Urea and Na+ permeabilities in toad urinary bladder: one or two solute pathways?

It has been reported that toad urinary bladder amiloride not only reversibly blocks Na+ transport, but it also reversibly inhibits urea permeability (Pu). This finding prompted some queries: 1) Does Na+ transport rates and/or the cytosolic Na+ pool regulate Pu? 2) Does amiloride inhibit two different solute pathways or one pathway through which both Na+ and urea permeate? The following results were obtained in toad bladder. 1) The absence of mucosal Na+ does not interfere with basal or ADH-induced Pu. 2) Amiloride inhibits Pu in the absence of apical Na+. 3) The concentration of amiloride that produces half-maximal inhibition (K1/2) of the ADH-induced Na+ transport is 7 X 10(-7)M with 110 mM mucosal Na+, 7 X 10(-8)M with 1 mM apical Na+, and 2 X 10(-6)M in the absence of mucosal Ca2+; K1/2 of ADH-stimulated Pu is 9 X 10(-5)M and is not altered by lowering the mucosal Na+ concentration to 1 mM or deleting apical Ca2+. 4) Mucosal La3+ (10(-3)M): i) reversibly increases Na+ transport by 75%, potentiating the natriferic effect of ADH by 51%; ii) does not affect basal Pu and irreversibly blunts the ADH-mediated increase in Pu by 72%; and iii) has no effect on basal or ADH-induced osmotic flow. Identical results were obtained with Tm3+. These results suggest that the inhibitory effect of amiloride on amide permeation is not mediated by its effect on Na+ transport. There are three separate operational pathways for water, Na+, and urea; amiloride reversibly blocks those through which Na+ and urea permeate.(ABSTRACT TRUNCATED AT 250 WORDS)

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Effect of verapamil on the hydroosmotic response to antidiuretic hormone in toad urinary bladder

AJP Renal Physiology ◽

10.1152/ajprenal.1980.239.3.f250 ◽

1980 ◽

Vol 239 (3) ◽

pp. F250-F257 ◽

Cited By ~ 1

Author(s):

H. D. Humes ◽

C. F. Simmons ◽

B. M. Brenner

Keyword(s):

Urinary Bladder ◽

Antidiuretic Hormone ◽

Water Flow ◽

Calcium Ion ◽

Inhibitory Effect ◽

Coupling Factor ◽

Toad Bladder ◽

Toad Urinary Bladder ◽

Calcium Dependent

To investigate the role of the calcium ion in the hydroosmotic response to antidiuretic hormone (ADH), the effects of verapamil, an inhibitor of calcium ion entry into cells, on stimulated water flow was examined in vitro in the toad urinary bladder. Verapamil, 50 micro M, decreased ADH-stimulated osmotic water flow from 23.4 +/- 4.1 to 9.9 +/- 3.3 mg . min-1 . hemibladder-1 (mean +/- SE, n = 12, P < 0.001). That this inhibitory effect was due to a verapamil-induced alteration in cellular calcium metabolism is suggested by the findings that 45Ca2+ uptake by isolated toad bladder epithelial cells was reduced nearly 50% in the presence of verapamil and that reversibility of verapamil's inhibitory action was calcium dependent. Additionally, verapamil reduced theophylline- (20 mM) stimulated water flow from 22.8 +/- 2.7 to 9.5 +/- 2.9 mg . min-1 . hemibladder-1 (n = 7, P < 0.001) but enhanced cAMP- (10 mM) induced water flow from 12.8 +/- 2.5 to 21.6 +/- 1.1 ng . min-1 . hemibladder-1 (n = 7, P < 0.001). The latter effect was due, at least in part, to a direct inhibitory effect by verapamil on phosphodiesterase activity of toad bladder homogenates. These results, therefore, suggest that the calcium ion is an important coupling factor at the level of the adenylate cyclase enzyme complex for the stimulus-reabsorption coupling between ADH and the transporting epithelia of the toad urinary bladder.

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OSMOTIC INHIBITION OF THE NATRIFERIC RESPONSE OF THE TOAD URINARY BLADDER TO VASOPRESSIN

Journal of Endocrinology ◽

10.1677/joe.0.0670119 ◽

1975 ◽

Vol 67 (1) ◽

pp. 119-125

Author(s):

P. J. BENTLEY

Keyword(s):

Urinary Bladder ◽

Water Movement ◽

Short Circuit ◽

Electrical Potential ◽

Short Circuit Current ◽

Toad Bladder ◽

Toad Urinary Bladder ◽

Electrical Potential Difference ◽

Osmotic Gradient

SUMMARY The electrical potential difference and short-circuit current (scc, reflecting active transmural sodium transport) across the toad urinary bladder in vitro was unaffected by the presence of hypo-osmotic solutions bathing the mucosal (urinary) surface, providing that the transmural flow of water was small. Vasopressin increased the scc across the toad bladder (the natriferic response), but this stimulation was considerably reduced in the presence of a hypo-osmotic solution on the mucosal side, conditions under which water transfer across the membrane was also increased. This inhibition of the natriferic response did not depend on the direction of the water movement, for if the osmotic gradient was the opposite way to that which normally occurs, the response to vasopressin was still reduced. The natriferic response to cyclic AMP was also inhibited in the presence of an osmotic gradient. Aldosterone increased the scc and Na+ transport across the toad bladder but this response was not changed when an osmotic gradient was present. The physiological implications of these observations and the possible mechanisms involved are discussed.

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Effects of internal and external pH on amiloride-blockable Na+ transport across toad urinary bladder vesicles

The Journal of Membrane Biology ◽

10.1007/bf01870700 ◽

1985 ◽

Vol 87 (1) ◽

pp. 67-75 ◽

Cited By ~ 18

Author(s):

Haim Garty ◽

Ethan D. Civan ◽

Mortimer M. Civan

Keyword(s):

Urinary Bladder ◽

Toad Urinary Bladder ◽

Na Transport ◽

External Ph

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Use of mass spectrometer to measure CO2 and O2 fluxes in voltage-clamped epithelia

AJP Renal Physiology ◽

10.1152/ajprenal.1979.236.4.f413 ◽

1979 ◽

Vol 236 (4) ◽

pp. F413-F418

Author(s):

S. J. Rosenthal ◽

J. G. King ◽

A. Essig

Keyword(s):

Urinary Bladder ◽

Mass Spectrometer ◽

Ussing Chamber ◽

Electrical Current ◽

Toad Urinary Bladder ◽

Co2 Efflux ◽

Quadrupole Mass ◽

Active Sodium ◽

Na Transport ◽

Made In

A quadrupole mass spectrometer was coupled to an Ussing chamber in order to evaluate rates of oxidative metabolism in voltage-clamped epithelia. Well-defined mixing characteristics of the continuously perfused chamber allowed CO2 and O2 concentrations to be related to rates of CO2 efflux, JCO2, and oxygen influx, JO2. The use of a model tissue to simulate step changes in JCO2 validated the treatment, with response within a minute. Monitoring of metabolism was facilitated by use of a desk-top computer, which evaluated JCO2 at 6-s intervals. Concurrent measurements of electrical current and JCO2 were made in the toad urinary bladder in order to relate active sodium transport to metabolism; the use of amiloride to eliminate active transport and the associated metabolism then allowed evaluation of the rates of active Na transport (JNa) and suprabasal metabolism (JsbCO2), and their ratio JNa/JsbCO2. We report the ability to resolve a 5 pmol/s change in CO2 efflux or an 11 pmol/s change in O2 influx rates.

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Ca(2+)-blockable, poorly selective cation channels in the apical membrane of amphibian epithelia. Tetracaine blocks the UO2(2+)-insensitive pathway.

The Journal of General Physiology ◽

10.1085/jgp.101.1.103 ◽

1993 ◽

Vol 101 (1) ◽

pp. 103-116 ◽

Cited By ~ 3

Author(s):

L Desmedt ◽

J Simaels ◽

W Van Driessche

Keyword(s):

Urinary Bladder ◽

Time Course ◽

Rana Temporaria ◽

Noise Analysis ◽

Inhibitory Effect ◽

The Other ◽

Cation Channels ◽

Toad Urinary Bladder ◽

Amphibian Epithelia ◽

Microelectrode Measurements

We examined the effect of the local anesthetic tetracaine on the Ca(2+)-blockable, poorly selective cation channels in the isolated skin of Rana temporaria and the urinary bladder of Bufo marinus using noise analysis and microelectrode impalements. Experiments with frog skin demonstrated that mucosal concentrations of the compound up to 100 microM did not affect the Na+ current through type S channels (slowly fluctuating, UO2(2+)-blockable channels) and the associated noise. On the other hand, 20 microM mucosal tetracaine already suffices to inhibit approximately 50% of the current carried by Cs+ and Na+ through channel type F (fast fluctuating, UO2(2+)-insensitive channel) and So of the associated Lorentzian component. With 100 microM of the inhibitor the current and So values were reduced by at least 70-80%. The time course of the response to serosal tetracaine was markedly slower and the effects on the current and So were smaller. Possible effects on the basolateral K+ conductance were excluded on the basis of the lack of response of transepithelial K+ movements to 100 microM tetracaine. UO2(2+) and tetracaine together blocked the poorly selective cation pathways almost completely. Moreover, both agents retain their inhibitory effect in the presence of the other. In toad urinary bladder, the Ca(2+)-blockable channel is also tetracaine blockable. The concentration required for half-maximal inhibition is approximately 100 microM in SO4(2-) and approximately 20 microM in Cl-. The data with tetracaine complement those obtained with UO2(2+) and support the idea that the Ca(2+)-blockable current proceeds through two distinct classes of cation channels. Using tetracaine and UO2(2+) as channel-specific compounds, we demonstrated with microelectrode measurements that both channel types are located in the granulosum cells.

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Effects of tetracyclines on aldosterone- and insulin-mediated Na+ transport in the toad urinary bladder

Biochimica et Biophysica Acta (BBA) - Biomembranes ◽

10.1016/0005-2736(79)90254-2 ◽

1979 ◽

Vol 552 (1) ◽

pp. 162-168 ◽

Cited By ~ 3

Author(s):

Malcolm Cox ◽

Joseph Guzzo ◽

Allan Shook ◽

Gary Huber ◽

Irwin Singer

Keyword(s):

Urinary Bladder ◽

Toad Urinary Bladder ◽

Na Transport

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Role of the endogenous kallikrein-kinin system in modulating vasopressin-stimulated water flow and urea permeability in the toad urinary bladder.

Journal of Clinical Investigation ◽

10.1172/jci110219 ◽

1981 ◽

Vol 67 (6) ◽

pp. 1792-1796 ◽

Cited By ~ 20

Author(s):

C P Carvounis ◽

G Carvounis ◽

L A Arbeit

Keyword(s):

Urinary Bladder ◽

Water Flow ◽

Toad Urinary Bladder ◽

Kinin System ◽

Urea Permeability ◽

Kallikrein Kinin System

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Insulin-like growth factor 1 stimulates renal epithelial Na+ transport

AJP Cell Physiology ◽

10.1152/ajpcell.1988.255.3.c413 ◽

1988 ◽

Vol 255 (3) ◽

pp. C413-C417 ◽

Cited By ~ 36

Author(s):

B. L. Blazer-Yost ◽

M. Cox

Keyword(s):

Protein Synthesis ◽

Growth Factor ◽

Urinary Bladder ◽

Classical Model ◽

Na Channel ◽

Toad Urinary Bladder ◽

Insulin Like Growth Factor ◽

Distal Nephron ◽

Na Transport ◽

New Protein

Insulin-like growth factor 1 (IGF1) stimulates vectorial Na+ transport in a classical model of the mammalian distal nephron, the toad urinary bladder. Net mucosal to serosal Na+ flux is stimulated by concentrations of IGF1 as low as 0.1 nM, and the response is maximal at 10 nM. Na+ transport increases within minutes of the serosal addition of IGF1, reaches a maximum in 2-3 h, and is sustained for at least 5 h. Neither the initial nor the sustained response to IGF1 is dependent on a new protein synthesis. The IGF1 response is inhibited by a concentration of amiloride (10(-5) M) that is known to specifically block the conductive apical Na+ channel but that has little effect on the Na+-H+ antiporter. Further studies will be necessary to establish a role for this growth factor in normal renal epithelial function, but it is possible that the natriferic and growth-stimulatory effects of IGF1 are intimately related.

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Tetracycline-induced inhibition of Na+ transport in the toad urinary bladder

AJP Renal Physiology ◽

10.1152/ajprenal.1978.235.4.f359 ◽

1978 ◽

Vol 235 (4) ◽

pp. F359-F366 ◽

Cited By ~ 1

Author(s):

J. Guzzo ◽

M. Cox ◽

A. B. Kelley ◽

I. Singer

Keyword(s):

Urinary Bladder ◽

Short Circuit ◽

Short Circuit Current ◽

Lipid Solubility ◽

Toad Urinary Bladder ◽

Na Transport ◽

Ussing Chambers ◽

Incubation Periods ◽

Active Conductance ◽

Drug Protein Binding

The effects of three tetracyclines, demethylchlortetracycline (DMC), minocycline (MNC), and oxytetracycline (OTC), on Na+ transport (measured as short-circuit current) were examined in toad urinary bladders mounted in modified Ussing chambers. During a 1-h incubation period serosal DMC (but not MNC or OTC) inhibited basal Na+ transport, whereas MNC (but not DMC or OTC) inhibited ADH-stimulated Na+ transport. MNC also inhibited cyclic AMP-stimulated Na+ transport. During longer incubation periods all three drugs inhibited basal Na+ transport. The DMC-induced inhibition of basal Na+ transport and the MNC-induced inhibition of ADH-stimulated Na+ transport were paralleled by an inhibition of the active conductance of the bladders. Thus, although all three drugs inhibit basal Na+ transport, only MNC inhibits ADH-stimulated Na+ transport. This effect does not correlate with the known effects of the tetracyclines on ADH-stimulated water flow or with drug-protein binding, and may be related to the greater lipid solubility of MNC.

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