Transients in toad skin: Short circuit current and ionic fluxes related to inner sodium substitution by monovalent cations

Wa, Varanda; Fl, Vieira

doi:10.1007/bf01869899

Cited by 10 publications

(11 citation statements)

References 36 publications

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“…As was observed by other investigators (e.g. Varanda & Vieira, 1978;Rick et al, 1984), substitution of K for Na causes a drop in L. After a 1-min period gt started to increase, reaching a steady-state value within 10 min. Vo was depolarized in associa- tion with a slight increase in Fo.…”

Section: Effects Of Serosal K (Ci-r1nger's Solutions)supporting

confidence: 53%

Basolateral membrane potential and conductance in frog skin exposed to high serosal potassium

et al. 1986

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In studies of apical membrane current-voltage relationships, in order to avoid laborious intracellular microelectrode techniques, tight epithelia are commonly exposed to high serosal K concentrations. This approach depends on the assumptions that high serosal K reduces the basolateral membrane resistance and potential to insignificantly low levels, so that transepithelial values can be attributed to the apical membrane. We have here examined the validity of these assumptions in frog skins (Rana pipiens pipiens). The skins were equilibrated in NaCl Ringer's solutions, with transepithelial voltage Vt clamped (except for brief perturbations delta Vt) at zero. The skins were impaled from the outer surface with 1.5 M KCl-filled microelectrodes (Rel greater than 30 M omega). The transepithelial (short-circuit) current It and conductance gt = -delta It/delta Vt, the outer membrane voltage Vo (apical reference) and voltage-divider ratio (Fo = delta Vo/delta Vt), and the microelectrode resistance Rel were recorded continuously. Intermittent brief apical exposure to 20 microM amiloride permitted estimation of cellular (c) and paracellular (p) currents and conductances. The basolateral (inner) membrane conductance was estimated by two independent means: either from values of gt and Fo before and after amiloride or as the ratio of changes (-delta Ic/delta Vi) induced by amiloride. On serosal substitution of Na by K, within about 10 min, Ic declined and gt increased markedly, mainly as a consequence of increase in gp. The basolateral membrane voltage Vi (= -Vo) was depolarized from 75 +/- 4 to 2 +/- 1 mV [mean +/- SEM (n = 6)], and was partially repolarized following amiloride to 5 +/- 2 mV.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Effects Of Serosal K (Ci-r1nger's Solutions)supporting

confidence: 53%

Basolateral membrane potential and conductance in frog skin exposed to high serosal potassium

et al. 1986

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“…Skins were equilibrated for approximately 30 rain, and then after every 5 rain all the outer bathing solution was removed by suction into counting vials and immediately substituted by similar fresh solution or by a different solution, according to the experimental protocoI. Special precautions were taken to prevent the effects of skin edge damage on the labeled sucrose efflux, by using hemichambers provided with a circular groove (4 mm wide and 0.4 mm deep, filled with high vaccum silicone grease) located at the internal rim of the hemichamber surface in contact with the epithelial skin surface (Varanda & Lacaz-Vieira, 1978, 1979Bevevino & Lacaz-Vieira, 1981 …”

Section: Methodsmentioning

confidence: 99%

Electrolytes control flows of water across the apical barrier in toad skin: The hydrosmotic salt effect

Benedictis

Lacaz-Vieira

1982

J. Membrain Biol.

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Summary. The reversible dependence of skin osmotic water permeability (Lpo) upon the ionic concentration of the outer bathing solution -which we have called "hydrosmotic salt effect" (HSE) -was studied in the isolated skin of the toad Bufo marinus ictericus. The skin osmotic water flow (Jr) was measured as a function of outer bathing solution osmolality (Oe). Lp~), calculated as (Jv/A ~)ap_ o (where A ~ and AP are the osmotic and hydrostatic pressure differences across the skin, respectively) was constant when O e was altered with sucrose, a nonelectrolyte. In contrast, LpD increased continuously in the hypotonic range as O e was raised from zero (distilled water) with NaC1 or KCI. The HSE could also be evoked in the condition of reversed osmotic volume flow. with the outer bathing medium made hypertonic with sucrose.Diffusional t4C-sucrose permeability, measured in the Jr=0 condition to prevent solvent drag of sucrose in the paracellular pathways, indicate that the hydrosmotic salt effect cannot be explained by assuming a paracellular permeability increase, due to tight junction opening, but might be interpreted as due to changes in the osmotic water permeability of the apical membranes of the most superficial cells of the epithelium.The hydrosmotic salt effect can be elicited in control skins and in vasopressin-stimulated skins, on top of the hormonal response.The time course of the hydrosmotic salt effect is substantially different from that of the hydrosmotic response to vasopressin. Its half-time is 4 to 5 times faster than that of vasopressin action, with individual values as short as 1.5 min.The time courses of the hydrosmotic salt-effect onset and reversibility are exponential, clearly contrasting with the typical sigmoidal shape of vasopressin onset and washout time courses.Based on time course data and on speed of response we postulate that the mechanism underlying the hydrosmotic salt effect is due to modifications of existing water pathways in the apical membrane, rather than to incorporation and removal of water permeability units in this structure.

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“…The same kind of approach was successfully appl!ed to the study of 42K discharge across the same barrier (Varanda & Lacaz-Vieira, 1978Lacaz-Vieira et al, 1979). Obviously, the epithelium being a double barrier series membrane system, we are aware that the results could, in some circumstances, be influenced by the inner barrier or by changes in tight-junction Na permeability, as will be discussed along with the specific points.…”

Section: Discussionmentioning

confidence: 95%

“…These studies were carried out in modified Ussing-Zerahn chambers, according to methods previously described (Varanda & Lacaz-Vieira, 1978. Special precautions were taken to prevent the effect of skin edge damage (Helman & Miller, 1971, 1973Biber & Mullen, 1977) on the low levels of Na efflux by using hemichambers provided with a circular groove (4 mm wide and 0.4 mm deep filled with silicone grease -Dow Coming High Vacuum Grease) located at the internal rim of the hemichamber surface in contact with the epithelial side of the skin (Varanda & Lacaz-Vieira, 1978).…”

Section: Methodsmentioning

confidence: 99%

Control of sodium permeability of the outer barrier in toad skin

Bevevino

Lacaz-Vieira

1982

J. Membrain Biol.

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The 24Na efflux (JNaeff) (i.e., the rate of appearance of 24Na in the outer compartment) in the isolated short-circuited toad skin bathed by NaCl-Ringer's solution on both sides is composed of para- and transcellular components of almost equal magnitudes. This relies on the assumption that amiloride acts on the transcellular component only and could block it completely. Ouabain induces a large transient increase of the transcellular component. This increase, which starts within a few minutes after the addition of ouabain, is due to electrical depolarization of the outer barrier, rather than a consequence of blocking Na recirculation across the inner barrier. The subsequent decline of JNaeff, which takes place after the ouabain-induced JNaeff peak, is due to a progressive block of outer barrier Na channels with time, which can eventually be complete, depending on the duration of action of ouabain. As the external Na concentration was always kept high and constant in these experiments, the results indicate that a rise in cell Na concentration, and not in the outer bathing solution, is the signal that triggers the reduction of outer barrier Na permeability (PNao). Ouabain has no effect upon JNaeff with Na-free solution bathing the outer and NaCl-Ringer's solution the inner skin surface, showing the importance of Na penetration across the outer barrier, and not across the inner barrier due to its low Na permeability, in the process of closing the Na channels of this structure. Step changes from Na 115 mM to Na-free external solution, or vice-versa, may affect both the outer barrier electrical potential difference (PDo) and cell Na concentration (Na)c. Therefore, the behavior of JNaeff depends on which variable (if PDo or (Na)c regulated outer barrier Na permeability) is most affected by step changes in outer bathing solution Na concentration. Amiloride in the control condition blocks the transcellular component of JNaeff. However, in the condition of approximate short-circuiting of the outer barrier and high cellular Na concentration induced by long term effects of ouabain, when the Na channels of the outer barrier are already blocked by elevated cell Na concentration, amiloride may induce the opposite effect, increasing Na permeability of the outer barrier. With outer barrier Na channels completely blocked by high cell Na concentration, PCMB in the outer bathing medium induces a large increase of JNaeff, rendering these channels again amiloride sensitive. The results are consistent with the notion that Na efflux from cell compartment to the outer bathing solution goes through the amiloride-sensitive Na channels of the apical border of the superficial cell layer of toad skin, with an apparent Na permeability modulated by cell ionic environment, most probably the cell Na concentration.

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Transients in toad skin: Short circuit current and ionic fluxes related to inner sodium substitution by monovalent cations

Cited by 10 publications

References 36 publications

Basolateral membrane potential and conductance in frog skin exposed to high serosal potassium

Basolateral membrane potential and conductance in frog skin exposed to high serosal potassium

Electrolytes control flows of water across the apical barrier in toad skin: The hydrosmotic salt effect

Control of sodium permeability of the outer barrier in toad skin

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