Effects of active sodium transport on current-voltage relationship of toad bladder

Civan, MM

doi:10.1152/ajplegacy.1970.219.1.234

Cited by 64 publications

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“…These investigators have obtained evidence consistent with the notion that Na entry into frog skin is diffusional and that the saturating behavior of the entry process is the result of an inverse 11 Biber (1971) reported close agreement between the unidirectional influx of Na across the outer barrier of frog skin and the Isc and these findings have been recently confirmed by Rick, DSrge and Nagel (1975) using a different technique; these findings are consistent with the notion that the unidirectional flux of Na from the inner to the outer solution traverses an extracellular route (Mandel & Curran, 1972) and that entry into the tissue is rectified. Finally, Civan (1970) has provided electrophysiologic evidence for rectification of active Na transport by toad urinary bladder and Saito et al (1974) and Chen and Walser (1975) have arrived at a similar conclusion from studies of isotope fluxes in response to transepithelial PDs. relation between the Na permeability of the outer membrane and the concentration of Na in the outer solution. If the same is true for rabbit colon the absence of a detectable backflux of Na across the mucosal membrane is entirely predictable inasmuch as: (a) As discussed in Appendix I, if Na entry is diffusional the value of E~a =64mV means that the activity of Na in the intracellular Na pool is approximately one-tenth that in the mucosal solution; and (b) ~mc is approximately -30 mV (Table 1).…”

Section: The Effect Of ~M~ On Active and Passive Na Fluxesmentioning

confidence: 70%

Active sodium transport and the electrophysiology of rabbit colon

1977

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The electrophysiologic properties of rabbit colonic epithelial cells were investigated employing microelectrode techniques. Under open-circuit conditions, the transepithelial electrical potential difference (PD) averaged 20 mV, serosa positive, and the intracellular electrical potential (psimc) averaged -32 mV, cell interior negative with respect to the mucosal solution; under short-circuit conditions, psimc averaged -46 mV. The addition of amiloride to the mucosal solution abolishes the transepithelial PD and active Na transport, and psimc is hyperpolarized to an average value of -53 mV. These results indicate that Na entry into the mucosal cell is a conductive process which, normally, depolarized psimc. The data obtained were interpreted using a double-membrane equivalent electrical circuit model of the "active Na transport pathway" involving two voltage-independent electromotive forces (emf's) and two voltage-independent resistances arrayed in series. Our observations are consistent with the notions that: (a) The emf's and resistances across the mucosal and baso-lateral membranes are determined predominantly by the emf (64 mV) and resistance of the Na entry process and the emf (53 mV) and resistance of the process responsible for active Na extrusion across the baso-lateral membranes: that is, the electrophysiological properties of the cell appear to be determined solely by the properties and processes responsible for transcellular active Na transport. The emf of the Na entry process is consistent with the notion that the Na activity in the intracellular transport pool is approximately one-tenth that in the mucosal solution or about 14 mM. (b) In the presence of amiloride, the transcellular conductance is essentially abolished and the total tissue conductance is the result of ionic diffusion through paracellular pathways. (c) The negative intracellular potential (with respect to the mucosal solution) is due primarily to the presence of a low resistance paracellular "shunt" pathway which permits electrical coupling between the emf at the baso-lateral membrane and the potential difference across the mucosal membrane; in the absence of this shunt, the "well-type" electrical potential profile characteristic of rabbit colonic cells would be 'converted' into a "staircase-type" profile similar to those reported for frog skin and toad urinary bladder by some investigators.

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Section: The Effect Of ~M~ On Active and Passive Na Fluxesmentioning

confidence: 70%

Active sodium transport and the electrophysiology of rabbit colon

1977

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“…Even with a constant metabolic requirement for each sodium ion transported actively from cell interior to serosal medium, the ratio of net transepithelial sodium transport (which is what the short-circuit current measures) to COa production would vary as the ratio of sodium entering the cell from the mucosal medium versus that entering via the serosal back leak. On the basis of a close study of the current-voltage relationship in the toad bladder, Civan [1] came to the conclusion that sodium traverses the active pathway largely if not entirely in one direction. However, that study does not rule out the possibility of exchange diffusion.…”

Section: Discussionmentioning

confidence: 99%

Coupling of sodium transport to respiration in the toad bladder

1975

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Energy expenditure and transepithelial sodium transport were measured continuously and simultaneously from isolated urinary bladders of the Dominican toad, Bufo marinus. Sodium transport was measured as the short-circuit current and CO2 produced by the bladder was measured conductometrically by the method of Maffly. The rates of sodium transport and CO2 productions were linearly related. The slope of the regression of sodium transport on CO2 production, dJNa/dJCO2, was found to be quite similar in paired half bladders but to differ significantly between bladders from different toads. Thus, in this preparation there appears to be no unique stoichiometric ratio characterizing sodium transport and metabolism and past efforts to arrive at such a value by averaging results obtained from different animals do not seem warranted. The CO2 production by the isolated bladder which is unrelated to sodium transport was determined by two means: 1) extrapolating the regression of JNa on JCO2 to JNa equals O, and 2) measuring CO2 production with sodium transport suppressed by removal of all sodium from the mucosal bathing medium. The two methods gave values which were in close agreement in each preparationmthis suggests that metabolism which supports nontransport activities in this tissue cannot be recruited to support the energy requirement of sodium transport and vice versa.

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“…4 (cf. Ussing & Windhager, 1964 & Windhager, 1964;Civan, 1970;Helman, O'Neill & Fisher, 1975). We chose to measure R. as the total resistance when the skins were deprived of sodium in the outside solution (Ussing & Windhager, 1964) (V) and Rt was found from the chords in the I-V plane.…”

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confidence: 99%

The effect of external pH on osmotic permeability, ion and fluid transport across isolated frog skin.

Fischbarg¹,

Whittembury²

1978

The Journal of Physiology

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SUMMARY1. The rate of volume flow across frog skin induced by an osmotic gradient was measured when normal (7.4) and low pH (2-28) solutions bathed the outside. The osmotic permeabilities (Pos) were 2-4 + 0-4 and 4 8 + 1.0 ,um/sec, respectively. The change in Po. induced by low pH was reversible.2. Volume flow in the absence of an osmotic gradient was measured at normal and low pH. Values were 0-69 + 0-13 and 1.1 + 0 2 #tl./hr. cm2, respectively; the paired differences were significant (P < 0.0025). This change in rate was partially reversible upon return to normal pH.3. The potential difference (V) and short-circuit current (1I) across skins were measured under several conditions and the following equivalent parameters in a simplified electrical model were computed: total resistance (Rt); shunt resistance (R8); electromotive force of the pump (ENa); and salt transport at open circuit (JNacl). Representative figures were (a), at pH 7 4: Is = 14 + 1*6,A/cm2; Rt = 3.3+0 4 kW. cm2; R8 = 7-2 + 1c0W.cm2; ENa = 103 + 38 mV; JNaCl =-2 + 1.2 ,A/cm2; (b), at pH2-28: Is = 8-3+2-1itA/cm2; Rt = 046+0121cQ.cm2; Rs= 0-65+0-06 kW.cm2;EN. = 59+25mV;JNacl = 94+33 /%A/cm2. 4. From the electrical parameters measured concomitantly with the rate of fluid transport in given experiments, the expected salt concentration of the transported fluid was 0 30 + 0-08 and 0-38 + 0-08 mole/l. at normal and low pH, respectively, or some 3-4 times hyperosmotic with respect to the medium.5. Treatment with low pH on the outside has been found to open the intercellular junctions in previous studies. The present results suggest that, if such an effect occurs, it is localized only to a small fraction of the cell perimeter. Making certain assumptions that fraction could be as low as 0-003.6. Low pH on the outside reversibly changes the electrical parameters of a 'tight' epithelium like the frog skin into values more typical of 'intermediate' epithelia; both the total and shunt resistances decrease to about 0.1 of their normal values.These changes do not apparently affect the osmolarity of the transported fluid.

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Effects of active sodium transport on current-voltage relationship of toad bladder

Cited by 64 publications

References 0 publications

Active sodium transport and the electrophysiology of rabbit colon

Active sodium transport and the electrophysiology of rabbit colon

Coupling of sodium transport to respiration in the toad bladder

The effect of external pH on osmotic permeability, ion and fluid transport across isolated frog skin.

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