Search PubMed⌕ Search

Biomedical subjects

G Kottra

Publications and source records attributed to G Kottra.

27 records · Page 2Linked to original sources
PubMed1984

Rapid determination of intraepithelial resistance barriers by alternating current spectroscopy. II. Test of model circuits and quantification of results.

The impedance of Necturus gallbladder epithelium was measured with transepithelial and intracellular microelectrodes in different transport states. The data are analysed with five electrical equivalent circuits, which differ with respect to the configuration of the paracellular shunt path (lumped vs distributed model of the lateral space), and of the apical cell membrane (non-ideal capacitance or surface amplification by micro-tubular infoldings). Least square fits indicate: 1. that the lumped model cannot represent the epithelium properly, even under control conditions; 2. that the distributed model, which considers the lateral intracellular space separately as a cable-like structure, describes the data well, both under control conditions and during collapse of the lateral spaces; and 3. that the above indicated variations of the apical membrane configuration improve the fits, but have little effect on the magnitude of the calculated circuit parameters. Quantitatively the analysis of 214 measurements on 25 gallbladders under control conditions yields the following results: The resistances of the tight junctions, of the lateral intercellular space, and of the apical and basal cell membrane are Rj = 123, Rlis = 35.5, Ra approximately 3,500, and Rb = 225 (all in omega cm2), and the capacitances of the cell membranes are Ca = 4.95 and Cbl = 26.5 (mu F/cm2). In oxygen deficiency and after cessation of chamber perfusion transport decreased, the spaces collapsed, and Rlis increased to approximately 130 omega cm2. Although the accuracy of the estimated Ra values is still limited, the analysis shows that it is possible to determine Rj and Rlis separately and to follow their changes in response to experimental maneuvers.

Animals↗
PubMed1983

Intratubular and peritubular capillary hydrostatic and oncotic pressures after chronic renal sympathectomy in the anaesthetized rat.

The possible role of peritubular capillary physical forces in the diuretic-natriuretic effects of chronic renal denervation was investigated in Inactin-anaesthetized nondiuretic control (C) and unilaterally denervated (D) rats. Micropuncture techniques were combined with measurement of intratubular and peritubular capillary hydrostatic pressures and afferent and efferent arteriolar plasma oncotic pressures were determined, as well. Compared to data of C rats and of innervated kidneys, marked denervation diuresis and natriuresis were seen without changes in GFR. Both late proximal and early distal (F/P)In values were significantly lower in D kidneys with similar SNGFR. Afferent (pia) and efferent (pi e) arteriolar oncotic pressures were unchanged by denervation (C-pi a = 23.3 +/- 0.79, pi e = 29.9 +/- 0.87 mm Hg; D-pi a = 23.2 +/- 0.94, pi e = 29.8 +/- 1.04 mm Hg). Proximal intratubular hydrostatic pressure was moderately but significantly higher in D kidneys (C = 11.9 +/- 0.5, D = 13.7 +/- 0.3 mm Hg, P less than 0.01), while peritubular capillary pressures were: efferent arteriole (C = 13.9 +/- 0.5, D = 13.4 +/- 0.6 mm Hg, NS). It is concluded that the tubular effects of chronic renal sympathectomy are not dependent on changes in Starling forces of the peritubular environment.

Animals↗
PubMed1983

Functional properties of the paracellular pathway in some leaky epithelia.

We here review the functional properties of the paracellular pathway of leaky epithelia such as gallbladder and renal proximal tubule. These epithelia are characterized by leaky terminal bars between adjacent cells which allow small ions, non-electrolytes and water to leak from lumen to interstitial fluid or back. In the past 10 years a great deal of information has been obtained about the properties of the misnamed 'tight' junctions in the terminal bars, by assuming that the overall permeation pattern reflected predominantly the junctional permeation properties. Although recent trans- and intraepithelial impedance analyses indicate that this assumption is not always justified (the contribution of the lateral intercellular space to the paracellular shunt resistance is not negligible, when the spaces are collapsed) it seems that the major conclusions are correct. The properties of the terminal junctions may thus be summarized as follows. (1) Large molecules such as horseradish peroxidase are not able to pass. (2) Passage of lipophilic substances is insignificant, as these substances permeate by the cellular route. (3) Depending on the tissue, ion permeation is either governed by channels with negative fixed charges, or positive fixed charges, or both. As inferred from ion selectivity patterns the channels of different epithelia are either wide and highly hydrated or narrow and poorly hydrated, thus allowing more or less water molecules to pass besides the ions. In narrow channels single-file diffusion may occur. (4) Besides the selective channels a free solution shunt seems to be present in some epithelia. (5) When applied in millimolar concentrations 2,4,6-triaminopyrimidinium and amiloride block negatively charged junctional channels. However these substances do not simply turn leaky epithelia into tight epithelia, because they have additional effects on the cell membranes. (6) As observed in cell cultures, formation of tight junctions requires connecting particles to be present on the cell surface--which seems to be controlled by the cytoskeleton-- and requires the presence of calcium ions as ligands. (7) Cellular control over paracellular permeability may be exerted through changes of intracellular calcium concentration.

Animals↗
PubMed1982

A simple method for constructing shielded, low-capacitance glass microelectrodes.

A new simple method is presented to produce shielded low-capacitance microelectrodes. A metal-shield is vapour-deposited on the inner surface of a glass pipette which is slid over the microelectrode proper and insulated at the tip by dipping in polystyrene. The unshielded protruding tip can be as small as 10 micrometers. A special advantage is the low capacitance between electrode and shield of approximately 0.16 microF/cm shield length.

Glass↗
PubMed1982

Square wave pulse analysis of cellular and paracellular conductance pathways in Necturus gallbladder epithelium.

In search for a rapid and reliable method to identify and quantitatively determine cell membrane resistances and paracellular shunt resistances in epithelia we have developed appropriate techniques to measure transepithelial and intracellular potential transients in response to transepithelially applied square wave constant current pulses. Model considerations indicate that in a unilayered, homogeneous epithelium with open lateral spaces the transient potential response across each cell membrane should obey a single exponential function in case the tight junction resistance is high, as in a tight epithelium, whereas in a leaky epithelium it should consist of a superposition of two exponentials with equal sign at the membrane with the higher intrinsic time constant and of two exponentials of different sign (overshoot with recline) at the membrane with the lower intrinsic time constant. The latter predictions were experimentally verified in a study on Necturus gallbladder epithelium and equivalent circuit parameters for the cell membrane resistances and capacitances as well as for the resistance of the shunt path were calculated from the data by curve fitting procedures. The resistances of the apical and basal cell membrane and of the shunt path averaged 1220, 201 and 91 omega cm2 respectively while the apical and basal cell membrane capacitances were 8.0 and 26.3 micro F/cm2 respectively. The fact that the resistance values are 4-15 times lower than estimates derived previously from 2D-cable analysis relates to a better preservation of the transport function under the present incubation conditions as verified by a new series of cable analysis data. The capacitances agree well with estimates of the surface amplification of the cell membranes from electronmicrographs, thus confirming the validity of the interpretation of the observed voltage transients.

Animals↗
PubMed1981

Renorenal vasomotor reflex.

The acetylcholine induced contralateral renorenal vasomotor reflex has been re-examined. In dogs under pentobarbital anaesthesia blood flow of the contralateral kidney as measured by electromagnetic flow probe did not change after an infusion or bolus injection of Ach. Basal sympathetic nervous activity of the contralateral kidney increased only slightly and these changes correlated with the decrease of arterial blood pressure. In conclusion, the renorenal vasomotor reflex could not be evoked under the present experimental conditions.

Acetylcholine↗
PubMed1981

Effect of renal denervation on free flow proximal tubular potential difference in the rat.

Proximal transtubular potential difference (PD) was measured using the semi-microelectrode technique in control (C, n = 10) and unilaterally denervated (D, n = 10) rats. Acute renal sympathectomy resulted in a twofold and fourfold increase in diuresis and sodium excretion, respectively, with no change in GFR. PD (mean +/- S.E.M.) in the earliest accessible proximal convolutions (EPT) of group C was +/- 0.27 +/- 0.08 mV (n = 16), while in group D it was -0.16 +/- 0.07 mV (n = 18) (p less than 0.01). PD in mid (MPT) and late (LPT) proximal segments was unchanged by denervation (MPT: C = 0.94 +/- 0.05, n = 21; D = 0.98 +/- 0.04, n = ns. LPT: C = 1.04 +/- 0.11, n = 17; D = 0.95 +/- 0.06, n = 18 NS.). The shift to the negative of PD in EPT caused by denervation lends support to our earlier suggestion that active transport of solutes and organic substances is depressed by sympathectomy in the proximal tubule. The unaltered PD in MPT and LPT seems to indicate that passive forces promoting reabsorption in this part of the nephron are probably preserved.

Animals↗
PubMed1979

Effect of a "minimal natriuretic and diuretic" dose of prostaglandin E1 (PGE1) on the intratubular and peritubular pressures in anaesthetized rats.

A "minimal natriuretic and diuretic" dose (3.4--4.2 ng/min/kg) of prostaglandin E1 (PGE1) as previously estimated was infused into the aorta in anaesthetized rats. During the PGE1 infusion parameters for renal haemodynamics, Na+ and water excretion, intra- and peritubular pressures were studied ("electronic servo nulling device"). During the solvent period parameters for the infused left kidney did not differ from those on the control side. Diuresis and Na+ excretion were increased significantly due to PGE1 infusion in both series of investigations. Cortical blood flow (radio isotope labelled microsphere technique) and glomerular filtration (inulin clearance) did not change significantly. Oncotic pressure in the afferent arteriole was not affected by PGE1, whereas it was reduced significantly in the efferent arteriole (control, 22.9 +/- 1.7; PGE1, 19.2 +/- 0.9 mmHg). Transit times to the early and late distal tubules were not affected by PGE1. There were no changes in the hydrostatic pressure in the proximal tubule and efferent arteriole, whereas the peritubular capillary hydrostatic pressure was significantly increased (control, 9.6 +/- 0.3; PGE1, 11.2 +/- 0.2 mmHg). The present results indicate that PGE1 is capable of enhancing Na+ and water excretion without affecting RBF and GFR, and peritubular physical factors might play an auxiliary role in this effect.

Animals↗