anesthetized subjects. Altered kinetics of infused 0.9% saline during isoflurane anesthesia was expressed as reduced clearance and a slower distribution, resulting in a small but significant increase in fluid accumulation in the body fluid compartments. These changes may be due to the associated decreasing of mean arterial pressure and increased release of renin and aldosterone.

Pharmacokinetic analysis

Pharmacokinetic analysis provides information on the distribution and elimination of a drug and facilitates the formulation of optimum dosing guidelines. Following the administration of a known amount of drug, blood samples are collected at timed intervals. Drug concentration data are then plotted on a logarithmic scale against time. The curve initially falls steeply as drug distributes from blood to tissues. Thereafter, the slope of the second phase represents the rate of removal of drug from the body. The intercepts of the different phases on the y axis and their slopes can be determined graphically or with the aid of computer analysis. For most drugs, the elimination profile can be modelled by two or three exponential terms, with the best fit indicating whether a two or three compartment model is preferred. From the intercepts A and B and the slopes alpha and beta, compartment model parameters (V1, k10, k12 and k21) can be determined. V1 (ml/kg) represents the volume of the central compartment, k10 (per minute) the elimination rate constant from the central compartment, and k12 and k21 inter-compartmental distribution rate constants. Drug clearance (ml/min/kg) is the product of k10 and V1. In determining drug dosage, the peak concentration (microg/ml) after a bolus dose is determined by the dose administered (microg/kg) divided by V1 (ml/kg). Clearance is of greater importance in determining the rate of infusion required to maintain a desired drug concentration. Computer simulation programs are now available and can be used to explore the influence of changes in pharmacokinetic parameters on drug behaviour. This article highlights some of these programs and provides illustrations of simulations of the behaviour of propofol and lidocaine.

Within- and between-subject variations in pharmacokinetic parameters of ethanol by analysis of breath, venous blood and urine.

To evaluate the prerequisites for using ethanol dilution to estimate total body water, we studied the within- and between-subject variation in the parameter estimates of a two-compartment model for ethanol pharmacokinetics with parallel Michaelis-Menten and first-order renal elimination. Because sampling of breath might be preferable in some clinical situations the parameter estimates derived from breath and venous blood were compared. On two occasions, ethanol 0.4 g kg-1 was given by intravenous infusion to 16 volunteers after they had fasted overnight. The proposed model was fitted by means of nonlinear regression to concentration-time data measured in the breath, venous blood and urine during 360 min. The model contained six parameters: Vmax and Km (Michaelis-Menten elimination constants), CLd (intercompartmental distribution parameter), VC and VT (volumes of the central and tissue compartment, respectively) and CLR (renal clearance). The volume of distribution, Vss, was calculated as the sum of VC and VT. The mean +/- total s.d. of the parameter estimates derived from blood data were Vmax 95 +/- 25 mg min-1, Km 27 +/- 19 mg l-1, CLd 809 +/- 232 ml min-1, VC 14.5 +/- 4.3 l, VT 21. 2 +/- 4.4 l, CLR 3.6 +/- 2.0 ml min-1 and Vss 35.8 +/- 4.3 l. The variation within subjects amounted to 3%, 9%, 21%, 21%, 17%, 26% and 2%, respectively, of the total variation. Breath samples were associated with a similar or lower variation than blood, both within and between subjects. About 1.5% of the infused ethanol was recovered in the urine. The low within-subject variation of the key parameter Vss (only 2%) suggests that ethanol dilution analysed by the pharmacokinetic model applied here may be used as an index of the total body water. Breath samples yielded at least as good reproducibility in the model parameters as venous blood.

Alcuronium

Alcuronium may be considered a muscle relaxant of historical rather than clinical significance.However, recent information from the manufacturer revealed its persisting clinical use in 26 countries worldwide. Thus, a pharmacodynamic-pharmacokinetic update appears mandatory. An intravenous (IV) single-bolus injection of alcuronium (0.25 mg/kg = ED95) was administered to 10 patients undergoing maxillofacial surgery during nitrous-oxide opioid anesthesia. Alcuronium neuromuscular block (evoked twitch tension), plasma concentration, and renal elimination (high-performance liquid chromatography [HPLC] assay) were measured during the 12-h after its administration. The time of onset, the time from end of injection to recovery to 25% of control twitch tension (DUR25%), and the recovery index were 2.2 +/- 1.2, 54 +/- 14, and 37 +/- 11 min, respectively (mean +/- SD). Two hours after the injection of alcuronium, partial recovery from the neuromuscular block had occurred from 100% to 26% +/- 24% depression of twitch tension, although less than 25% of the injected dose was recovered from the urine. The 12-h plasma concentration and urinary recovery were 0.1 +/- 0.08 mg/L (one-sixth of the 50% inhibitory concentration) and 61% +/- 20%, respectively. Recovery from neuromuscular block was dominated by intercompartmental distribution rather than by renal elimination. Since alcuronium does not undergo biodegradation, our data may serve as a reference for the complex pharmacokinetics of readily metabolized modern muscle relaxants. The long plasma half-life with slow excretion merits attention with respect to the erroneous original perception that alcuronium was an intermediate-acting muscle relaxant. (Anesth Analg 1995;80:373-7)

Alcuronium: a pharmacodynamic and pharmacokinetic update.

Alcuronium may be considered a muscle relaxant of historical rather than clinical significance. However, recent information from the manufacturer revealed its persisting clinical use in 26 countries worldwide. Thus, a pharmacodynamic-pharmacokinetic update appears mandatory. An intravenous (IV) single-bolus injection of alcuronium (0.25 mg/kg = ED95) was administered to 10 patients undergoing maxillofacial surgery during nitrous-oxide opioid anesthesia. Alcuronium neuromuscular block (evoked twitch tension), plasma concentration, and renal elimination (high-performance liquid chromatography [HPLC] assay) were measured during the 12-h after its administration. The time of onset, the time from end of injection to recovery to 25% of control twitch tension (DUR25%), and the recovery index were 2.2 +/- 1.2, 54 +/- 14, and 37 +/- 11 min, respectively (mean +/- SD). Two hours after the injection of alcuronium, partial recovery from the neuromuscular block had occurred from 100% to 26% +/- 24% depression of twitch tension, although less than 25% of the injected dose was recovered from the urine. The 12-h plasma concentration and urinary recovery were 0.1 +/- 0.08 mg/L (one-sixth of the 50% inhibitory concentration) and 61% +/- 20%, respectively. Recovery from neuromuscular block was dominated by intercompartmental distribution rather than by renal elimination. Since alcuronium does not undergo biodegradation, our data may serv as a reference for the complex pharmacokinetics of readily metabolized modern muscle relaxants. The long plasma half-life with slow excretion merits attention with respect to the erroneous original perception that alcuronium was an intermediate-acting muscle relaxant.

The appearance, distribution, and longevity of receptor-[125I]T3 complexes within the nuclei of isolated rat hepatocytes.

The nuclei of isolated rat hepatocytes were separable into three receptor compartments based upon their differential salt extractabilities: nucleoplasmic receptors (NP) extractable with 0.15 M KCl, high-salt extractable receptors (HSE) extractable with 0.4 M KCl, and salt-resistant receptors (SR) extractable with 0.4 M KCl/5 mM dithiothreitol. The receptor distribution among the three compartments was approximately NP, 45%; HSE, 30%; SR, 25%. The mean percent occupancy with endogenous T3 of the SR receptors (86%) was higher than the occupancies of the NP receptors (68%) and the HSE receptors (63%). When hepatocytes were pulsed with 3 nM [125I]T3 at 37 degrees C for brief intervals, receptor-[125I]T3 complexes were detectable in all three nuclear compartments within 15 sec. With increasing pulse intervals up to 120 sec, the receptor content of each nuclear compartment increased progressively and without evidence of preferential accumulation in any of the three compartments. To determine the life span and intercompartmental "migration" pattern of nuclear receptors, hepatocytes were pulsed with 3 nM [125I]T3 at 37 degrees C for 2.5 min or 5 min, followed by a chase with a 500-fold excess of nonlabeled T3. The population of receptor-[125I]T3 complexes generated during the pulse was serially recovered at increasing intervals after the chase. The complexes of each compartment dissociated with a half-life of approximately 3 min and manifested no predilection to accumulate in any of the compartments. Exposure of isolated hepatocytes to 3 nM T3 for 5 min or 10 min at 37 degrees C induced no change in the gross intercompartmental distribution of receptors compared to control hepatocytes incubated without T3.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental study of flow distribution features in the electrodialyzer

The liquid distribution to the intercompartments in an electrodialyzer (ED) has been measured. Theoretical distribution coincided basically with determined results is obtained. The flow pattern in contributor and collector, which are mainly composed of internal conduits i.e., all the holes in alternately places gaskets and membranes, is shown to be a flowing model where the friction term dominates. Some suggestions are presented to deal with the intercompartmental distribution of nonuniform, in which significant predictions can be made for the ED design.

Organ invasion and the kinetics of intercompartmental distribution in the BN myelocytic leukaemia

B~rDV.S cellular kinetics of proliferation, the patterns of organ invasion and the kinetics of the distribution of leukaemic cells between various functional compartments are highly relevant to obtain insight into the general growth characteristics of leukaemia. In the BN acute myelocytic leukaemia, organ invasion was studied by histological follow-up of various organs during leukaemia development. The kinetics of the distribution were determined by means of tracing infused labelled leukaemic cells in the blood and in the organs.