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Biomedical subjects

R Greger

Publications and source records attributed to R Greger.

At least 91 records · Page 5Linked to original sources
PubMed1984

Potassium activity in cells of isolated perfused cortical thick ascending limbs of rabbit kidney.

The Na+2Cl-K+ cotransporter in the apical membrane of the cortical thick ascending limb of the Henle's loop (cTAL) of rabbit nephron utilizes the electrochemical gradient for Na+ to transport K+ and Cl- against an unfavorable electrochemical gradient from lumen to cell interior. In the present study attempts are made to measure intracellular K+ activity (a cell K+) under control conditions and after inhibition of the cotransport system by furosemide (50 X 10(-6) mol X l-1). 70 cTAL segments of 55 rabbits were perfused in vitro. Conventional Ling-Gerard and K+-selective microelectrodes were used to measure the PD across the basolateral membrane (PDbl) as well as the PD sensed by the single barrelled K+-selective electrode (PDK+). PDbl was -64 +/- 1 (n = 65) mV and PDK+ + 15 +/- 1 (n = 32) mV under control conditions. The positive PDK+ value, significantly different from zero, indicates that a cell K+ is higher than predicted for passive distribution. The estimate for a cell K+ obtained from PDbl and PDK+ was 113 +/- 8 mmol X l-1. Furosemide lead to the previously reported hyperpolarization of PDbl by 17 +/- 4 (n = 13) mV and to a reduction of PDK+ from 15 +/- 1 to 5 +/- 1 (n = 20) mV. The a cell K+, obtained from this set of data, was 117 +/- 9 mmol X l-1, and was not different from the control value. The present data indicate that a cell K+ is significantly above Nernst equilibrium under control conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Mechanism of NaCl secretion in rectal gland tubules of spiny dogfish (Squalus acanthias). II. Effects of inhibitors.

Rectal gland tubule (RGT) segments of the spiny dogfish (Squalus acanthias) were perfused in vitro. The effects of inhibitors of known mode of action on transepithelial PD (PDte resistance (Rte), the PD across the basolateral membrane (PDbl), the fractional resistance of this membrane (FRbl), and intracellular activities of NA+, Cl-, K+ (apha cell) were examined. Furosemide (5 x 10(-4) mol x 1(-1)) reduced PDte from -12 +/- 0.7 to -2.3 +/- 0.2 mV (n = 63), hyperpolarized PDbl from -71 +/- 1.3 to -79 +/- 0.9 mV (n = 59), FRbl decreased from 0.2 +/- 0.03 to 0.13 +/- 0.01 (n = 21), alpha cell cl- fell from 38 +/- 4 to 11 +/- 2 mmol x 1(-1) (n = 21), alpha cell Na+ fell from 37 +/- 4 to 17 +/- 2 mmol x 1(-1) (n = 12) and alpha cell K+ was constant [113 +/- 14 vs. 117 +/- 15 mmol x 1(-1) (n = 6)]. Furosemide exerted its effects within some 20-40s. Its action was completely reversible. Analysis of the time courses revealed that the furosemide induced initial fall in alpha cell cl- was approximately twice as rapid when compared to that of alpha cell Na+. Ba2+ 0.5 mmol x 1(-1) (bath) reduced PDte from -7.1 +/- 1.2 to -4.1 +/- 0.6 mV (n = 24), increased Rte from 18 +/- 2 to 22 +/- 2.5, omega cm2 (n = 14). PDbl depolarized from -75 +/- 2 to -48 +/- 2 mV (n = 42), FRbl increased from 0.2 +/- 0.02 to 0.34 +/- 0.04 (n = 14) and alpha cell K+ increased from 143 +/-28 to 188 +/- mmol x 1(-1) (n = 4). Ouabain (50 x 10(-6) mol x 1(-1), bath) reduced PDte from -12 +/-2 to -3 +/- 0.5 mV (n = 9), Rte increased from 18 +/- 3 to 21 +/- 3 omega cm2 (n = 5). PDbl depolarized from -67 +/- 4 to -26 + 3 mV (n = 14), FRbl increased from 0.23 +/- 0.04 to 0.45 +/- 0.05 (n = 6), alpha cell K+ fell only slightly from 135 +/- 15 to 112 +/- 30 mmol x 1(-1) (n = 4), but alpha cell cl- increased from 35 +/- 12 to 111 +/- 37 mmol x 1(-1) (n = 3). These effects of ouabain were slow when compared to those exerted by furosemide or Ba2+. The ouabain effects on PDte and PDbl were completely prevented if furosemide was applied first.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1984

Mechanism of NaCl secretion in rectal gland tubules of spiny dogfish (Squalus acanthias). III. Effects of stimulation of secretion by cyclic AMP.

Segments of rectal gland tubules (RGT) the spiny dogfish (Squalus acanthias) were perfused in vitro to study the cellular mechanism by which NaCl secretion is stimulated. Transepithelial PD (PDte), transepithelial resistance (Rte), the PD across the basolateral membrane (PDbl), the fractional resistance of the lumen membrane (FR1), and the cellular activities for Cl-, Na+, and K+ (alpha cell x) were measured. In series 1 the effects of stimulation (S) (dbcAMP 10(-4, adenosine 10(-4), and forskolin 10(-6) mol x 1(-1) on these parameters were recorded and compared to nonstimulated state (NS). PDte increased from -1.9 +/- 0.2 mV to -11.0 +/- 0.9 mV (n = 51). PDbl depolarized from -86 +/- 1 to -74 +/- 1.4 mV (n =52), Rte fell from 29 +/- 2.8 to 21 +/- 2 omega cm2 (n = 23), and FR1 fell from 0.96 +/- 0.005 to 0.79 +/- 0.04 (n = 9). alpha cell K+ was constant (123 +/- 13 versus 128 +/- 17 mmol x 1(-1) (n = 6), but alpha cell cl- fell significantly from 48 +/- 4 to 41 +/- 3 mmol x 1(-1) (n = 7). alpha cell Na+ increased from 11 +/- 2.1 to 29.5 +/- 6.6 mmol x 1(-1) (n = 4). In series 2 the conductivity properties were examined by rapid K+, and Cl- concentration steps on the basolateral and luminal cell side respectively in NS and S states. In NS-segments reduction of bath K+ led to a hyperpolarization of PDbl with a mean slope of 28 +/- 1.3 mV/decade (n = 9) (as compared to 19 mV/decade for S-state).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Single channel recordings from basolateral and apical membranes of renal proximal tubules.

A new method is described, which enables the recording of single ionic channels from the basolateral as well as the luminal membrane of renal proximal tubules with the patch-clamp technique. Segments of late proximal tubules of rabbit kidney are cannulated and perfused from one end. The other end is open and freely accessible to a patch pipette. The patch electrode can be moved against lateral cell membranes or can be inserted through the open end into the lumen and brought to contact with the brush-border membrane. Both, in the basolateral as well as in the luminal membrane, giga seals can be achieved. In both membranes, K+ selective channels could be identified.

Animals↗
PubMed1984

Substrate utilization in the isolated perfused cortical thick ascending limb of rabbit nephron.

Isolated segments of cortical thick ascending limbs (cTAL) of rabbit kidney were perfused in vitro and the equivalent short circuit current (Isc) was measured. In a first series all substrates were removed on either side. Isc fell rapidly to 50 +/- 12% after 3 min and to 27 +/- 6% (n = 5) after 10 min. This indicates that in cTAL segments Isc is strictly dependent on the presence of substrates. In series two it was tested what substrates can be utilized by the cTAL segment, and from which epithelial side [bath (b) or lumen (1)] the substrates are taken up. From the 1-side only butyrate (10 mmol X 1(-1) sustained the Isc at 95 +/- 2% (n = 7). All other tested substrates (10 mmol X 1(-1): pyruvate, acetate, beta-OH-butyrate, D-glucose, and L-lactate lead to a marked decline in Isc. From the b-side several substrates (5--10 mmol X 1(-1) sustained the Isc: D-glucose, D-mannose, butyrate, beta-OH-butyrate, acetoacetate, L-lactate, acetate and pyruvate. Other compounds (1--10 mmol X 1(-1): citrate, alpha-ketoglutarate, succinate, glutamate, glutamine, propionate, caprylate and oleate did not sustain Isc. In the third series the mechanism of substrate utilization from the basolateral cell side was studied. It was shown that the Isc is a saturable function of the D-glucose, L-lactate, acetate, pyruvate or beta-OH-butyrate concentration with apparent Km's between 0.05--1.0 mmol X 1(-1). Several known inhibitors of sugar and of anion transport were tested at the bath side: phlorrhizin was without effect. Phloretin (500 mumol X 1(-1) inhibited Isc by 96%, yet its effect was not dependent on the presence of substrates on the b-side since inhibition occurred also if the b-perfusate contained no substrate and Isc was driven by luminal butyrate. Also SITS (5 mmol X 1(-1) exerted only a small inhibitory effect which was not specific since it was also observed with luminal butyrate. alpha-Cyano-m-OH-cinnamate (10 mmol X 1(-1) inhibited the Isc specifically when L-lactate was the bath substrate. Probenecid (1 mmol X 1(-1) had a similar yet less marked inhibitory effect. The D-glucose uptake from the b-side was specifically inhibited by cytochalasin B at 5 X 10(-6) mol X 1(-1). We conclude that the cTAL segment of the rabbit utilizes D-glucose and/or small anions such as pyruvate or L-lactate or acetate to energize salt reabsorption.(ABSTRACT TRUNCATED AT 400 WORDS)

Absorption↗
PubMed1984

Mechanism of NaCl secretion in the rectal gland of spiny dogfish (Squalus acanthias). I. Experiments in isolated in vitro perfused rectal gland tubules.

Rectal gland tubules (RGT) of spiny dogfish were dissected and perfused in vitro. Transepithelial PD (PDte), resistance (Rte), the PD across the basolateral membrane (PDbl) and intracellular chloride and potassium activities (a cell Cl-, a cell K+) were measured. In a first series, 67 RGT segments were perfused with symmetric shark "Ringers" solution. The bath perfusate contained in addition db-cAMP 10(-4), forskolin 10(-6), and adenosine 10(-4) mol X 1(-1). PDte was -11 +/- 1 (n = 67) mV lumen negative, Rte 27 +/- 2 (n = 47) omega cm2, PDbl -75 +/- 0.4 (n = 260) mV. a cell K+ and a cell Cl- were 109 +/- 22 (n = 4) and 38 +/- 4 (n = 36) mmol X 1(-1) respectively. These data indicate that Cl-secretion across the RGT must be an uphill transport process, whereas secretion of Na+ could be driven by the lumen negative PDte. Intracellular K+ is 14 mV above equilibrium with respect to the basolateral membrane PD and Cl- is 23 mV above equilibrium across the apical membrane. In series 2, the conductivity properties of the apical and basolateral membrane as well as that of the paracellular pathway were examined in concentration step experiments. Decrease of the basolateral K+ concentration led to a rapid hyperpolarization of PDbl with a mean slope of 19 mV per decade of K+ concentration change. Addition of 0.5 mmol X 1(-1) Ba2+ to the bath solution lead to a marked depolarization and abolished the response to K+ concentration steps. In the lumen a Cl- concentration downward step led to a depolarization of the lumen membrane; resulting in a mean slope of 18 mV per decade of Cl- concentration change. When dilution potentials were generated across the epithelium, the polarity indicated that the paracellular pathway is cation selective. In series 3 the equivalent short circuit current (Isc = PDte/Rte) was determined as a function of symmetrical changes in Na+ concentration, with Cl- held at 276 mmol X 1(-1), and as a function of symmetrical changes in Cl- concentration, with Na+ held at 278 mmol X 1(-1). Isc was a saturable function of Na+ concentration (Hill coefficient 0.9 +/- 0.1, K1/2 4.4 mmol X 1(-1), n = 7) and also a saturable function of Cl- concentration (Hill coefficient 2.0 +/- 0.1, K1/2 75 mmol X 1(-1), n = 11).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Cellular mechanism of the action of loop diuretics on the thick ascending limb of Henle's loop.

During the passed few years the cellular mechanisms responsible for the NaCl reabsorption in the thick ascending limb of the Henle loop of mammalian nephron and of the early distal tubule of amphibian kidney have been extensively studied. From these studies a new type of secondarily active transport mechanism, i.e. the Na+--2Cl- --K+ symport has emerged. Meanwhile it has been recognized that this system is also present in many other epithelia. All these epithelia share in common that they are sensitive to the so called loop diuretics. The present article summarizes our current knowledge of how the loop diuretics, by reversible interaction with the above cotransport system, inhibit the NaCl reabsorption in the thick ascending limb of Henle's loop. It is shown that these drugs transfer the thick ascending limb cell to a state in which not only transepithelial NaCl reabsorption ceases but in which also very little energy is consumed since then K+ and Cl- "relax" to passive distribution across both cell membranes and Na+ entry into the cell is blocked.

Absorption↗
PubMed1983

Chloride activity in cells of isolated perfused cortical thick ascending limbs of rabbit kidney.

Rabbit cortical thick ascending limb segments were perfused in vitro, and intracellular Cl- activity was estimated in three types of experiments using conventional and chloride selective microelectrodes. In series 1 Ringer like solutions were present on the two epithelial sides. In series 2 limen Cl- was replaced by gluconate, and in series 3 furosemide, 10-20 . 10(-6) mol . 1-1, was added to the lumen perfusate. It was found that under control conditions intracellular Cl- activity, as estimated from the difference of the reading of the conventional (n = 53) and ion selective electrodes (n = 118) was 26 +/- 1 mmol . 1-1. Thi value is approximately three times higher than expected for passive distribution of Cl-. After removal of lumen Cl- (series 2) intracellular Cl- activity fell to 9 mmol . 1(-1) which is only some 4 mmol . 1(-1) above passive distribution. We argue that these 4 mmol . 1(-1) reflect mainly the interference with the Cl- electrode by other anions, such as phosphate. The above estimates for intracellular Cl- activity, have to be diminished by these 4 mmol . 1(-1), and, thus, are close to 22 mmol . 1(-1). In series 3 a rapid and reversible fall in intracellular Cl- from 23 to 7 mmol . 1(-1) was observed. We conclude that the Cl- activity in cTAL cells is clearly above equilibrium under control conditions and that it falls rapidly to values close to equilibrium when Cl- reabsorption is blocked by either removing lumen Cl- or by blocking the Cl- entry via the Na+-2 Cl--K+-carrier with furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Influence of calcium and ionophore 23187 on tubular phosphate reabsorption.

In previous studies it has been demonstrated that a decline of plasma calcium concentration accounts for the decrease of phosphate reabsorption in thyroparathyroidectomized (TPTX) rats undergoing phosphate loading. Microinfusion studies were performed in TPTX rats in order to discriminate between a systemic effect of calcium an a direct renal effect. Thyroparathyroidectomized animals were infused with a phosphate solution continuously. When plasma calcium concentration fell below 1.30 mmol/l, proximal convoluted tubules were microinfused with a phosphate tracer solution for 42 min. After 18 min a calcium chloride-containing solution was applied superficially (superfused) to the area of the microinfused tubule. This elevation of peritubular calcium concentration led to an immediate increase of phosphate reabsorption up to 12% of the microinfused phosphate load within 24 min. In another series of experiments, the calcium specific ionophore A23187--a substance which is known to increase intracellular calcium--was superfused on the microinfused tubule. This resulted again in an increase of fractional phosphate reabsorption of about 15% after 24 min. In contrast, when calcium chloride-free as well as ionophore-free solutions were superfused fractional phosphate reabsorption decreased (7%). From these data we conclude that 1. calcium has a direct renal effect on phosphate reabsorption in the absence of parathyroid hormone and 2. intracellular calcium appears to be a major parameter in the regulation of renal phosphate transport under these conditions.

Animals↗
PubMed1979

Renal handling of urate and oxalate: possible implications for urolithiasis.

Both urate and oxalate are organic acids of considerable clinical interest, owing to their limited solubility. Calcium oxalate is the most frequent constituent of renal calculi and occasionally precipitates in body fluids. Urate precipitations are common in the kidney and in various other tissues. In this paper, a short outline of the present knowledge of renal handling of these substances will be followed by some conclusions as to the possible relevance of this knowledge for the understanding of urolithiasis and intrarenal precipitation. Direct (micropuncture) data are available for urate in the rat (1, 6, 7, 10, 21, 23, 28, 36, 42), rabbit (35), dog (34) and cebus monkey (33) and in the rat only for oxalate (11, 15, 20).

Alkalies↗
PubMed1978

Effect of benzolamide on luminal pH in proximal convoluted tubules of the rat kidney.

Luminal pH in early and late proximal tubules was recorded continuously with antimony microelectrodes before and during carbonic anhydrase inhibition. Following i.v. application of benzolamide (25 mumol/kg BW), luminal pH decreased almost immediately in early proximal tubules (deltapH--0.42 +/- 0.06SEM), but increased in late proximal tubules (deltapH +0.27 +/- 0.06). Urinary pH increased (deltapH + 1.6 +/- 0.16) after a delay of some 30 s. Similar results, i.e. decrease of pH in early and increase of pH in late proximal tubules, were obtained, when benzolamide containing solutions were microinfused into early proximal tubules or superfused on the nephron surface. In contrast, luminal pH decreased in late proximal tubules, when benzolamide was microinfused into the same nephron segment. The decrease of luminal pH indicates inhibition of luminally active carbonic anhydrase, leading to delayed buffering of secreted hydrogen ions. The increase of luminal pH in late proximal tubules may be attributed to several factors including increased delivery of bicarbonate, impaired bicarbonate exit at the antiluminal membrane and decreased hydrogen ion formation in the tubular cell due to inhibition of cellular carbonic anhydrase.

Animals↗
PubMed1978

Distal site of calcium reabsorption in the rat nephron.

The site of outflux of 45Ca along the nephron were investigated using microinfusion technique in acutely thyroparathyroidectomized (TPTX), intact and TPTX Wistar rats substituted with parathyroid hormone (PTH). In all three groups 45Ca outflux occurred along the proximal tubule, the loop of Henle and along the distal tubule. After microinfusion into late distal tubules 45Ca recovery in ipsilateral urine was essentially complete for the TPTX group but was only 83 and 65% for the intact and the PTH substituted animals. Increases in microinfusion flow rate from 2--20 nl/min into early and middle distal tubules resulted in increased urinary recovery of 45Ca for all three groups. Similarily, increases in microinfusate Ca concentration from 0.2--2.0 and 5.0 mmol/l resulted in increased fractional urinary recovery of 45Ca both in the presence and absence of PTH. When 45Ca and 3H insulin containing solutions were continuously microinfused into early distal tubules for one hour periods an anticalciuric effect of PTH could be demonstrated. It is concluded that Ca, in addition to its outflux in the proximal tubule and in the loop of Henle, is reabsorbed in the distal tubule accessible to micropuncture. PTH acts anticalciuric at this latter site.

Animals↗
PubMed1978

[Uptake of 2-C14 urate by erythrocytes in hyperuricemia and in gout (author's transl)].

The uptake of 2-C14 urate by erythrocytes was measured in 19 patients with primary hyperuricemia, 6 patients with secondary hyperuricemia, 17 patients with primary gout and 30 controls. The uptake of urate in patients with primary gout was significantly lower than in the controls. In contrast no such difference could be observed in patients with primary and secondary hyperuricemia. The uptake of labeled urate by erythrocytes from gouty patients is especially diminished in the early phase of the uptake kinetics. The possible relevance of this finding for the pathogenesis of urate precipitation in gout is discussed. Further, we consider the application of the tracer urate uptake by erythrocytes as an aid in the early diagnosis of gout.

Erythrocytes↗