Search PubMed⌕ Search

Biomedical subjects

C S Patlak

Publications and source records attributed to C S Patlak.

104 records · Page 6Linked to original sources
PubMed1974

Osmosis in cortical collecting tubules. A theoretical and experimental analysis of the osmotic transient phenomenon.

This paper reports a theoretical analysis of osmotic transients and an experimental evaluation both of rapid time resolution of lumen to bath osmosis and of bidirectional steady-state osmosis in isolated rabbit cortical collecting tubules exposed to antidiuretic hormone (ADH). For the case of a membrane in series with unstirred layers, there may be considerable differences between initial and steady-state osmotic flows (i.e., the osmotic transient phenomenon), because the solute concentrations at the interfaces between membrane and unstirred layers may vary with time. A numerical solution of the equation of continuity provided a means for computing these time-dependent values, and, accordingly, the variation of osmotic flow with time for a given set of parameters including: P(f) (cm s(-1)), the osmotic water permeability coefficient, the bulk phase solute concentrations, the unstirred layer thickness on either side of the membrane, and the fractional areas available for volume flow in the unstirred layers. The analyses provide a quantitative frame of reference for evaluating osmotic transients observed in epithelia in series with asymmetrical unstirred layers and indicate that, for such epithelia, P(f) determinations from steady-state osmotic flows may result in gross underestimates of osmotic water permeability. In earlier studies, we suggested that the discrepancy between the ADH-dependent values of P(f) and P(DDw) (cm s(-1), diffusional water permeability coefficient) was the consequence of cellular constraints to diffusion. In the present experiments, no transients were detectable 20-30 s after initiating ADH-dependent lumen to bath osmosis; and steady-state ADH-dependent osmotic flows from bath to lumen and lumen to bath were linear and symmetrical. An evaluation of these data in terms of the analytical model indicates: First, cellular constraints to diffusion in cortical collecting tubules could be rationalized in terms of a 25-fold reduction in the area of the cell layer available for water transport, possibly due in part to transcellular shunting of osmotic flow; and second, such cellular constraints resulted in relatively small, approximately 15%, underestimates of P(f).

Animals↗
PubMed1972

A compartmental analysis of 24 Na kinetics in rat cerebrum, sciatic nerve and cerebrospinal fluid.

1. The kinetics of (24)Na exchange in rat cerebrospinal fluid, brain and sciatic nerve were studied during steady-state plasma isotope conditions. The entrance of (24)Na into brain and sciatic nerve was found to fit a three compartmental model. Using newly derived equations for compartmental analysis, the first compartment (24)Na space of brain was found to be about 22% and the second compartment space about 6%; the corresponding sciatic nerve spaces were 26 and 11%, respectively. In the discussion, arguments are presented that suggest that the first compartment is the extracellular space (ECS) and the second compartment is the intracellular space. The t((1/2)) for compartmental equilibration between plasma and brain ECS was 2 hr and from ECS to intracellular space 14 hr; in nerve the respective t((1/2))'s were (2/3) hr and 10 hr.2. A third compartment of 18% was found in sciatic nerve which was interpreted to be anatomically confined to the epi- and perineurium; in brain the corresponding space was 2% and was felt to be anatomically and kinetically an inactive closed compartment in parallel with the blood.3. There were two t((1/2))'s for plasma-c.s.f. (24)Na equilibration of less than 10 min and 2 hr.4. Profiles of brain, from cortex to ventricle, at 6 min, demonstrated a gradient of decreasing (24)Na radioactivity from ventricle to cortex.

Animals↗
PubMed1971

Theoretical analysis of net tracer flux due to volume circulation in a membrane with pores of different sizes. Relation to solute drag model.

When osmotic pressure across an artificial membrane, produced by a permeable electrically neutral solute on one side of it, is balanced by an external pressure difference so that there is no net volume flow across the membrane, it has been found that there will be a net flux of a second electrically neutral tracer solute, present at equal concentrations on either side of the membrane, in the direction that the "osmotic" solute diffuses. This has been ascribed to solute-solute interaction or drag between the tracer and the osmotic solutes. An alternative model, presented here, considers the membrane to have pores of different sizes. Under general assumptions, this "heteroporous" model will account for both the direction of net tracer flux and the observed linear dependence of unidirectional tracer fluxes on the concentration of the osmotic solute. The expressions for the fluxes of solutes and solvent are mathematically identical under the two models. An inequality is derived which must be valid if the solute interaction model and/or the heteroporous model can account for the data. If the inequality does not hold, then the heteroporous model alone cannot explain the data. It was found that the inequality holds for most published observations except when dextran is the osmotic solute.

Cell Membrane Permeability↗
PubMedDate not supplied

Correlations between plasminogen activator inhibitor-1 and peritoneal transport in pediatric CCPD patients.

OBJECTIVE: Plasminogen activator inhibitor-1 (PAI-1) is an important regulator of plasminogen activators and has been shown to be involved in the accumulation of extracellular matrix (ECM) in various tissues. Since peritoneal ECM is a resistance site for peritoneal transport, the production and release of PAI-1 in the peritoneum may affect the peritoneal transport of water and small solutes. DESIGN: The linear correlations between the dialysate PAI-1 levels and the variables of peritoneal transport during peritoneal equilibration tests (PET) were examined. SETTING: A tertiary university hospital. PATIENTS: Six stable pediatric patients (age 10.8 +/- 4 years) undergoing continuous cycler-assisted peritoneal dialysis were included. INTERVENTIONS: None. RESULTS: All data are mean +/- SD. There was a positive correlation between the infused volume and the net ultrafiltration (UF, 198 +/- 127 mL, r = 0.82, p < 0.05). The dialysate PAI-1 levels increased during the dwell time (2.44 +/- 2.23 ng/mL or 2.46 +/- 1.72 micrograms at 4 hours vs 0.04 +/- 0.1 ng/mL or 0.04 +/- 0.09 micrograms at 0 hour, p < 0.05). The saturation indices (dialysate/plasma ratio) of PAI-1 and albumin at 4 hours were 1.05 +/- 1.21 and 0.028 +/- 0.004, respectively. The changes from 0 hour dwell to 4 hour dwell in the dialysate PAI-1 concentration (PAI4-0, 2.4 +/- 2.2 ng/mL) or amount corrected to body surface area (APAI4-0/BSA, 2.61 +/- 2.11 micrograms/m2) negatively correlated with UF or UF/body surface area and positively correlated with the number of episodes of peritonitis. There was no correlation between PAI4-0,APAI4-0/BSA, or plasma PAI-1 concentration and the mass transfer coefficient and clearance of either urea or creatinine. CONCLUSIONS: The elevated PAI-1 level during the PET was likely from the local production and release of PAI-1. It had an inverse relationship with the amount of ultrafiltration. Repeated inflammation of the peritoneum was associated with an increased production and release of PAI-1 into the peritoneum.

Adolescent↗