Locally formed dopamine modulates renal Na-Pi co-transport through DA1 and DA2 receptors

The involvement of dopamine (DA) receptor subtypes in regulation of renal phosphate transport by DA, either exogenous or locally synthesized from L-dihydroxyphenylalanine (L-dopa) was evaluated in opossum kidney (OK) cells with proximal tubular phenotype. DA synthesis from L-dopa by OK cells was abolished by carbidopa and benserazide, two dissimilar inhibitors of aromatic L-amino acid decarboxylase. L-Dopa stimulated cyclic AMP generation and inhibited Na-dependent Pi uptake, and these effects were abolished by carbidopa and benserazide. The effects of L-dopa or DA on cyclic AMP generation and on Na-Pi co-transport were mimicked by SKF 38393, a DA1 receptor agonist, and were potentiated by S-sulpiride, a DA2 receptor antagonist. Bromocriptine, a DA2 receptor agonist, blunted in a pertussis toxin-dependent manner parathyroid hormone (PTH)-induced cyclic AMP generation and inhibition of Pi uptake. In contrast with PTH, neither L-dopa nor DA affected significantly the cytosolic calcium concentration. These results support the involvement of DA1 and DA2 receptors, positively and negatively coupled into adenylate cyclase respectively, in modulation of renal phosphate transport.

Evidence for Na-K-Cl cotransport in alveolar epithelial cells: effect of phorbol ester and osmotic stress

We have investigated the presence of Na-K-Cl cotransport in alveolar type II cells using uptake of 86Rb. Several data support the presence of a Na-K-Cl cotransport in these cells. First, a large fraction of ouabain-resistant 86Rb uptake was inhibited by bumetanide and furosemide. Second, bumetanide-sensitive 86Rb uptake required the presence of Na+ and Cl- in the incubation medium; dependency on extracellular Na+ and K+ was hyperbolic, with a Km of 14.6 mM and 8.3 mM, respectively, while dependency on extracellular Cl- was sigmoidal, which suggests a 1:1:2 stoichiometry. Third, a fraction of amiloride-insensitive 22Na influx was deeply inhibited by bumetanide. 22Na influx was dependent on the presence of extracellular K+ and Cl-. Since Na-K-Cl activity dramatically decreased with time in culture, further characterization of the cotransport on polarized cells could not be performed. The phorbol ester PMA inhibited Na-K-Cl cotransport in a time- and concentration-dependent manner. This inhibition was mimicked by oleoylacetylglycerol, dioctanoylglycerol, and the diacylglycerol kinase inhibitor R59022, and was reversed by an antagonist of PKC, staurosporine. Since the Na-K-Cl cotransport has been reported to be involved in cell volume regulation, we investigated its modulation by changes in extracellular osmolarity. Na-K-Cl activity was increased after a two-step procedure: swelling in hypotonic medium followed by shrinking in hypertonic medium. Under these conditions, cotransport activity increased whenever PKC activity was up- or downregulated, which suggests that the cell volume-induced modulation of the cotransport is independent from the PKC activity. Though we were not able to determine the polarity of the cotransport, it may also be involved in the absorptive function of alveolar type II cells, and would provide an alternate pathway for sodium entry.

Lipopolysaccharides stimulate Na-dependent transport in alveolar cells and protect against oxidant injury

We have evaluated the effect of lipopolysaccharides (LPS), endotoxins from gram negative bacteria, on sodium-coupled amino acid and phosphate transport by alveolar epithelial type II cells and on their alteration induced by oxidants. Alveolar type II cells were obtained by enzymatic digestion of rat lung and grown for 24 h prior to incubation with LPS and then exposed or not exposed to H2O2 (2.5 mM; 20 min). LPS (10 micrograms/ml, 24 h) induced a significant increase in the Na-dependent component of alanine and phosphate uptake while they decreased Na,K-ATPase activity measured by ouabain-sensitive 86Rb influx. We showed that this stimulatory effect i) was independent from macrophage products since it was not mimicked either by supernatant of LPS-treated alveolar macrophages or by pretreatment with tumor necrosis factor and/or interleukin 1 and ii) was dependent on protein synthesis since it was abolished by protein synthesis inhibitors cycloheximide and actinomycin D. Moreover, LPS blunted H2O2-induced decrease of Na-dependent alanine and phosphate uptake. This protective effect of LPS against H2O2 injury i) was independent of macrophage products, ii) was abolished by cycloheximide, and iii) was not associated with either changes in extracellular H2O2 clearance or catalase and glutathione peroxidase activities. We conclude that, in alveolar type II cells, LPS stimulate sodium-coupled transport by a process involving protein synthesis and partially prevent H2O2-induced decrease of Na-coupled transport without discernible change in antioxidant activities.

[Isolation of an acid-alcohol resistant bacillus (BAAR) in the febrile HIV infected patients: Mycobacterium tuberculosis (MT) or Mycobacterium avium complex (MAC)?]

The detection of BAAR in HIV infected patients with CD4 < 100/mm3 and with an infectious syndrome urge on beginning an effective treatment against Mycobacterium tuberculosis and/or Mycobacterium avium Complex, before the results of the culture are known. Our purpose was to search clinical and biological features to angle directly the diagnosis towards a tuberculosis or not, and to start the most suitable treatment. This retrospective study, from 1986 to 1993, stated on 54 patients who had at least one sample with positive BAAR (blood, marrow, stools, sputum or urine cultures). From these cultures, MAC was isolated on 37 patients and BK on 17. The both groups were similar for age, sex, risk factor, number of opportunistic infections, delay between the date of AIDS and the discovery of a positive BAAR, and Ag p24. However, a significant difference in favor of a MAC disease exists regarding about: disseminated infections (92% vs 53%), digestive troubles (57% vs 23.5%), anterior or concomitant CMV infection (49% vs 9%), isolation of BAAR in blood culture (54% vs 20%) or in stools culture (76% vs 33%), leucopenia (2850/mm3 +/- 1520 vs 4124/mm3 +/- 2232), anémia (Hb 9.1 g/dl +/- 1.5 vs 10.1 g/dl +/- 1.6). The univariated analysis of results allowed us to conclude that the presence of one among those parameters must induce the prescription of a suitable treatment against MAC.

Oxygen metabolites modulate sodium transport in gerbil middle ear epithelium: involvement of PGE2

The middle ear epithelium and respiratory epithelia share basic properties such as homeostasis of air-filled cavities and mucociliary clearance toward the pharynx. With the middle ear SV40-transformed (MESV) cell line, we used the short-circuit current (Isc) technique to investigate changes in ion transport induced by oxidants. Xanthine and xanthine oxidase on the basal side of the monolayers dramatically increased Isc up to 50%. This effect was not affected by superoxide dismutase or mannitol, but could be blunted by catalase or 1,3-dimethyl-2-thiourea. Increasing concentrations of H2O2 from 10(-5) to 5 x 10(-4) M produced a dose-dependent increase in Isc from 0.26 +/- 0.16 up to 4.21 +/- 0.43 microA/cm2 (P < 0.05, n = 5). Concentration of half-maximal stimulation (EC50) was 4.68 x 10(-5) M. This effect was inhibited by indomethacin and was related to a sodium transport, since the H2O2-induced increase in Isc could be prevented or abolished by 1) apical addition of benzamil (10(-6)M) and 2) substitution of sodium with N-methyl-glucamine. H2O2 exposure also induced indomethacin-sensitive increase in released prostaglandin (PG) E2 (EC50 = 5.62 x 10(-5) M) and in cAMP content (EC50 = 3.95 x 10(-5) M) with similar kinetics. These results suggest that exposure of MESV cells to oxidants stimulates the production of PGE2, which in turn increases the transepithelial sodium transport rate.

Stimulation of sodium transport by oxidants in middle ear epithelium in primary culture

Primary cultures of middle ear (ME) epithelial cells from gerbils were used to investigate the effect on ion transport of reactive oxygen species (ROS), which are major inflammatory mediators. Short-circuit current measurements revealed an unexpected result: low concentrations of ROS induced an increase in transepithelial sodium transport. This stimulation was mediated by the endogenous synthesis of prostaglandin E2, which in turn increased the intracellular adenosine 3',5'-cyclic monophosphate (cAMP) content. This effect was blunted by indomethacin. By stimulating sodium and fluid transport, ROS may reduce the depth of the periciliary fluid layer, and may thus be involved in the impairment of mucociliary clearance which initiates chronic otitis media.

Parathyroid hormone stimulates ecto-5'-nucleotidase activity in renal epithelial cells: role of protein kinase-C

PTH-induced phosphaturia is exerted in part by cAMP added to the renal tubular lumen under the influence of the hormone. Modulation of renal phosphate transport by luminal cAMP requires degradation of the nucleotide into adenosine by brush-border membrane ectoenzymes, among them ecto-5'-nucleotidase (5'-NU). Hormonal modulation of 5'-NU activity was evaluated in cultured opossum kidney cells. PTH (1-100 nM) stimulated 5'-NU in a time-, concentration-, and protein synthesis-dependent manner. The effect of PTH-(1-34) was mimicked by PTH-(3-34), which does not activates adenylate cyclase, and by phorbol 12-myristate 13-acetate (PMA), but not by forskolin or (Bu)2cAMP. Down-regulation or pharmacological inhibition of protein kinase-C (PKC) abolished the effect of PTH fragments and PMA. PTH fragments increased intracellular Ca2+ and translocated PKC activity to the membrane. PTH or PMA did not affect 5'-NU messenger RNA content. Inhibition of sodium-phosphate cotransport by extracellular cAMP was decreased by 5'-NU inhibition and was magnified by PTH. These results indicate that 1) PTH stimulates 5'-NU activity in renal proximal tubular cells in a manner involving PKC activation and de novo protein synthesis; and 2) this effect participates in PTH modulation of renal phosphate transport.

[Unusual twin pregnancy: one in the pseudo-unicornate uterus and the other in the rudimentary uterine horn. Discussion on the diagnosis and management during pregnancy]

An unusual twin pregnancy was diagnosed echographically at 18 weeks gestation and confirmed by magnetic resonance imaging. One foetus was in a pseudo unicornis uterus and the other in a rudimentary uterus cornu. The risk in such cases, as also reported in the literature, is rupture of the rudimentary cornu at about 20 weeks gestation. In this case the patient was carefully monitored to 23 weeks when the pregnancy in the rudimentary cornu stopped spontaneously. The foetus in the pseudounicornis developed normally to 38 week term. This exceptional observation emphasizes the risk of pregnancy in a blind uterus cornu.

In vitro electrogenic K secretion in the frog semicircular canal: absence of effect of streptomycin

In vitro, the frog semicircular canal secretes an endolymph-like fluid, i.e. a K-rich, positively polarized fluid. This electrogenic K secretion involved basolateral Na+, K(+)-ATPase and Na-K-Cl co-transporter and a luminal protein possessing sulfhydryl groups blocked by N-ethylmaleimide. Streptomycin, an ototoxic antibiotic, is known to block the non-specific mechano-dependent channels in the sensory cells of the ampulla of the semicircular canal. The aim of the present study was to investigate the possible effect of streptomycin on the K fluxes in the ampulla of the semicircular canal. The posterior frog semicircular canal was isolated and the lumen was filled with perilymph-like solution containing or not containing 0.5 mM streptomycin. The luminal K concentration and the transepithelial potential were measured and the unidirectional K fluxes calculated. The K influxes (into the lumen, pmoles/min/mm2) were 114 +/- 25.9 and 111 +/- 3.2 (mean +/- SE, n = 3) in the absence and presence of streptomycin, respectively. The transepithelial potential was not altered (4.0 +/- 1.08 mV versus 3.4 +/- 1.03 mV, n = 3). When ouabain (10(-3)M) was added to the basolateral solution together with luminal streptomycin, no further alteration occurred as compared with the effect of ouabain alone. These results suggest that in these conditions, the sensory organ does not have a major role in the endolymphatic K secretion in the ampulla of the frog semicircular canal.

Extracerebral toxoplasmosis in patients infected with HIV. A French National Survey

A French nationwide survey of extracerebral toxoplasmosis (ECT) in HIV-infected patients was performed between January 1990 and September 1992. All French hospitals were surveyed, and all but a few responded. Data collected included epidemiologic, clinical, and biologic features; therapy; and outcome. During the 33-month survey, 199 cases were collected. The prevalence of ECT in patients with AIDS can be estimated at 1.5%-2%. Age, sex, and HIV risk factors were similar to those of the general AIDS population in France. Extracerebral toxoplasmosis appeared mainly in HIV-infected patients with advanced immunosuppression: the mean CD4+ lymphocyte count was 57/mm3(+/- 99). The localizations observed were: eyes (50% of patients); lung (26%); disseminated (at least 2 extracerebral visceral localizations) (11.5%); peripheral blood (acute febrile syndrome with isolated positive parasitemia) (3%); heart (3%); bone marrow (3%); bladder (1%); and isolated cases of rhinopharynx, skin, liver, lymph nodes, conus medullaris, and pericardium. In this survey, muscular and pancreatic localizations were always associated with other extracerebral localizations. A cerebral localization was diagnosed in 41% of cases. Serologic data provided little information. Ocular fundus examination, bronchoalveolar lavage, tissue biopsy, and search for parasitemia were the main diagnostic procedures. Treatment was the same as for cerebral toxoplasmosis. A clinical response was observed in 64% of cases; 19% relapsed. Death occurred in 106 (53%) cases and was related to ECT in 34% of cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Antidiuretic hormone restores the endolymphatic longitudinal K+ gradient in the Brattleboro rat cochlea

In the cochlea, endolymph is hyperosmotic to plasma and perilymph. To test the hypothesis that antidiuretic hormone is involved in the modulation of endolymph secretion, the electrochemical composition of cochlear fluids, endolymph and perilymph, was studied in three groups of anaesthetized rats: control Long Evans rats, homozygous Brattleboro rats that are genetically deprived of antidiuretic hormone, and Brattleboro rats that were treated with antidiuretic hormone (dDAVP, 0.5 microgram/100 g body weight/24 h during 8 days). Endolymph was sampled from the scala media at each turn of the cochlea and perilymph from the scala vestibuli. In Long Evans rats, the endocochlear potential, the endolymphatic K+ and Cl- concentrations decreased from base to apex of the cochlea as previously reported in guinea pigs and Sprague Dawley rats. In Brattleboro rats, the endocochlear potential and the Cl- concentration gradients were still present, whereas the K+ concentration gradient were still present, whereas the K+ concentration gradient was absent. This K+ gradient was restored by the administration of dDAVP, which increased the K+ concentration at the base of the cochlea. This work indicates that the K+ secretion in endolymph, and thus the osmolality, may be locally modulated by the antidiuretic hormone, probably via V2 receptors.

Multiple modulation of Na-dependent Pi uptake by cellular Ca in MDCK cells

The events accounting for the adaptation of the sodium-dependent phosphate cotransport (Na-Pi) to phosphate deprivation other than genomic regulation remain unknown. The involvement of changes in intracellular calcium concentration was investigated in Madin-Darby canine kidney (MDCK) cells. Calcium concentration was decreased by 15 h of phosphate deprivation (-24 to -35%) or low-calcium medium (calcium deprivation) (-45%), or 8-(N,N'-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB8) (-32%). Calcium deprivation stimulated Na-Pi (2-fold at 1 h and up to 15 h) by increasing the affinity for phosphate. Combined calcium and phosphate deprivation had more than additive effects on phosphate uptake. The effect of a 15-h calcium deprivation, but not of a 2-h one, was dependent on gene transcription and protein synthesis. TMB8 stimulated phosphate uptake similarly to phosphate deprivation (increase in maximum velocity dependent on gene transcription). The ionophore A23187 decreased basal Na-Pi as well as its stimulation by phosphate or calcium deprivation or by TMB8. Calcium deprivation stimulated (3.2-fold increase) the sodium-coupled alanine transport, whereas phosphate deprivation and TMB8 did not. We conclude that 1) phosphate deprivation decreases intracellular calcium concentration, 2) low intracellular calcium concentration is instrumental in the stimulation by prolonged calcium or phosphate deprivation of Na-Pi, and 3) phosphate or calcium deprivation modulates Na-Pi through different cellular pathways.

Is the endolymphatic K secretion electrogenic?

The endolymphatic potential is assumed to result from active K transport into the endolymphatic compartment and passive K diffusion in the opposite direction. However, in several in vivo experiments, changes in the endolymphatic potential differed from those in the endolymphatic K concentration. Moreover, in in vitro experiments, a negative endolymphatic potential was observed in the presence of ouabain without K gradient between the two compartments. These observations suggest that the coupling between the K transport and the genesis of the endolymphatic potential is not tight. Several factors may separately influence the endolymphatic potential and the K transport such as the acid-base equilibrium, the integrity of Reissner's membrane, the hormonal status, and the Na transport.

Post-transfusional anti-HCV-negative, non-A, non-B hepatitis. (I) a prospective clinical and epidemiological survey

Despite the identification of hepatitis C virus (HCV) and the detection of anti-HCV antibodies in the serum of infected individuals, a sizeable proportion of patients who develop transfusion-associated acute non-A, non-B hepatitis following surgery do not develop anti-HCV antibodies. The cause of this disease remains unknown. To assess the role of homologous blood transfusion in anti-HCV-positive and -negative, non-A, non-B hepatitis following surgery, patients receiving homologous blood, autologous blood alone, or no transfusions were prospectively studied. Consumption of potentially hepatotoxic drugs was also quantified. Anti-HCV antibodies were tested retrospectively when commercial assays became available. Of the 181 patients who received homologous blood which tested negative for surrogate markers of infectivity, 19 (10.5%) developed non-A, non-B hepatitis, associated with anti-HCV seroconversion in three cases. Of the 90 autologous blood recipients, non-A, non-B hepatitis developed in one (1.1%), who did not seroconvert to anti-HCV. Of the 64 untransfused patients, non-A, non-B hepatitis developed in one (1.6%), who was anti-HCV-positive before surgery. Logistic regression analysis showed that the occurrence of non-A, non-B hepatitis was associated with homologous blood transfusion, but not with the consumption of potentially hepatotoxic drugs. The 16 homologous-blood recipients who developed anti-HCV-negative, non-A, non-B hepatitis had received blood from 70 donors, none of whom had detectable anti-HCV antibodies but six of whom had minimal elevations of serum aminotransferase activity. Anti-HCV-negative, non-A, non-B hepatitis is mainly transfusion-transmitted in the surgical setting. Known hepatotropic agents may be involved despite the absence of usual serum markers, but our results are also consistent with the involvement of an unidentified non-A, non-B, non-C agent.

Middle ear cell line that maintains vectorial electrolyte transport

The middle ear epithelium plays a major role in keeping the temporal bone cavities fluid-free and air-filled, which is a mandatory condition to allow optimum transmission of the sound vibrations from the tympanic membrane to the inner ear. Previous works have recently established the absorptive function of the middle ear epithelium, using primary cultures derived from Mongolian gerbil (Meriones unguiculatus). Because of the paucity of cells as obtained by enzymatic digestion, we developed a middle ear cell line (MESV) using wild-type SV40 infection of primary culture of Mongolian gerbil's middle ear epithelial cells. Transformation was attested by nuclear expression of SV40 large T antigen, prolonged in vitro passages (presently beyond 50 passages), and tumor-inducing ability when subcutaneously injected in athymic mice. Transport properties were evaluated after the fifteenth passage. MESV cells retained most cardinal properties of the original middle ear epithelial cells: cell polarization was evidenced by the presence of mature junctional complexes that separate the cell membrane in two distinct domains, with apical microvilli at the luminal side, and by vectorial sodium transport responsible for the transepithelial lumen-negative potential difference (-9.3 +/- 0.14 mV in culture conditions (n = 9), -2.1 +/- 0.25 mV after overnight growth factors and serum deprivation). Short-circuit current was, like in primary cultures, mainly related to a sodium transport occurring through amiloride-sensitive apical sodium channels, since apical addition of amiloride (10(-5) M) reduced ISC from 7.0 +/- 1.4 to 0.6 +/- 0.1 microA/cm2 (P < 0.01, n = 6). Cellular cAMP content was increased by isoproterenol and prostaglandin E2 from 40.5 +/- 5.6 to 258.5 +/- 17.3 and 55.6 +/- 6.2 pmol/mg protein per 5 min, respectively (P < 0.05, n = 10). Isoproterenol and prostaglandin E2 increased ISC with very similar maximal effects: isoproterenol (10(-4) M) increased ISC from 5.73 +/- 0.31 to 12.77 +/- 0.39 microA/cm2, while prostaglandin E2 increased ISC from 5.47 +/- 0.21 to 12.87 +/- 0.42 (n = 3). Since amiloride (10(-5) M) abolished this stimulation, this may be related to an increase of the electrogenic sodium transepithelial transport. The MESV cell line could provide an interesting tool as a model of middle ear epithelial cells for the study of pathophysiological modulations of ion transport.

N-ethylmaleimide-inhibited electrogenic K+ secretion in the ampulla of the frog semicircular canal

1. The mechanisms of K+ secretion into endolymph were studied on a preparation of isolated semicircular canal with different pharmacological inhibitors. Three periods of 5 or 30 min were performed, the first as control, the second in the presence of the drugs added to the apical or the basolateral bathing solution, and the third as recovery. Apical fluid was sampled at the beginning and the end of each period, transepithelial potential was recorded, Na+, K+, and Cl- concentrations, and K+ efflux, with 86Rb+ as a tracer, were measured and K+ fluxes were calculated. 2. When both sides of the epithelium were bathed with perilymph-like solution, the epithelium absorbed Na+, secreted K+, and generated a lumen positive potential. 3. The ATPases inhibitors, ouabain (10(-5) and 10(-3) M) and N-ethylmaleimide (10(-4) and 10(-3) M) inhibited the electrogenic K+ secretion when added to the basolateral fluid. N-ethylmaleimide (10(-3) M) applied to the apical fluid during a 5 min period decreased the K+ influx by 43% and the transepithelial potential by 66%. Other ATPase inhibitors, harmaline (10(-3) M), omeprazole (10(-4) M), vanadate (10(-4) M and 10(-3) M), N,N'-dicyclohexylcarbodiimide (DCC, 10(-5) M), 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD-Cl, 5 x 10(-6) M and 5 x 10(-5) M), and bafilomycin (10(-7) M) did not affect the K+ transport nor the transepithelial potential when they were added to the apical fluid. 4. The Na(+)-K(+)-Cl- co-transporter inhibitor, bumetanide, decreased both the transepithelial potential and the K+ transport when added to the basolateral solution but not to the apical one. At 10(-6) M, bumetanide maximally decreased the K+ influx by about 60%. 5. K+ channel blockers, quinine (10(-4) M), TEA (5 x 10(-3) M), added to the apical solution and barium (2 x 10(-3) M) added to either the apical or the basolateral solutions, did not affect the K+ transport and the transepithelial potential. 6. The carbonic anhydrase inhibitor acetazolamide (10(-3) M) added to both apical and basolateral solutions did not affect the K+ transport and the transepithelial potential. 7. It is concluded that, in the ampulla of the semicircular canal, a basolateral Na(+)-K(+)-Cl- co-transporter energized by the Na+, K(+)-ATPase was involved for 60% in the K+ secretion into endolymph. The electrogenic K+ transport would partly depend on a N-ethylmaleimide-sensitive protein possibly located at the apical plasma membrane or intracellularly.

Hypertrophic pulmonary osteoarthropathy associated with granulomatous Pneumocystis carinii pneumonia in AIDS

A case of hypertrophic pulmonary osteoarthropathy (HPOA) in a HIV-infected patient with granulomatous Pneumocystis carinii pneumonia is described. This is the third case of HPOA associated with AIDS reported in the literature. Granulomatous P. carinii pneumonia is an unusual manifestation of P. carinii infection. Surgical treatment of this condition may lead to the dramatic spread of P. carinii causing a fulminant course with fatal outcome.

Modulation of Na-H exchange activity by angiotensin II in opossum kidney cells

Angiotensin II (ANG II) was shown to modulate transport in the renal proximal tubule through both inhibition of adenylate cyclase and protein kinase C (PKC) activation. We evaluated the effects of ANG II on adenosine 3',5'-cyclic monophosphate (cAMP) content and Na-H exchange activity (amiloride-sensitive Na influx) in two strains of opossum kidney (OK) cells originating from different sources, OK-VD and OK-RR cells. In OK-VD cells, ANG II inhibited basal and parathyroid hormone (PTH)-induced cAMP generation in a pertussis toxin-sensitive manner and reversed PTH inhibition of Na-H exchange. These effects of ANG II were prevented by PD 123319, a selective nonpeptide antagonist of AT2 receptors. In contrast, DuP 753, which antagonizes selectively AT1 receptors, had no effect. In OK-RR cells, ANG II had no effect on cAMP content and decreased Na-H exchange activity. The effect of ANG II persisted in the presence of PTH but was abolished by PKC downregulation and by DuP 753, but not by PD 123319. In conclusion, two types of ANG II receptors, coupled to distinct signaling pathways, were expressed independently in OK cells originating from two different sources and mediated opposite effects of ANG II on Na-H exchange activity. Those models provide a powerful tool for studying the intracellular steps involved in the tubular effects of ANG II and to evaluate the effect of pharmacological inhibitors of ANG II binding to its receptors.

Mechanisms whereby extracellular adenosine 3',5'-monophosphate inhibits phosphate transport in cultured opossum kidney cells and in rat kidney. Physiological implication

The mechanism of phosphaturia induced by cAMP infusion and the physiological role of extracellular cAMP in modulation of renal phosphate transport were examined. In cultured opossum kidney cells, extracellular cAMP (10-1,000 microM) inhibited Na-dependent phosphate uptake in a time- and concentration-dependent manner. The effect of cAMP was reproduced by ATP, AMP, and adenosine, and was blunted by phosphodiesterase inhibitors or by dipyridamole which inhibits adenosine uptake. [3H]cAMP was degraded extracellularly into AMP and adenosine, and radioactivity accumulated in the cells as labeled adenosine and, subsequently, as adenine nucleotides including cAMP. Radioactivity accumulation was decreased by dipyridamole and by inhibitors of phosphodiesterases and ecto-5'-nucleotidase, assessing the existence of stepwise hydrolysis of extracellular cAMP and intracellular processing of taken up adenosine. In vivo, dipyridamole abolished the phosphaturia induced by exogenous cAMP infusion in acutely parathyroidectomized (APTX) rats, decreased phosphate excretion in intact rats, and blunted phosphaturia induced by PTH infusion in APTX rats. These results indicate that luminal degradation of cAMP into adenosine, followed by cellular uptake of the nucleoside by tubular cells, is a key event which accounts for the phosphaturic effect of exogenous cAMP and for the part of the phosphaturic effect of PTH which is mediated by cAMP added to the tubular lumen under the influence of the hormone.