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Biomedical subjects

F Morel

Publications and source records attributed to F Morel.

At least 217 records · Page 12Linked to original sources
PubMed1978

Vasopressin-dependent adenylate cyclase activities in the rat kidney medulla: evidence for two separate sites of action.

This study demostrates the existence of an adenylate cyclase sensitive to vasopressin in the medullary portion of the rat thick ascending limb. Maximal adenylate cyclase stimulations achieved in that segment (31-fold) were higher than those obtained in collecting tubules from the same rats (22-fold). From comparisons of absolute maximal responses it can be calculated that thick ascending limbs account for about 80% of the response to vasopressin of a kidney medulla homogenate. The apparent Km value of adenylate cyclase activation (from 10(-9)-2 x 10(-8) M) in thick ascending limbs was higher in each experiment than that simultaneously measured in the collecting tubules from the same rats (2 x 10(-10)-3 x 10(-9) M). Such a lower sensitivity is probably not due to a greater hormone degradation by the thick ascending limb samples. Experiments using structural analogues of the oxytocin series ([deamino-6-carba]oxytocin and vasotocin) did not give evidence for different vasopressin receptors in the thick ascending limb and the collecting tubule. A step beyond the hormone-receptor interaction, thus, must account for the different patterns of adenylate cyclase response to vasopressin of these two segments.

Adenylyl Cyclases↗
PubMed1976

Functional segmentation of the rabbit distal tubule by microdetermination of hormone-dependent adenylate cyclase activity.

Rabbit distal convoluted tubules (DCT) microdissected from collagenase-treated kidneys were observed to contain up to four portions of a different appearance under stereomicroscopic examination: (1) a DCTa portion (generally very short), located right after the macula densa (MD) and resembling the portion of the limb (CAL) located before the MD; (2) a constant, "bright" portion, DCTb; (3) a constant, "granular" DCTg portion which, in most DCT, is connected to a portion of the collecting tubule of a similar "granular" appearance (CCTg); (4) many DCT having contacts with the kidney capsule in the superficial cortex were observed to contain an additional portion of a "light" appearance, DCTl, resembling the portion of the collecting tubule (CCTl) to which these superficial DCT are always branched. The hormone-dependent adenylate cyclase (AC) contained in these different portions was investigated by sectioning microdissected distal structures into successive samples according to the above-mentioned criteria, and by measuring with the help of a previously described micromethod, the enzyme activity contained in each single sample under one of the following conditions: control, parathyroid hormone. (PTH l U/ml), vasopressin, (AVP 10(-6)M), isoproterenol (10(-6)M), fluoride (5 X 10(-3)M). Highly significant and reproducible AC stimulations by these hormones were obtained for the following portions, respectively: DCTa, DCTg and CCTg with PTH; DCTl and CCTl with AVP; DCTg, CCTg and CCTl with isoproterenol. From these data, it is concluded that (a) the distal convoluted tubule can no longer be regarded as a single well-defined functional structure; (b) DCTa is actually a short CAL portion extending beyond MD, (c) DCTg and CCTg are two portions of a same functional segment; (d) similarly, DCTl belongs to the functional segment mainly constituted by CCTl; and, finally, (e) DCTb is the only functional segment which is entirely located in the distal convoluted tubule, i.e., included between the macula densa and the first branching with another tubule.

Adenylyl Cyclases↗
PubMed1976

Distribution of calcitonin-sensitive adenylate cyclase activity along the rabbit kidney tubule.

The adenylate cyclase [ATP pyrophosphatelyase (cyclizing), EC 4.6.1.1] sensitivity to salmon calcitonin in 11 different segments of the rabbit nephron was investigated using a micromethod for enzyme activity measurements in samples, each containing a single piece of tubule. The required segments were isolated by microdissection from collagenase-treated rabbit kidneys. The results were expressed as femtomoles of adenosine 3':5'-cyclic monophosphate formed per mm of tubular length per 30 min of incubation time. In the presence of 0.1 mug/ml of synthetic salmon calcitonin, it was found that eight segments exhibited no hormonal sensitivity whereas maximal responses were induced in three segments, the "bright" portion of the distal convoluted tubule, the cortical and the medullary portions of the thick ascending limb of the loop of Henle (stimulated over control activity ratios were 32, 11, and27). The very high sensitivity to calcitonin of the adenylate cyclase contained in these three segments (0.01 ng/ml of salmon calcitonin inducing a 2-fold stimulation; half-miximal stimulation corresponding to about 0.3 ng/ml of salmon calcitonin) suggests that the distal convoluted tubule, as well as th cortical and medullary portions of the thick ascending limb of the loop of Henle represent physiological target structures of calcitonin action within the kidney.

Adenylyl Cyclases↗
PubMed1975

Catecholamine sensitive adenylate cyclase activity in different segments of the rabbit nephron.

The sensitivity to catecholamines of the adenylate cyclase (AC) activity contained in single tubule samples was investigated on 10 different well defined segments, isolated by microdissection from collagenase treated rabbit kidneys. No responsiveness to isoproterenol (10(-6) M) was observed in the proximal tubule (convoluted and straight portions), the thin descending and thick ascending limbs of the loop of Henle, and the first ("bright") portion of the distal convoluted tubule (DCTb); in contrast high responses (stimulation factors: 4 to 6 fold) were obtained in the second ("granular") portion of the distal convoluted tubule (DCTg), as well as in both the "granular" (CCTg) and the "light" (CCTl) portions of the cortical collecting tubule. In absolute value, however, the CCTl response was definitely lower than those measured in DCTg and CCTg, as is its control activity. In the medullary portion of the collecting tubule, the AC response to isoproterenol was rather poor both in absolute and relative terms. Dose-response curves measured on DCTg samples indicated a threshold response with an isoproterenol concentration below 10(-8) M; half maximal effect corresponded to about 3 x 10(-8) M. CCTl sensitivity to isoproterenol was of the same order of magnitude. Isoproterenol as well as norepinephrine effects in DCTg and CCTl were completely suppressed by 10(-4) M propranolol, indicating that the observed AC stimulation was mediated via receptors of the beta type. In beta blocked CCTl, 10(-6) M norepinephrine did not inhibit vasopressin-induced AC stimulation; in the presence of 10(-6) M norepinephrine, 10(-4) M phentolamine resulted in no additional AC stimulation in DCTg and CCTl; these data suggest the absence of alpha receptors inhibiting AC activity in these structures. In DCTg, AC stimulation induced either by 10(-6) M isoproterenol or by 1 U/ml PTH were observed to be additive when the two hormones were given together. The presence of catecholamine-dependent AC activity in three distal portions of the rabbit nephron is discussed in relation to its possible physiological implications.

1-Propanol↗
PubMed1975

Transient current changes and Na compartimentalization in frog skin epithelium.

Experimental conditions are described in which transient and positive current responses across isolated frog skin epithelia can be elicited by sudden addition of Na and Li ions (2--40 mM) in the outer bathing solutions. Subsequent return to outer Na (or Li) free conditions produce similar transient current changes but in the opposite direction. Analysis of the curve responses shows that the transient component of each curve is best described by a single, fast exponential term equation in case of Na addition to preparation unpoisonned with ouabain. In contrast, an equation including two exponential terms (a fast and a slow one) is required to fit the curve responses observed across ouabain treated epithelia or if Li is added outside. The transient responses were not significantly altered by substituying Cl for SO4(2)-anions. They were completely prevented by Amiloride (5-10(-5) M), increased by oxytocin (20 mU/ml) and markedly dependent upon the outer Na concentration. Interpreted in term of compartmental analysis, these observations suggest that a) the frog skin epithelium contains 2 separated but communicating compartments having different degrees of accessibility from outside; b) only that compartment filling at a fast rate (0.5 min) is involved in the transepithelial Na transport; c) the other one, filling at a rate of 4 to 7 min, is resplenished only under conditions where the basal pump system has a reduced activity. Tentative localization of these compartment is proposed.

Amiloride↗
PubMed1975

Na and K movements across the membranes of frog skin epithelia associated with transient current changes.

The ionic composition of the current crossing each membrane of the frog skin epithelia during a) the positive and transient current responses elicited by sudden addition of Na ions to the outer Na free medium b) the negative and transient current responses observed when Na loaded preparations are suddenly exposed to outer Na free solution was determined using isotopic techniques. It is shown that Na ions carry the current across the outer membrane while K ions are mainly involved in the transfert of charges across the inner membrane. The amount of Na accumulated by the epithelial cells during the responses is correlated to the area under the transient part of the current responses. Determinations of 24Na uptake at different time of these transient positive responses show that the unidirectional Na influx across the outer membrane decreases as a function of time. It is suggested that the intracellular Na concentration might control the Na uptake mechanism across the outer membrane. During the negative responses, the Na efflux into the outer medium is highly correlated, either in time course or magnitude, to the current response. Both Na efflux and negative current are sensitive to amiloride, suggesting that the mechanism of Na uptake by the frog skin also is able to promote Na movement out of the epithelial cells.

Amiloride↗
PubMed1975

Vasopressin dependent adenylate cyclase in single segments of rabbit kidney tubule.

AVP dependent adenylate cyclase activity was measured in single pieces of 8 different tubular segments isolated from collagenase treated rabbit kidneys. High responses were observed in all the tested portions of the collecting tubule, that is its cortical branched part (BCT), its cortical straight part (CCT) and its outer medullary part (MCT). Dose response curves indicated in CCT: 2 fold threshold stimulation at 10(-11) M AVP, 27 fold stimulation at 10(-6) M AVP, half maximal stimulation at about 10(-9) M AVP. Both the medullary (MAL) and, to a lesser extent, the cortical (CAL) portions of the thick ascending limb were also observed to contain AVP sensitive adenylate cyclase (for MAL: 2 fold threshold stimulation at 10(-9) M AVP, 9 fold stimulation at 10(-7) M AVP, half maximal stimulation at 5 X 10(-9) M AVP). In contrast, nearly no responsiveness to AVP was observed in the proximal convoluted tubule, in the thin descending limb of the loop and in the distal convoluted tubule (DCT). The limited response obtained in DCT (which is a structure generally considered as a target site for AVP) as well as the clearcut effect elicited by AVP in MAL (the functioning of which is not known to be controlled by ADH) were expected observations; their possible physiological implications will be discussed.

Adenylyl Cyclases↗
PubMed1975

[Vasopressin-stimulated adenyl cyclase activity in the ascending portions of rabbit kidney nephron loops].

The adenylate-cyclase activity contained in the successive segments of the loop of Henle was measured using single tubular pieces isolated by microdissection. Vasopressin (10 (-6) M) had no significant effect on either the pars recta or the thin descending limb; whereas, it stimulated the enzyme contained in the thin ascending limb (8.9 fold as a mean value) and that contained in the medullary portion of the large ascending limb (14.7 fold).

Adenylyl Cyclases↗
PubMed1975

Adenylate cyclase activity along the rabbit nephron as measured in single isolated segments.

A method is described, which allows adenylate cyclase activity measurement in single pieces of various nephron segments. Tubular samples of 0.5 to 2 mm length were isolated by microdissection from collagenase treated slices of rabbit kidney. A photograph of each piece was taken in order to measure its length. After a permeabilisation treatment involving preincubation in a hypoosmotic medium and a freezing step, each sample was incubated for 30 mm at 30 degrees C in a medium containing high specific (alpha-32-P)-ATP 3-10-4 M, final volume 2.5 mu 1. The (32P)-cAMP formed was separated from the other labelled nucleotides by filtering the incubate on a dry aluminium oxide microcolumn, 3H cAMP was added as a tracer for measuring cAMP recovery. The sensitivity of the method was found to be a few fentomoles (10-15 M) cAMP. cAMP generation increased linearly as a function of the incubation time up to more than 30 min, and as a function of the length of the segment used. Control and fluoride (5 mM) stimulated adenvlate cyclase activities were measured in the following segments of the nephron: early proximal convoluted tubule (PCT), pars recta of the proximal tubule (PR), thin descending limb of the loop (TDL), cortical portion of the thick ascending limb (CAL), distal convoluted tubule (dct), first branched portion of the collecting tubule (BCT), further cortical (CCT) and medullary (MCT) portions of the collecting tubule. Mean control adenylate cyclase activity varied from 7 (PR) to 75 (BCT) fmoles/mm/30 min. Flouride addition resulted in a 10 (BCT) to 50 (PR) fold increase in enzyme activity. Series of replicates gave a scatter equal to plus or minus 20% (S.D. as a per cent of the mean). The method described appears to be suitable to determine which nephron segments contain hormone-dependent adenylate cyclase.

Adenylyl Cyclases↗
PubMed1975

PTH sensitive adenyl cyclase activity in different segments of the rabbit nephron.

PTH sensitive adenylate cyclase activity was measured in 9 different segments of the nephron, isolated by microdissection from collagenase-treated rabbit kidney slices. The enzyme of the following segments was stimulated by PTH, 1 U/ml: PCT. (proximal convoluted tubule); PR (pars recta); CAL (cortical portion of the thick ascending limb); DCT (distal convoluted tubule); BCT (first, branched portion of the collecting tubule); the segments which did not respond to PTH were: TDL (thin descending limb): MAL (medullary portion of the thick ascending limb); CCT (cortical portion of the collecting tubule distally adjacent to BCT); MCT (collecting tubule from the outer medulla). PTH sensitive adenylate cyclase per mm tubule in PR was half that measured in PCT. Half maximal stimulation corresponded to 50-100mm U/ml PTH (1-2 times 10-8M) in both PCT and PR, and to about 350 mm U/ml in CAL. PTH (1 U/ml) stimulation factors ranged from 5 to 60 depending on the structures. It is concluded that in addition to PCT and PR, CAL and BCT might be target structures involved in the physiological actions of PTH on the kidney.

Adenylyl Cyclases↗