[Calciumdependent mechanisms in vasopressin regulation of osmotic water permeability in the mouse kidney collecting duct cells].

In the study, the role of PKC and Ca++ in vasopressin regulation of the plasma membrane water permeability was studied in the cells of the mouse kidney collecting duct. Coefficient of osmotic water permeability of total cell surface (Pf) was calculated from the initial rate of cell swelling following the osmotic shock caused by changing the medium osmolarity from isotonic to hypotonic (300 mOsm to 200 mOsm). Desmopressin (dDAVP 1 nM) increased the Pf in hydrated mice from 168.4 +/- 11.8 microm/s up to 231.3 +/- 14.7 microm/s. The Ca++ chelator BAPTA prevented the desmopressin-induced increase in water permeability. Inhibition of PKC (Ro-31-8220 0.1 microM) also abolished the desmopressin-stimulated increase of plasma membrane water permeability, whereas inhibitor of PKC alone did not suppress the stimulation of the water permeability by db-cAMP. The PKC activity and calciumdependent second messengers seem to be important for regulation of water permeability by vasopressin.

[Water permeability of the OMCD and IMCD cells' basolateral membrane under the conditions of dehydration and dDAVP action]. / Vodnaia pronitsaemost' bazolateral'noi membrany kletok sobiratel'nykh trubok naruzhnogo i vnutrennego mozgovogo veshchestva pochki krys v usloviiakh degidrtatsii pri deistvii desmopressina.

Water permeability of the basolateral membrane was estimated in isolated fragments of OMCD or IMCD in the Wistar rats. Apical surface of the fragments was blocked with oil injected into the lumen. Apparent water permeability coefficient (Pf) was measured by the rate of epithelium swelling following transition from hypertonic to isotonic medium (600 mOsm to 300 mOsm). Water deprivation caused significant increase in the Pf value in OMCD and IMCD fragments. Desmopressin (10(-8) M) increased water permeability in hydrated rats both in OMCD and IMCD. Mercury chloride decreased the Pf and abolished the effect of desmopressin in reversible manner. Estimation of aquaporins 2, 3, 4 mRNA content in the renal medulla was performed by semi-quantitative RT-PCR. Content of AQP4 and AQP2 mRNA in dehydrated animals was significantly higher than in hydrated ones both in outer medulla and inner medulla. Expression of AQP3 increased during dehydration only in the inner medulla. The findings reveal that water permeability of OMCD and IMCD can be increased by physiological stimuli, e.g. water deprivation. The activation of gene expression of the key elements of vasopressin signal system seems to contribute to this reaction.

[Vasopressin-dependent water permeability of the basolateral membrane of the kidney outer medullary collecting duct in postnatal ontogenesis in rats]. / Vazopressinzavisimaia vodnaia pronitsaemost' bazolateral'noi poverkhnosti sobiratel'nykh trubok naruzhnogo mozgovogo veshchestva pochki krysy v postnatal'nom ontogeneze.

Kidneys of new-born animals are resistant to arginine vasopressin (AVP). The ability of the hormone to regulate water permeability of the collecting duct can be seen from weaning period, probably due to the maturation of the intracellular signaling pathway. The purpose of the present work was to investigate the effect of V2 receptor agonist dDAVP on the water permeability of OMCD basolateral membrane in 10-, 22- and 60-day old Wistar rats. We also estimated ontogenetic gene expression of AQP2, AQP3, AQP4 and V2 receptor. Osmotic water permeability (Pf) of the basolateral membrane of microdissected OMCD was measured under control conditions and after incubation with the agonist V2 receptor desmopressin (dDAVP; 10(-7) M). Water permeability in 10- and 22-day old rats under control conditions were significantly higher than in adults. Desmopressin stimulated significant increase of this parameter in 22-day old pups (Pf = = 125 +/- 4.85; Pf = 174 +/- 8.2 microns/s, p < 0.001) and adult rats (Pf = 100.5 +/- 7.38; Pf = 178.8 +/- 9.54 microns/s, p < 0.001). Osmotic water permeability of the OMCD basolateral membrane in 10-day old rats does not depend on dDAVP (Pf = 172.5 +/- 23.8; Pf = 164.8 +/- 34 microns/s). With the RT-PCR, we observed a gradual increase of AQP2 and V2 receptor genes expression during postnatal ontogenesis. The gene expression of AQP3 and AQP4 remained unchanged during postnatal ontogenesis. In general, the water permeability of the OMCD basolateral membrane of rats can be stimulated by AVP since the 22nd day of postnatal life. The water permeability of the OMCD basolateral membrane under control conditions gradually decreased during postnatal development, while gene expression of AQP3 and AQP4 was unchanged. The mechanism of this decrease remains to be established.

Effect of dDAVP on basolateral cell surface water permeability in the outer medullary collecting duct.

We report a novel approach for assessing the volume of living cells which allows quantitative, high-resolution characterization of dynamic changes in cell volume while retaining the cell functionality. The aim of this study was to evaluate the short-term effect of vasopressin on basolateral cell surface water permeability in the outer medullary collecting duct (OMCD). The permeability of the basolateral cell membrane was determined in the tubules where the apical membrane was blocked with oil injected into the lumen. The apparent coefficient of water permeability (Pf) was evaluated by measuring the cell swelling after the step from hypertonic to isotonic medium (600 mosm to 300 mosm). Desmopressin (dDAVP) induced an increase of the basolateral Pf from 113.7+/-8.5 microm/s in control cells to 186.6+/-11.4 mum/s in micro-dissected fragments of the OMCD incubated in vitro (10(-7) M dDAVP, 30 min at 37 degrees C) (P<0.05). Mercury caused pronounced inhibition of basolateral water permeability (26.0+/-6.9 microm/s; P<0.05). The effect of mercury (1.0 mM HgCl2) was reversible: after washing the fragments with PBS for 20 min, Pf values were restored to the control levels (125.0+/-9.5 microm/s). The results of the study indicate the existence of a mechanism controlling the osmotic water permeability of the basolateral cell membrane in the OMCD epithelium.

[Effect of dehydration and dDAVP on water permeability of basolateral membranes of epithelial cells in the kidney collecting tubules]. / Vliianie degidratatsii i dDAVP na pronitsaemost' dlia vody bazolateral'noi membrany kletok épiteliia sobiratel'nykh trubok pochki.

Water permeability of the outer medullary collecting duct's (OMCD) basolateral membrane was determined in vitro in the tubules isolated from hyperhydrated or dehydrated Wistar rats. Oil was injected into the lumen to block apical membrane water permeability. OMCD fragments underwent a hypoosmic shock (600/300 mOsm) and epithelial cells volume increased ad recorded with a digital camera. The latter's rate was used to calculate apparent water permeability of the membrane (Pf). Treatment of the tubules with Hg2Cl2 suppressed the water permeability. Water deprivation and dDAVP induced an increase in the basolateral water permeability. The data obtained suggest that the water permeability of the OMCD basolateral membrane may be stimulated by vasopressin and water deprivation.