Aldosterone stimulates surface expression of NHE3 in renal proximal brush borders.

The mineralocorticoid aldosterone is one of the major regulators of extracellular volume and blood pressure. It acts by enhancing Na(+) reabsorption across tight epithelia such as renal collecting ducts and colon. In addition, it has been shown that aldosterone stimulates NaCl and volume reabsorption in renal proximal tubules by an unknown mechanism.

Contraluminal transport of organic cations in the proximal tubule of the rat kidney. I. Kinetics of N1-methylnicotinamide and tetraethylammonium, influence of K+, HCO3-, pH; inhibition by aliphatic primary, secondary and tertiary amines and mono- and bisquaternary compounds.

In order to study the characteristics of contraluminal organic cation transport from the blood site into proximal tubular cells the stopped-flow capillary perfusion method was applied. The disappearance of N1-[3H]methylnicotinamide (NMeN+) and [3H]tetraethylammonium (TEA+) at different concentrations and contact times was measured and the following parameters evaluated: Km,NMeN = 0.54 mmol/l, Jmax,NMeN = 0.

Contraluminal p-aminohippurate transport in the proximal tubule of the rat kidney. VIII. Transport of corticosteroids.

Using the stop-flow peritubular capillary microperfusion method contraluminal transport of corticosteroids was investigated (a) by determining the inhibitory potency (apparent Ki values) of these compounds against p-aminohippurate (PAH), dicarboxylate (succinate) and sulphate transport and (b) by measuring the transport rate of radiolabelled corticosteroids and its inhibition by probenecid. Progesterone did not inhibit contraluminal PAH influx but its 17 alpha- and 6 beta-hydroxy derivatives inhibited with an app. Ki of 0.

Contraluminal p-aminohippurate transport in the proximal tubule of the rat kidney. VII. Specificity: cyclic nucleotides, eicosanoids.

Using the stop-flow peritubular capillary microperfusion method the inhibitory potency (apparent Ki values) of cyclic nucleotides and prostanoids against contraluminal p-aminohippurate (PAH), dicarboxylate and sulphate transport was evaluated. Conversely the contraluminal transport rate of labelled cAMP, cGMP, prostaglandin E2, and prostaglandin D2 was measured and the inhibition by different substrates was tested. Cyclic AMP and its 8-bromo and dibutyryl analogues inhibited contraluminal PAH transport with an app.

Contraluminal bicarbonate transport in the proximal tubule of the rat kidney.

In order to measure the contraluminal bicarbonate flux in situ we applied the stopped flow capillary microperfusion technique and measured the influx of 14C-bicarbonate buffer into cortical tubular cells at pH 8. It was found that the influx in percent of the starting concentration is larger at 20 mmol/l bicarbonate than at 1 mmol/l, indicating a sigmoidal type influx curve. At 20 mmol/l bicarbonate the influx was inhibited by 44%, when Na+ was replaced by choline.

Contraluminal transport of small aliphatic carboxylates in the proximal tubule of the rat kidney in situ.

In order to study the characteristic of contraluminal transport of hydrophylic small fatty acids the in situ stopped flow microperfusion technique [12] has been applied. By measuring with 4 s contact time the decrease in the contraluminal concentration of the respective radiolabelled substances the concentration dependence of the influx into the cortical cells was tested. The 4 s decrease in contraluminal concentration of chloroacetate, L-lactate, D-lactate, 3-hydroxybutyrate and acetoacetate was between 26% and 31%.

Contraluminal transport of hexoses in the proximal convolution of the rat kidney in situ.

In order to study contraluminal hexose transport, concentration and time-dependent influx of 3H-2-deoxy-D-glucose from the interstitium into cortical tubular cells has been measured. The influx curves fit to a two parameter kinetics (Km 1.3 +/- 0.

Contraluminal phosphate transport in the proximal tubule of the rat kidney.

In order to study the characteristics of contraluminal phosphate transport the stopped flow microperfusion technique [13] has been applied. By measuring the time-dependent decrease of interstitial 33Pi concentration at different starting concentrations a simple diffusion kinetics with a permeability coefficient of 7.5 +/- 1.

A cytotoxin of Pseudomonas aeruginosa acts directly on the cortical thick ascending limb of Henle's loop of rabbit kidney.

The present study examines directly the effect of a cytotoxin of Pseudomonas aeruginosa on the in vitro perfused rabbit cortical thick ascending limb of the loop of Henle (cTAL). 25 cTAL segments were perfused at high rate. The open circuit transepithelial electrical PD (PDte) and the specific electrical transepithelial resistance (Rt) were recorded continuously.

Bicarbonate reabsorption in the papillary collecting duct of rats.

Using the technique of capillary perfusion and simultaneous luminal stop flow microperfusion the reabsorption of bicarbonate and glycodiazine from the papillary collecting duct was evaluated. Starting with equal H14CO3- and 3H-glycodiazine concentrations in the luminal and peritubular perfusates, the decrease in the luminal concentration at 10 and 45 s contact time was measured. In control rats with 25 mmol/l HCO3- in the perfusates the rate of HCO3- reabsorption calculated from the 10 s values was 0.

Sodium reabsorption in the papillary collecting duct of rats. Effect of adrenalectomy, low Na+ diet, acetazolamide, HCO-3-free solutions and of amiloride.

Using the shrinking droplet method and simultaneous perfusion of the peritubular capillaries the isotonic reabsorption of Ringer's solution from the papillary collecting ducts was measured. Under control conditions the volume reabsorption from the papillary collecting ducts was Jv +/- SE = 2.6 +/- 0.

Coupling between proximal tubular transport processes. Studies with ouabain, SITS and HCO3-free solutions.

The rate of active transport by the proximal renal tubule of amino acid (L-histidine), sugar (alpha-methyl-D-glycoside), H+ ions (glycodiazine), phosphate and para-aminohippurate was evaluated by measuring the zero net flux concentration difference (deltac) of these substances. In the case of calcium the electrochemical potential difference (delta + zF-CIdeltaphi/RT) was the criterion employed. The rate of isotonic Na+-absorption (JNa) was measured with the shrinking droplet method.

Effect of parathyroid hormone and cyclic adenosine 3',5'-monophosphate on isotonic fluid reabsorption: polarity of proximal tubular cells.

Isotomic fluid reabsorption (JV) of rat renal proximal tubules was examined by the shrinking droplet method in combination with simulatneous perfusion of blood capillaries. Sensitivity of JV measurement was improved by using each punctured tubule for control measurements: 1) Parathyroid hormoen (PTH) on the contraluminal cell side reduced JV in a dose-response behavior. The maximal inhibition was achieved at a PTH concentration of 10(-5) M, the half maximal inhibition at a concentration of 3 X 10(-9) M.

Effect of cyclic nucleotides on the isotonic fluid reabsorption in the proximal convoluted tubule of rat kidney.

In order to reveal the sidedness of the cyclic AMP action on renal tubules the effect of cyclic nucleotides on isotonic fluid reabsorption was examined in proximal convoluted rat kidney tubules by using advanced micropuncture techniques. Cyclic AMP inhibited isotonic fluid reabsorption preferentially when applied on the luminal cell side. This finding coincides with a predominant distribution of a membrane bound cyclic AMP dependent protein kinase in a luminal cell membrane fraction.