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F Morel

Publications and source records attributed to F Morel.

At least 181 records · Page 10Linked to original sources
PubMed1986

Effects of external potassium concentrations on the cell sodium and potassium contents of isolated rat kidney tubules.

The effects of 20 mumol/l amiloride, 10 mumol/l furosemide and 1 mmol/l ouabain on cell Na and K concentrations were investigated by flame microphotometry in isolated rat medullary collecting tubules and medullary thick ascending limbs (MCT and MAL) as a function of the external potassium concentration [Ke]. The results are expressed as Na and K concentrations per liter cell volume ([Nac] and [Kc], mmol/l) and relative sodium content, [Nac]/([Nac] + [Kc]). From the experimental curves, [Ke]1/2 is defined as the [Ke] value corresponding to half maximal exchange of K against Na in cells. When [Ke] was 5 mmol/l, the relative Na content was less than 15% in control and amiloride-treated MCT as well as in control and furosemide-treated MAL, and about 24% in ouabain-treated MCT and MAL. In MCT, relative cell Na content increased up to 90% or more when [Ke] was reduced from 2.5 to 0.25 mmol/l. [Ke]1/2 was 0.55, 0.45 and 1.25 mmol/l for control, amiloride-treated and ouabain-treated MCT respectively. In MAL, similar increases in relative Na content were observed when [Ke] was reduced from 0.5 to 0.05 mmol/l. [Ke]1/2 was 0.25, 0.10 and 1.75 mmol/l for control, furosemide-treated and ouabain-treated MAL respectively. When [Ke] was reduced from 5 to 1 mmol/l, [Nac] dropped from 16.4 to 8.4 mmol/l (P less than 0.01) in control MAL. When [Ke] was 5 mmol/l, [Nac] was lower in furosemide-treated MAL (7.8 mmol/l) than control MAL (P less than 0.01). At 1 mmol/l [Ke], [Nac] was similar in both groups. These results are discussed in terms of the balance between the active and passive components of Na and K fluxes across apical and basolateral cell membranes. They indicate that a K-dependent passive Na entry process exists in the membranes of MAL cells but not of MCT cells. This process was proportionally more inhibited than the active Na pump when [Ke] was reduced from 5 to 1 mmol/l. In addition, it was found sensitive to furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Coupling of metabolic CO2 production to ion transport in isolated rat thick ascending limbs and collecting tubules.

Metabolic CO2 production from appropriate [U-14C]-labelled substrates (either L-lactate or D-glucose) was measured in single pieces of tubule as previously described (Le Bouffant et al. 1984). Changing the incubate osmotic pressure by mannitol addition resulted in an increase in oxidative metabolism which was more marked in outer-medullary segment MAL and MCT) than in cortical segments (CAL and CCT). Availability of metabolic substrate was not rate limiting under these conditions because FCCP addition (1 mumol X l-1) produced a marked rise in CO2 production in these structures. Ouabain (1 mmol X l-1) decreased by more than 50% the CO2 production by CAL, MAL, CCT and MCT samples, indicating that the larger part of oxidative metabolism was coupled to active Na transport. Furosemide addition (10(-5) mol X l-1) to CAL and MAL samples, or amiloride addition (10(-4) mol X l-1) to CCT and MCT samples reduced the rate of CO2 production to an extent almost similar to that obtained with ouabain, an observation suggesting that apical entry of Na+ was present in these non-perfused tubules. Finally, the effects of changing the concentration of either K+ or Cl- was tested in CAL samples. K+ suppression greatly depressed the rate of CO2 production. Replacement of chloride with sulfate also decreased this rate to an extent similar to that observed with furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Transport of alkali cations through thin lipid membranes by (222)C10-cryptand, an ionizable mobile carrier.

The kinetics of K+ and Na+ transport across the membrane of large unilamellar vesicles (L.U.V.) were compared at two pH's, with two carriers: (222)C10-cryptand (diaza-1,10-decyl-5-hexaoxa-4,7,13,16,21,24-bicyclo[8.8.8.]+ ++hexacosane) and valinomcyin, i.e. an ionizable macrobicyclic amino polyether and a neutral macrocyclic antibiotic. The rate of cation transport by (222)C10 saturated as cation and carrier concentrations rose. The apparent affinity of (222)C10 for K+ was higher and less pH dependent than that for Na+ but resembled the affinity of valinomycin for K+. The efficiency of (222)C10 transport of K+ decreased as the pH fell and the carrier concentration rose, and was about ten times lower than that of valinomycin. Noncompetitive K+/Na+ transport selectivity of (222)C10 decreased as pH, and cation and carrier concentrations rose, and was lower than that of valinomycin. Transport of alkali cations by (222)C10 and valinomycin was noncooperative. Reaction orders in cation n(S) and carrier m(M) varied with the type of cation and carrier and were almost independent of pH; n(S) and m(M) were not respectively dependent on carrier or cation concentrations. The apparent estimated constants for cation translocation by (222)C10 were higher in the presence of Na+ than of K+ due to higher carrier saturation by K+, and decreased as pH and carrier concentration increased. Equilibrium potential was independent of the nature of carrier and transported cation. Results are discussed in terms of the structural, physiocochemical and electrical characteristics of carriers and complexes.

Bridged Bicyclo Compounds↗
PubMed1986

Sites of prostaglandin E2 (PGE2) synthesis along the rabbit nephron.

The purpose of this study was to establish whether the nephron segments recognized as PGE2 target sites in the rabbit, i.e. the proximal tubule, the thick ascending limb and the collecting tubule, are also sites of PGE2 production. We therefore developed a microimmunoassay sensitive enough to allow the measurement of PGE2 on microdissected tubular segments about 1 mm in length. Under the conditions used (30 min incubation at 20 degrees C), a basal rate of PGE2 production was measured in the cortical (CCT) and medullary portions of the collecting tubule, as could be expected. In the presence of 10(-4) M sodium arachidonate, it was shown that: (1) The thin descending limb (TDL) is also an active site of PGE2 formation. When expressed per mm tubule length the amounts formed were lower in TDL than in CCT (14.1 +/- 2.7 SE pg/mm, n = 5, vs. 93.5 +/- 10.7, n = 8). They were quite comparable, however, when expressed per microgram total proteins (0.70 ng in TDL vs 0.6 in CCT). (2) A slight PGE2 production was noted in the connecting tubule but it was likely due to contamination by adjacent CCT cells. (3) In the other nephron segments, only negligible amounts of PGE2 were formed, which are probably of no physiological significance.

Animals↗
PubMed1986

Effects of castration on the epididymis of a non-mammalian vertebrate: evolution of morphology, protein synthesis, and of specific mRNA levels.

The lizard epididymis is an androgen-dependent organ undergoing large variations in its structure and in protein synthesis ability during its annual cycle. It produces a major androgen-dependent protein, the L protein. This work reports the effects of castration performed at 3 prominent points of the sexual cycle: stage 1 (epithelium reorganization) stage 3 (onset of secretory activity) stage 6 (full secretory activity). Evolution of various parameters (organ weight, histology, amount of soluble proteins, rate of soluble protein synthesis and of specific protein synthesis: L protein, and mRNA levels) was considered over a period ranging from 7 days to 15, 30 and 60 days. Deprivation of the testis was followed by an organ involution which was more or less accentuated or more or less rapid according to the stage of the operation but some peculiarities need to be emphasized. At first, the evolution of the organ was not stopped but it proceeded: at stage 1, there was cell division and a correlated increase in total protein synthesis (without L protein synthesis), at stage 3 total protein synthesis and L protein mRNA levels increased (synthesis of L protein proceeded up to 30 to 60 days), at stage 6 the involution was accelerated. These effects concerning stage 1 and particularly stage 3 appeared as a kind of a paradoxical induction. Secondly, the epithelium underwent phases of destruction and regeneration which were obviously not controlled by the testis.

Animals↗
PubMed1986

In vitro stimulation of Na-K-ATPase in rat thick ascending limb by dexamethasone.

Dexamethasone has been reported to stimulate Na-K-ATPase activity in the medullary thick ascending limb of adrenalectomized animals within a few hours. The present study was aimed at characterizing the mechanism of this action by investigating the stimulatory effect of the hormone in vitro. Dexamethasone (10(-8) M) added in vitro to segments of the medullary thick ascending limb of Henle's loop, which were microdissected from adrenalectomized rats, restored in a dose-dependent manner the depressed Na-K-ATPase activity within one h of incubation. This stimulation of Na-K-ATPase was inhibited by cycloheximide and actinomycin D. Dexamethasone also stimulated the component of oxidative metabolism coupled to sodium transport. These results, which confirm previous in vivo observations, demonstrate that dexamethasone-induced stimulation of Na-K-ATPase is a direct tubular action of the hormone mediated by protein synthesis. They suggest that this short-term effect of dexamethasone corresponds to the stimulation of sodium reabsorption by the dilution segment.

Adrenalectomy↗
PubMed1986

[In vitro translation of RNA from lizard epididymis and identification of poly A RNA coding for a major androgen-dependent protein].

During the reproductive period (spring) the lizard epididymis secretes a soluble protein of an apparent molecular weight (MW) of 19,000, the protein L. This androgen dependent protein disappears during post-nuptial atrophy of the epididymis (summer). At two time intervals (spring and summer) total RNA were extracted and poly (A) RNA were prepared. The RNA were translated in a cell-free system (rabbit reticulocyte lysate) in the presence of 35S methionine. Labelled translation products were analyzed by polyacrylamide gel electrophoresis under denaturing conditions. Electrophoresis were preceded or not by immunoprecipitation with an antiserum raised against protein L. RNA extracted during spring coded for several unique bands including five immunoprecipitated proteins with close-related MW (21,000 to 25,000). When RNA were translated in the presence of dog microsomes, the five previously detected protein bands disappear although a 19,000 MW immunoprecipitated protein was clearly demonstrated. These proteins were not detected when RNA extracted in summer were used. The protein L appears to be synthesized as preprotein(s). Its (unique or several?) messenger is of poly A type; it is present in spring and absent or undetectable in these experimental conditions in summer.

Androgens↗
PubMed1985

The respiratory burst of bovine neutrophils. Role of a b type cytochrome and coenzyme specificity.

A new method of preparation of bovine polymorphonuclear leukocytes (PMN) is described. The subcellular distribution of cytochrome b in resting and activated bovine PMN was compared to that of the O2-.-generating oxidase (assessed as NADPH cytochrome c reductase inhibited by superoxide dismutase). In resting PMN and in PMN activated by phorbol myristate acetate (PMA), cytochrome b was located into two membrane fractions, one of which was enriched in plasma membrane and cosedimented with alkaline phosphatase, while the other consisted of a denser material cosedimenting with markers of the specific and azurophil granules, i.e. the vitamin-B12-binding protein and myeloperoxidase respectively. During activation of PMN by PMA, 15-20% cytochrome b migrated from dense granules to the plasma membrane. The distribution of the O2-. generating oxidase and cytochrome b in subcellular particles was studied during the course of phagocytosis of PMA-coated latex beads by bovine PMN. At the onset of the respiratory burst, the phagocytic vacuoles arising from internalization of the plasma membrane were enriched in oxidase and alkaline phosphatase, but their specific content of cytochrome b was limited; in contrast, cytochrome b was predominant in denser membrane fractions cosedimenting with myeloperoxidase and the vitamin-B12-binding protein. After a few minutes of phagocytosis, a fraction of light vacuoles, slightly denser than the phagocytic vacuoles, became enriched in O2-.-generating oxidase, cytochrome b, the vitamin-B12-binding protein and myeloperoxidase. These vacuoles probably arose from the fusion of the phagocytic vacuoles with dense granules. In bovine PMN supplemented with glucose and maintained in anaerobiosis, activation by PMA induced slow reduction of cytochrome b (60-70% in 15 min at 37 degrees C). Similar results were obtained with cytoplasts after activation by PMA (30% reduction in 3 min at 37 degrees C). Cytochrome b in a particulate fraction obtained by centrifugation at 100 000 X g of an homogenate of PMA-activated PMN, was slowly reduced upon addition of NADPH under anaerobiosis (less 20% in 20 min at 37 degrees C). No reduction occurred in the 100 000 X g fraction prepared from non-activated PMN. The Soret band of cytochrome b reduced by dithionite was displaced by CO only by 1-2 nm. At subsaturating concentrations, CO had no effect on the rate of O2 uptake by activated bovine PMN.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Influence of chronic ADH treatment on adenylate cyclase and ATPase activity in distal nephron segments of diabetes insipidus Brattleboro rats.

The medullary thick ascending limb (MAL), but not the medullary collecting tubule (MCT), has been shown to have an impaired adenylate cyclase (AC) responsiveness to ADH and a selective hypoplasia in Brattleboro diabetes insipidus (DI) rats. Since chronic ADH administration has been found to increase epithelium volume and basolateral membrane surface area in MAL but not in MCT, we investigated whether chronic ADH infusion would affect the hormone-sensitive AC and the Na-K-ATPase activity--two markers of the basolateral membrane--in single micro-dissected portions of thick ascending limb and collecting tubule in DI rats. Results indicate that 1. in MAL of ADH-treated rats, AC responses to in vitro AVP and glucagon and Na-K-ATPase activity increased to the same extent as did epithelium volume (60-80%); 2. changes in the other segments were independent of any morphological alteration. In the cortical thick ascending limb, AVP and glucagon-sensitive AC decreased by 30-40% whereas Na-K-ATPase activity did not change. In the collecting tubule, AC response to in vitro AVP was not altered by ADH-treatment but glucagon-sensitive AC dropped by 50% and Na-K-ATPase activity doubled, independently of any variation in plasma aldosterone and glucagon levels. These results show that, in the MAL, the ADH-induced variations in enzyme activity are a reflection of the enlargement of the basolateral membrane surface area. Further studies are needed to clarify the origin of enzymatic alterations in the other segments.

Adenosine Triphosphatases↗
PubMed1985

Glucagon receptors along the nephron: [125I]glucagon binding in rat tubules.

Binding of [125I]glucagon was measured in microdissected pieces of tubules from the rat nephron. Specific glucagon binding sites were found only in nephron segments containing a glucagon-sensitive adenylate cyclase activity. At 7.5 nM labelled hormone, higher levels of specific binding (16-27 X 10(-18) mol mm-1) were found in the thick ascending limb of the Henle's loop and in the distal convoluted tubule and lower binding levels (2-5 X 10(-18) mol mm-1) in the collecting tubule whereas specific binding could not be detected in the proximal tubule and in the thin segments of the Henle's loop. In the medullary thick ascending limb, Scatchard analysis of specific [125I]glucagon binding indicated an apparent equilibrium dissociation constant of 2.4 nM. The stereospecificity of binding sites in medullary thick ascending limbs and medullary collecting tubules, was assessed by competition experiments using unlabelled glucagon, enteroglucagon and unrelated hormones (vasopressin, calcitonin, parathyroid hormone and insulin); in both segments, glucagon was more active than enteroglucagon in displacing labelled glucagon from its tubular binding sites, whereas all other hormones tested were inactive. These results indicate that tubule binding sites might be the physiological receptors for glucagon involved in adenylate cyclase activation.

Animals↗
PubMed1984

Examination of the oxidase function of the b-type cytochrome in human polymorphonuclear leucocytes.

The spectral properties of a particulate fraction of human polymorphonuclear neutrophils capable of oxidizing NADPH were studied before and after depletion of myeloperoxidase by KCl treatment. Difference spectra (dithionite reduced minus oxidized) at 77 K of non-extracted particles showed peaks of a b-type cytochrome at 556, 527 and 425 nm and of myeloperoxidase at 636 and 474 nm. Extraction of myeloperoxidase led to a 4-5-fold increase in the size of the cytochrome b peaks. In non-extracted particles, the CO-reduced spectra at 77 K revealed a typical CO-reduced myeloperoxidase complex with new peaks at 625-630 and 462 nm, and a limited shift of the Soret band of reduced cytochrome b from 425 to 424-423 nm. The same shift was observed for cytochrome b in extracted particles. Photoirradiation of the CO-dithionite-reduced particles resulted in a back shift of the CO-reduced peaks to their original positions in the reduced spectrum. Concomitantly, the size of the peaks both for myeloperoxidase and cytochrome b was increased, indicating photoreduction. Cytochrome b and myeloperoxidase in neutrophil particles were poorly reduced by NADPH; reduction occurred upon photoirradiation. FAD and FMN added to particles in the presence of NADPH were photoreduced concomitantly with cytochrome b. Addition of phorbol myristate acetate to intact neutrophils in the presence of glucose resulted in CO- and cyanide-insensitive respiration, accumulation of O-2, and also in reduction of cytochrome b. The lag required to reach the steady-state production of O-2 was equal to the lag required for cytochrome b to reach a plateau of reduction. The data are consistent with the idea that cytochrome b in neutrophils might belong to a branched pathway that is not rate-limiting in the cyanide-resistant respiration of the neutrophils.

Carbon Monoxide↗
PubMed1984

Kallikrein along the rabbit microdissected nephron: a micromethod for its measurement. Effect of adrenalectomy and DOCA treatment.

Active and inactive kallikrein were measured along the rabbit microdissected nephron. A sensitive and specific micromethod for the measurement of kininogenase activity was developed in order to quantify kallikrein in pieces of tubule as small as 0.3-0.5 mm. Our study confirms that active and inactive kallikrein are located to the connecting tubule (CNT). The effects on renal kallikrein of a chronic DOCA treatment and of adrenalectomy were studied. Urinary excretion of kallikrein was also monitored. After DOCA treatment, active kallikrein increased in the tubule and in urine but inactive kallikrein did not significantly change. Adrenalectomy decreased by 50% active and inactive contents of CNT, as well as reduced the excretion of total kallikrein. Kallikrein content in CNT was also measured in adrenalectomized rabbits 3 h after a single injection of either aldosterone (10 micrograms) or dexamethasone (100 micrograms). After either aldosterone or dexamethasone injections, kallikrein activities were not restored, whereas in the same animals Na-K-ATPase activity which was depressed on cortical and medullary collecting tubules after adrenalectomy returned toward normal values. These data indicate that kallikrein synthesis and activation are influenced by adrenal hormones. Renal kallikrein is, however, regulated at a much slower rate than Na+-K+-ATPase. This may suggest an indirect rather than direct action of corticosteroid hormones on kallikrein.

Adrenal Cortex Hormones↗
PubMed1984

Metabolic CO2 production by isolated single pieces of rat distal nephron segments.

A method is described which allowed in-vitro measurements of metabolic CO2 production from [U-14C]-substrates by single pieces of kidney tubules. The tubules were isolated by microdissection from collagenase treated rat kidneys. Single pieces of various distal nephrons portions were incubated in 1 microliter of bicarbonate free minimum essential medium containing the required [U-14C]-substrate (about 0.2 mu Ci per sample), and the 14CO2 produced was continuously trapped into a 2-microliter KOH droplet. The KOH droplets were replaced every 30 min. Metabolic CO2 production from the labelled substrate used was calculated as picomoles CO2 per mm of tubular length per minute, by dividing the KOH radioactivity by the specific radioactivity per carbon of the substrate present in the incubate [( U-14C] plus cold substrate concentrations). Under these conditions, it was established that single pieces of tubule could sustain almost constant CO2 production for at least 2 h at 31 degrees C. Experiments testing four different conditions with five to six replicate samples per condition were performed in order to compare oxidative metabolism in medullary (MAL) and cortical (CAL) thick ascending limbs, medullary (MCT) and cortical (CCT) collecting tubules and, in a few instances, proximal convoluted tubules (PCT) and early distal convoluted tubules (DCT).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed1984

Plasma antidiuretic hormone levels and kidney responsiveness to vasopressin in the jerboa, Jaculus orientalis.

The plasma antidiuretic hormone (ADH) concentration and the kidney medulla responsiveness to vasopressin were measured in adult jerboas ( Jaculus orientalis) in different states of hydration. In 15 jerboas adapted to 30 degrees and fed a dry diet, the average ADH concentration in blood plasma was 479 +/- 59 pg/ml, as measured by a radioimmunoassay. About 6 hr after receiving a 5% body wt water load by gavage, the plasma ADH concentration fell to 130 +/- 30 pg/ml in the 5 jerboas still producing hypertonic urine (1022 +/- 267 mosmol/liter) and to 41.5 +/- 8.4 pg/ml in the 6 jerboas producing hypoosmotic urine (157 +/- 6 mosmol/liter). In vitro biochemical experiments were performed on the kidney medullas from two groups of 5 jerboas fed a dry diet (group I) or a water-enriched diet (group II), respectively, for 4 to 7 weeks. Compared to group II, group I animals exhibited (a) higher plasma ADH values, 372 +/- 86 versus 76 +/- 25 pg/ml; (b) higher urine osmolarities (3817 +/- 638 versus 647 +/- 90 mosmol/liter); (c) some decrease in [3H]lysine-vasopressin (LVP) binding capacity to kidney membrane fractions (maximal binding: 0.4 versus 0.6 pmol [3H]LVP bound/mg protein); d) decreased adenylate cyclase responses to arginine-vasopressin, lysine-vasopressin, and oxytocin in kidney membrane fractions; and (e) weaker adenylate cyclase responses to arginine-vasopressin in microdissected pieces of the medullary thick ascending limb of Henle's loop. The values found for (a) the dissociation constant of [3H]lysine-vasopressin binding to membranes (KD); (b) adenylate cyclase sensitivity to the three neurohypophyseal hormones (KA); and (c) adenylate cyclase sensitivity to arginine-vasopressin (KA) in medullary collecting tubules and medullary thick ascending limbs are similar in the two groups of jerboas and roughly comparable to those previously reported for the rat kidney medulla. The reduced maximal adenylate cyclase responses to vasopressin in the jerboas fed a dry diet might indicate some physiological "down regulation" of the number of vasopressin-specific receptors in the kidney as a result of the huge ADH concentration present in blood plasma under these conditions. However, this desensitization is not sufficient to account for the production of hypoosmotic urine in spite of the relatively high ADH plasma levels which persisted after acute overhydration.

Adenylyl Cyclases↗
PubMed1984

Inhibition of alpha 2-adrenergic agonists on AVP-induced cAMP accumulation in isolated collecting tubule of the rat kidney.

A microradioimmunoassay for cAMP was developed in order to analyse the effects of alpha-adrenergic agonists on vasopressin (AVP)-induced cAMP cell accumulation in single pieces of microdissected medullary (MCT) and cortical (CCT) rat collecting tubules. Under the experimental conditions chosen (4 min of incubation in the presence of a phosphodiesterase inhibitor), no cAMP could be detected either in the bathing solution or in non-stimulating samples of tubule. In MCT, 10(-6) M AVP stimulated cAMP generation up to 128.3 +/- 9.0 (SEM) fmoles per mm of tubule per 4 min, N = 11. The response was dose-dependent with a KA value below 10(-10) M AVP. The addition of norepinephrine (NE) (10(-5) M in the presence of propranolol) suppressed the larger part of the response to AVP (from 92% with 2 X 10(-11) M AVP to 76% with 10(-6) M AVP); the addition of 10(-7) M NE still reduced by 59% the MCT response to 10(-10) M AVP (26.2 +/- 5.9 vs. 64.0 +/- 6.4 fmoles/mm, N = 3). In CCT, 10(-5) M NE reduced by 84% the cAMP generation induced by 10(-10) M AVP (8.8 +/- 2.0 vs. 54.2 +/- 3.5 fmoles/mm, N = 3). This inhibitory action of NE against the AVP effect in CCT was mimicked by 10(-7) M clonidine; in MCT it was suppressed by phentolamine and yohimbine, but not by prazosin, suggesting that alpha 2-adrenoreceptors are involved. On the other hand, the addition of the alpha-agonists to the incubation solution produced no inhibition of the cAMP cell accumulations induced by glucagon, calcitonin and isoproterenol in CCT, or glucagon in MCT, an observation demonstrating that alpha 2-adrenergic agonists selectively inhibit vasopressin-dependent cAMP generation by these nephron segments.

Adrenergic alpha-Agonists↗
PubMed1984

Na+ and K+ cell concentrations in collagenase-treated rat kidney tubules incubated at various temperatures.

Na+ and K+ cell contents were measured in single pieces of tubule (0.4-0.8 mm/sample) micro-dissected from the outer medulla of collagenase-treated rat kidney tissue. Extracellular cations were washed out by rinsing the tubules in ice-cold choline-chloride solution. Na+ and K+ cell contents were measured by emission flame microphotometry after appropriate treatment of the samples. Tubular volumes were calculated from photographic pictures taken before (at 4 degrees C) and after incubation of the samples. Medullary collecting tubules (MCT) and medullary thick ascending limbs of Henle (MAL) were used in this study. When kept at 4 degrees C for 2 h or more, Na+ and K+ concentrations (meq/l cell volume) were 86.3 and 30.6, respectively, in MCT and 16.2 and 94.3, respectively, in MAL. After about 5 min of incubation at 30 degrees C, MCT samples inverted their cation contents up to new steady-state concentrations (Na+ 17.4 and K+ 97.5). During incubation, the volume of MCT samples decreased slowly and in an exponential way, the rate of which was highly temperature dependent. Na+ and K+ cell concentrations in such incubated MCT samples, however, remained fairly constant between 20 and 37 degrees C. In contrast, when MAL samples were incubated at 30 degrees C, Na+ and K+ concentrations (15.9 and 90.4, respectively) remained equal to those measured at 4 degrees C and no change in volume was observed in MAL samples.

Animals↗
PubMed1984

Ontogenesis of hormone-dependent adenylate cyclase in isolated rat nephron segments.

Ontogenesis of hormone-dependent adenylate cyclase (AC) was investigated in rat kidney by single tubule microassay between two days postnatal and adulthood. This approach allowed us to analyze the kinetics of vasopressin-sensitive AC maturation in its tubular target sites, namely the thick ascending limb and collecting tubule. It was also possible to compare in a single segment--the thick ascending limb--the kinetics of AC ontogenesis for three hormones-- vasopressin, calcitonin, and parathyroid hormone. The results show that 1) 2 days after birth AC is still poorly responsive to vasopressin, especially in the thick ascending limb. By contrast, this segment exhibits marked AC responses to calcitonin and parathyroid hormone. 2) For a given hormone, the kinetics of AC ontogenesis depends on the segment in which the receptor-enzyme complex is located. 3) For a given segment, the pattern of AC maturation is specific for each hormone. These data indicate that the process of tubular AC maturation cannot be accounted for simply by an increase in basolateral membrane area or by the synthesis of new catalytic units. More specific mechanisms must be involved that regulate independently the synthesis of each kind of hormone receptor and/or its coupling to cyclase.

Adenylyl Cyclases↗