The concentration-dependence of CRF-like diuretic peptide: mechanisms of action.

1998 ◽  
Vol 201 (11) ◽  
pp. 1753-1762 ◽  
Author(s):  
T M Clark ◽  
T K Hayes ◽  
G M Holman ◽  
K W Beyenbach
Keyword(s):  
Short Circuit ◽  
Second Messenger ◽  
Short Circuit Current ◽  
Paracellular Pathway ◽  
Ionophore A23187 ◽  
Na Transport ◽  
Principal Mechanism ◽  
Cl Transport ◽  
Mediated Effects ◽  
Stimulation Of

The mechanism of action of synthetic CCRF-DP, the corticotropin-releasing factor (CRF)-related diuretic peptide of the salt marsh mosquito Culex salinarius, was investigated in isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti. A low concentration of CCRF-DP (10(-9)mol l-1) caused a small but insignificant increase in transepithelial secretion of NaCl and fluid, but significantly reduced transepithelial voltage and resistance without a change in short-circuit current, pointing to the stimulation of passive Cl- transport through the paracellular pathway as the principal mechanism of a mild diuresis. Significant changes in voltage and resistance but not in short-circuit current were duplicated by the ionophore A23187 (0.4 micromol l-1), suggesting Ca2+ as a second messenger at 10(-9)mol l-1 CCRF-DP. A high concentration of CCRF-DP (10(-7)mol l-1) significantly increased transepithelial secretion of NaCl and fluid and significantly increased short-circuit current, pointing to the stimulation of active Na+ transport through the transcellular pathway as the mechanism of a strong diuresis. This effect was mimicked by dibutyryl-cAMP, suggesting cAMP as a second messenger at 10(-7)mol l-1 CCRF-DP. Dibutyryl-cGMP had no effects. These results suggest dose-dependent, receptor-mediated effects of CCRF-DP that target discrete transport pathways via discrete second messengers: low concentrations of CCRF-DP cause a mild diuresis, apparently via Ca2+-mediated effects on paracellular Cl- transport, and high concentrations cause a strong diuresis via cAMP-mediated effects on active transcellular Na+ transport in addition to the effects on the paracellular pathway.

Metabolic requirements for anaerobic active Cl and Na transport in the bullfrog cornea

1979 ◽  
Vol 236 (5) ◽  
pp. C268-C276 ◽  
Author(s):  
P. S. Reinach ◽  
H. F. Schoen ◽  
O. A. Candia
Keyword(s):  
Energy Source ◽  
Amphotericin B ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Anaerobic Glycolysis ◽  
Anaerobic Conditions ◽  
Na Transport ◽  
Sufficient Energy ◽  
Aerobic And Anaerobic ◽  
Stimulation Of

In the bullfrog cornea, the relationships between the rates of aerobic and anaerobic glycolysis and active Cl and Na transport were studied. In NaCl Ringer (glucose-free), the short-circuit current (SCC) declined much more slowly under aerobic than under anaerobic conditions. The aerobic lactate effluxes in glucose-free and glucose-rich NaCl Ringer were 0.08 and 0.23 micromol/h.cm2, respectively. The transition to anoxia caused these values to increase significantly and was accompanied by depletion of endogenous glycogen in glucose-free Ringer. In Na2SO4 Ringer, amphotericin B (10(-5) M) stimulation of the aerobic SCC was not dependent on the presence of glucose but under anoxia, SCC stimulation required glucose. In Na2SO4 (glucose-rich) Ringer, amphotericin B stimulated the aerobic lactate efflux from 0.26 to 0.36 mumol/h.cm2 and anoxia increased it to 0.55 micromol/h.cm2. In NaCl Ringer, the addition of either 0.5 mM adenosine or 1 mM ATP with 26 mM glucose restored the anaerobic-inhibited SCC and lactate efflux of glucose-depleted corneas. The results show that the reactions of glycolysis are a sufficient energy source for supporting active Na and Cl transport.

Chronic regulation of transepithelial Na+ transport by the rate of apical Na+ entry

1996 ◽  
Vol 270 (2) ◽  
pp. C600-C607 ◽  
Author(s):  
M. D. Rokaw ◽  
E. Sarac ◽  
E. Lechman ◽  
M. West ◽  
J. Angeski ◽  
...  
Keyword(s):  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Maximal Activity ◽  
Na Channels ◽  
Na Transport ◽  
Bottom Structures ◽  
Stimulation Of

In several settings in vivo, prolonged inhibition of apical Na+ entry reduces and prolonged stimulation of apical entry enhances the ability of renal epithelial cells to reabsorb Na+, an important feature of the load-dependent regulation of renal tubular Na+ transport. To model this load dependency, apical Na+ entry was inhibited or stimulated for 18 h in A6 cells and vectorial transport was measured as short-circuit current (Isc) across monolayers on filter-bottom structures. Basal amiloride-sensitive Isc represents the activity of apical Na+ channels, whereas Isc after permeabilization of the apical membrane to cations with nystatin represents maximal activity of the basolateral Na(+)-K(+)-ATPase. Chronic inhibition of apical Na+ entry by 18-h apical exposure to amiloride or replacement of apical Na+ with tetramethylammonium (TMA+), followed by washing and restoration of normal apical medium, revealed a persistent decrease in Isc that remained despite exposure to nystatin. Both basal and nystatin-stimulated Isc recovered progressively after restoration of normal apical medium. In contrast, chronic stimulation of apical Na+ entry by short circuiting the epithelium increased Isc in the absence and presence of nystatin, indicating upregulation of both apical Na+ channels and basolateral Na(+)-K(+)-ATPase. Basolateral equilibrium [3H]ouabain binding was reduced to 67 +/- 5% in TMA+ vs. control cells, whereas values in 18-h short-circuited cells increased by 42 +/- 19%. The results demonstrate that load dependency of tubular Na+ transport can be modeled in vitro and indicate that the regulation of Na(+)-K(+)-ATPase observed in these studies occurs in part by changes in the density of functional transporter proteins within the basolateral membrane.

Modification of carboxyl of Na+ channel inhibits aldosterone action on Na+ transport

1983 ◽  
Vol 245 (6) ◽  
pp. F726-F734 ◽  
Author(s):  
J. Kipnowski ◽  
C. S. Park ◽  
D. D. Fanestil
Keyword(s):  
Amphotericin B ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Na Channel ◽  
Dependent Manner ◽  
Na Channels ◽  
Na Transport ◽  
Maximal Increase ◽  
Osmotic Water ◽  
Stimulation Of

We investigated the effect of the carboxyl-selective reagent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on aldosterone stimulation of Na+ transport in the urinary bladder of the toad. Na+ transport, measured as the short-circuit current (SCC), was irreversibly inhibited by EEDQ in a dose- and time-dependent manner prior to addition of aldosterone. The greater the percentage inhibition by EEDQ (X), the smaller was the maximal increase of SCC after aldosterone (Y). This relationship gave the regression equation Y = 128.41 - 1.73X, r = -0.99 (n = 35). Evidence that the inhibition of SCC produced by EEDQ was limited to effects at the mucosal membrane was attested by the following: 1) EEDQ did not alter the stimulation by aldosterone of the osmotic water flow response to antidiuretic hormone; 2) whereas inhibition of protein synthesis by cycloheximide prevented this effect of aldosterone; 3) amphotericin B fully restored SCC previously inhibited by EEDQ to the level produced in tissues not inhibited by EEDQ; 4) comparison of the effects of amiloride vs. EEDQ pretreatment on the SCC response to aldosterone and amphotericin B revealed nearly identical characteristics; 5) in contrast, amphotericin B stimulation of SCC was limited when Na+ transport was limited by antimycin A (an inhibitor of energy production) or by ouabain. The findings fail to provide positive evidence for the hypothesis that aldosterone induces the synthesis of new Na+ channels but are consistent with hormonal activation of previously existing but nonfunctioning Na+ channels.

Effect of brefeldin A on ADH-induced transport responses of toad bladder

1994 ◽  
Vol 266 (4) ◽  
pp. C1069-C1076 ◽  
Author(s):  
K. Weng ◽  
J. B. Wade
Keyword(s):  
Water Permeability ◽  
Short Circuit ◽  
Brefeldin A ◽  
Membrane Traffic ◽  
Short Circuit Current ◽  
Toad Urinary Bladder ◽  
Membrane Biogenesis ◽  
Na Transport ◽  
Stimulation Of

We have used brefeldin A (BFA) to examine the role of membrane traffic in the short-circuit current (ISC) and water permeability responses of the toad urinary bladder. BFA treatment of 1 or 5 micrograms/ml had a complex effect on the response of the ISC to antidiuretic hormone (ADH) or forskolin stimulation. Although the responses to initial challenges by ADH were not impaired by BFA, subsequent ISC responses were progressively reduced. Similarly, while the response to an initial challenge by forskolin was modestly reduced by BFA, subsequent responses were markedly reduced. Inhibition of protein synthesis with cycloheximide (CHM) affected ISC responses similarly. Neither BFA nor CHM had an effect on water permeability responses. These observations show that although the membrane traffic responsible for the water permeability response is insensitive to inhibition by BFA or CHM, the stimulation of Na+ transport becomes increasingly sensitive to these inhibitors with successive challenges by ADH or forskolin. Although initial increases in Na+ transport utilize preexisting components, subsequent responses appear to require an intact system for membrane biogenesis.

Regulation of electrogenic Na+ transport across leech skin

1995 ◽  
Vol 268 (3) ◽  
pp. R605-R613 ◽  
Author(s):  
W. M. Weber ◽  
U. Blank ◽  
W. Clauss
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Na Channel ◽  
Monovalent Cations ◽  
Serosal Side ◽  
Na Transport ◽  
Permeability Ratio ◽  
Cyclic Monophosphate ◽  
Apical Side ◽  
Stimulation Of

The dorsal integument of the medical leech Hirudo medicinalis exhibits a marked amiloride-sensitive Na+ absorption. With 20 mM Na+ in the apical solution, the transepithelial short-circuit current (Isc) was approximately 40% higher than with 115 mM Na+, whereas the transepithelial potential (VT) with 20 mM Na+ was -35.7 +/- 4.5 and -20.6 +/- 2.6 mV with 115 mM Na+. Amiloride (100 microM) inhibition at 20 mM apical Na+ was also significantly larger than with 115 mM Na+ in the solution. Benzamil (100 microM) showed additional inhibition after amiloride. Large transient overshooting currents occurred only when 115 mM Na+ was added after some minutes of Na(+)-free apical solution. Addition of adenosine 3',5'-cyclic monophosphate (cAMP) to the serosal side in the presence of 115 mM apical Na+ nearly doubled Isc. This cAMP effect was reduced to only 20% in the presence of 20 mM Na+. Guanosine 3',5'-cyclic monophosphate (cGMP) slightly increased Isc, whereas ATP showed biphasic potency. Removal of calcium from the apical side resulted in a large stimulation of amiloride-sensitive Isc only in the presence of 115 mM Na+. When currents were activated with cAMP, a deprivation of Ca2+ modestly reduced the amiloride-sensitive Isc. The Na+ channel of leech integument was found highly selective for Na+ over other monovalent cations. The permeability ratio for Na+ over K+ was approximately 30:1; the selectivity relationship for the investigated cations was Na+ > Li+ > NH4+ > K+ approximately Cs+ approximately Rb+.

Forskolin effects on frog and rabbit corneal epithelium ion transport

1986 ◽  
Vol 251 (3) ◽  
pp. C448-C454 ◽  
Author(s):  
O. A. Candia ◽  
L. R. Grillone ◽  
T. C. Chu
Keyword(s):  
Corneal Epithelium ◽  
Rana Catesbeiana ◽  
Apical Membrane ◽  
Short Circuit ◽  
Control Level ◽  
Short Circuit Current ◽  
Potential Difference ◽  
Ionophore A23187 ◽  
Intracellular Recordings ◽  
Stimulation Of

The effects of forskolin on the electrophysiological parameters of the isolated corneal epithelium from bullfrog (Rana catesbeiana) were investigated. Forskolin stimulated the short-circuit current (SCC) and transepithelial potential difference (PDt), while reducing the transepithelial resistance. These effects were absent in Cl- -free bathing solutions. Furosemide, added either before or after forskolin, completely blocked the effects. Epinephrine and A23187, added after forskolin, produced only a small additional stimulation of the SCC. Propranolol neither blocked nor reduced the effect of forskolin. Forskolin increased the stroma to tear 36Cl flux by 61% and the tear to stroma 36Cl flux by 64%. Intracellular recordings showed that forskolin depolarized the potential difference across the apical membrane and reduced the apical/basolateral resistance ratio. Intracellular recordings in the isolated rabbit epithelium showed the same effects by forskolin except that there was only a brief stimulation of PDt, after which it stabilized slightly below the control level. These results are consistent with an increase in apical membrane permeability similar to that produced by adenosine 3',5'-cyclic monophosphate, epinephrine, and the Ca2+ ionophore A23187.

Suppression of coupled Na-Cl absorption by aldosterone and dexamethasone in rat distal colon in vitro

1984 ◽  
Vol 246 (6) ◽  
pp. F785-F793 ◽  
Author(s):  
R. D. Perrone ◽  
S. L. Jenks
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Rat Colon ◽  
Na Transport ◽  
Unidirectional Flux ◽  
Rat Distal Colon ◽  
Marked Suppression ◽  
Stimulation Of

Basal Na absorption in the rat colon is coupled to that of Cl in an electroneutral fashion. We previously determined that aldosterone or dexamethasone induces amiloride-sensitive mucosal-to-serosal Na flux approximately equal to the amiloride-sensitive short-circuit current in rat distal colon in vitro. However, the effect of these steroids on coupled Na-Cl absorption was not examined. For this purpose, we determined the unidirectional flux of Na and Cl in voltage-clamped distal colon segments from rats treated with aldosterone or dexamethasone. Amiloride was used as a probe for conductive Na absorption, and acetazolamide and Cl-free solutions were used as probes for coupled Na-Cl absorption. Our results indicate that the nature of colonic Na absorption is markedly changed after treatment with these steroids. In contrast to findings in the untreated rat, colonic Na absorption after treatment with aldosterone or dexamethasone was largely independent of the presence of Cl. Net Cl absorption and acetazolamide sensitivity were both greatly diminished. Thus, aldosterone and dexamethasone have multiple effects on Na transport in rat distal colon. In addition to the stimulation of conductive Na absorption by aldosterone, an effect well described in other epithelia, there is marked suppression of coupled Na-Cl absorption. Dexamethasone was less effective in suppressing Cl absorption but equally effective in stimulating conductive Na absorption. These steroid effects were greater in the terminal 1-2 cm of the rat colon.

Interaction between sodium and chloride transport in canine tracheal mucosa

1979 ◽  
Vol 46 (1) ◽  
pp. 111-119 ◽  
Author(s):  
F. J. Al-Bazzaz ◽  
Q. Al-Awqati
Keyword(s):  
Hormonal Regulation ◽  
Chloride Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Na Transport ◽  
Tracheal Mucosa ◽  
Electrically Conductive ◽  
Ussing Chambers ◽  
Cl Secretion ◽  
Cl Transport

Canine tracheal mucosae were dissected and mounted as flat sheets in Ussing chambers. Unidirectional isotope fluxes of 22Na and 36Cl were performed across paired mucosae from the same animal. The average spontaneous potential difference was 42 + 1.2 mV (mean +/- SE) lumen negative. The short-circuit current (SCC) 3.09 +/- 0.36 mueq/cm2.h was accounted for by a net Cl secretion of 2.46 +/- 0.26 mueq/cm2.h toward the mucosa and net Na absorption of 0.46 +/- 0.13 mueq/cm2.h toward submucosa. Removal of Cl depressed SCC but had no effect on unidirectional or net Na transport (n = 7). By contrast, removal of Na (n = 6) or the addition of ouabain (n = 7) abolished net Cl secretion and greatly reduced SCC. Theophylline (n = 6) added to the submucosal bath no significant effect on Na transport but stimulated SCC and Cl secretion, suggesting hormonal regulation of Cl transport. The results suggest that the active transport of Na and Cl in this epithelium occur by electrically conductive pathways, i.e., the transport is “electrogenic.” Further it appears that Na transport is independent of the presence of Cl but that Cl transport depends on some parameter of active Na transport.

Active transport and exchange diffusion of Cl across the isolated skin of Rana pipiens

1985 ◽  
Vol 249 (3) ◽  
pp. F424-F431 ◽  
Author(s):  
K. Drewnowska ◽  
T. U. Biber
Keyword(s):  
Rana Pipiens ◽  
Recent Observation ◽  
Short Circuit ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Na Transport ◽  
Exchange System ◽  
Exchange Diffusion ◽  
Cl Transport ◽  
Apical Side

Transepithelial Cl influx and efflux were measured in pairs of frog skin (Rana pipiens) matched according to short-circuit current, tissue conductance, and transepithelial potential (TEP). The skins were bathed symmetrically in NaCl Ringer and voltage clamped at TEP values ranging from -60 to +60 mV. At 0 TEP, Cl influx and net inward Cl movement (in neq X h-1 X cm-2) were, respectively, 961 +/- 116 and 463 +/- 68 in NaCl Ringer, 509 +/- 52 and 202 +/- 53 in amiloride-treated skins, 4,168 +/- 777 and 1,444 +/- 447 in theophylline-treated skins, and 587 +/- 38 and 97 +/- 44 in Na-free Ringer. A correlation was discovered between short-circuit current and Cl fluxes corresponding to a 2:6:1 relationship between changes in active Na transport and active Cl transport. Deviations from the predicted Cl flux ratio indicate the presence of exchange diffusion in the range of spontaneously occurring TEPs, in contrast to observations on R. temporaria and R. esculenta. The experiments indicate that a substantial portion of transepithelial Cl movement proceeds transcellularly 1) via active Cl transport that is Na dependent, amiloride sensitive, stimulated by theophylline, and apparently correlated with active Na transport, and 2) by means of exchange diffusion that not only occurs under short-circuit conditions but also at positive TEPs. It is possible to explain both the exchange diffusion and the properties of active Cl transport by a Cl-HCO3 exchange system at the apical side of the transporting cell that interacts with a Na-H exchange mechanism, a notion consistent with the recent observation of an amiloride-induced decrease in intracellular pH.

[15N]- and [14C]glutamine fluxes across rabbit ileum in experimental bacterial diarrhea

1992 ◽  
Vol 262 (2) ◽  
pp. G312-G318 ◽  
Author(s):  
S. K. Nath ◽  
P. Dechelotte ◽  
D. Darmaun ◽  
M. Gotteland ◽  
M. Rongier ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Rabbit Ileum ◽  
Diarrheagenic Escherichia Coli ◽  
Nacl Absorption ◽  
Cl Transport ◽  
Stimulation Of ◽  
Bacterial Diarrhea

L-Glutamine (Gln) fluxes and the effects of Gln on Na and Cl transport were studied across the ileum of healthy and rabbit diarrheagenic Escherichia coli (RDEC-1)-infected weanling rabbits. Stable ([alpha-15N]Gln) and radioisotopic ([U-14C]Gln) tracers provided identical estimates of Gln transport both in healthy (H) and infected (I) rabbits. RDEC-1 infection, however, decreased net Gln flux [Jnet[14C]Gln = 682 +/- 147 (H) vs. 278 +/- 63 (I); Jnet[15N]Gln = 739 +/- 160 vs. 225 +/- 110 nmol.h-1.cm-2] due to a reduction in mucosal-to-serosal flux. After addition of Gln, increases in net Na absorption [delta Jnet[15N]Gln = 1.87 +/- 0.45 (H) vs. 0.70 +/- 0.27 (I) microeq.h-1.cm-2] and short-circuit current (delta Isc) [1.80 +/- 0.40 (H) vs. 0.74 +/- 0.14 (I) microeq.h-1.cm-2] were also reduced in infected rabbits. Addition of glucose after Gln, however, stimulated Na absorption further. These results indicate that 1) Gln is actively absorbed as intact Gln molecule across rabbit ileum; 2) Gln stimulates an electrogenic Na absorption in a 1:2 ratio that may be further stimulated by glucose; and 3) in RDEC-1 infection electroneutral NaCl absorption, intact Gln absorption, and electrogenic stimulation of Na absorption by glutamine are reduced.

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