Bicarbonate secretion and non‐Na component of the short‐circuit current in the isolated colonic mucosa of <i>Bufo arenarum</i>

Carlisky, N.J.; Lew, Virgilio L.

doi:10.1113/jphysiol.1970.sp009029

Cited by 27 publications

(5 citation statements)

References 8 publications

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“…For simplicity, the models assume a single barrier to transport from lumen (L) to blood (B). In all likelihood, the H and HCO3 ions are produced by intracellular hydration of CO2 (Carlinsky & Lew, 1970) which is consistent with the high levels of carbonic anhydrase in colonic mucosa (Carter & Parsons, 1971). All values are expressed in pequiv/cm2 .…”

Section: Discussionsupporting

confidence: 72%

Effect of Escherichia coli heat‐stable enterotoxin, cholera toxin and theophylline on ion transport in porcine colon

Argenzio

Whipp

1981

The Journal of Physiology

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SUMMARY1. The effect of heat-stable enterotoxin (ST) of Escherichia coli, cholera toxin (CT), and theophylline (a phosphodiesterase inhibitor) on ion and water transport was studied with an in vivo isolated loop system of the pig colon.2. All three agents abolished net Na absorption as a result ofa decrease in the lumen to blood Na flux alone. With all three agents, net Cl absorption was reduced, but not abolished, and net HCO3 secretion was elicited. Luminal Pco, was reduced with CT and theophylline from that observed in normal Ringer alone.3. Theophylline resulted in a prompt and sustained increase in both cyclic adenosine monophosphate (cyclic AMP) and cyclic guanosine monophosphate (cyclic GMP) levels in colonic mucosa studied in vitro. ST selectively elevated cyclic GMP, whereas CT selectively elevated cyclic AMP. These responses paralleled the time course and magnitude of response of the transepithelial electrical potential difference (V*LB) measured in vivo.4. Ion replacement studies in the presence or absence of theophylline showed that in the absence of Na, Cl absorption was slightly reduced and HCO3 secretion was elicited; no further additive effects of theophylline in the absence of luminal Na were observed. In the absence of luminal Cl, net Na absorption was abolished and HCO3 was absorbed; theophylline resulted in significant net Na and HCO3 secretion.

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Section: Discussionsupporting

confidence: 72%

Effect of Escherichia coli heat‐stable enterotoxin, cholera toxin and theophylline on ion transport in porcine colon

Argenzio

Whipp

1981

The Journal of Physiology

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“…The lack of complete identity between the total I~c and net Na absorption has been a consistent observation studies of the amphibian colon [-3, 5, 6, 7, 20]. Carlinsky and Lew [3] suggested that the nonsodium portion of the I~ in the colon of Bufo arenarum was due to HCO 3 secretion from an intra- …”

Section: Na Fluxes and The Source Of The Short-circuit Currentmentioning

confidence: 83%

Na and Cl transport across the isolated turtle colon: Parallel pathways for transmural ion movement

Dawson

1977

J. Membrain Biol.

102

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Summary. Transmural fluxes of 3H-mannitol and 22Na or a6CI were measured simultaneously in portions of isolated turtle colon stripped of serosal musculature. The relationships between mannitol flux and the flux of Na or C1 are characteristic of simple diffusion and suggest that transmural mannitol flow is largely confined to a paracellular pathway where Na, C1 and mannitol move much as in free solution. The contribution of"edge damage" to the transmural mannitol flow appears to be minimal. Mucosal hyperosmolarity causes "blisters" in epithelial tight junctions and increases the diffusional permeability to Na and mannitol, suggesting that the rate-limiting barrier in the shunt path is the tight junction. If the total mucosa to serosa flux of Na is corrected for the portion traversing the shunt pathway it is apparent that changes in the short-circuit current are completely accounted for by the mucosa to serosal movement of Na through a cellular path. In addition, the serosa to macosa flux of Na appears to be restricted to the shunt. These observations suggest that there is no appreciable "backflux" of Na through the active, cellular path. In the presence of 10-4 M amiloride the short-circuit current is markedly reduced and the mucosa to serosa Na flux is restricted to the shunt, so that the net Na flux is abolished. The small amiloride-insensitive short-circuit current is consistent with HCO 3 secretion. Mucosa to serosa and serosa to mucosa fluxes of C1 appear to be largely restricted to the paracellular shunt path and there is no evidence for any net flow of C1 under short-circuit conditions. The total tissue conductance can be described as the sum of three components: a shunt conductance which is linearly related to the transmural mannitol flow, an "active" conductance which is linearly related to the short-circuit current and a small residual conductance. The shunt conductance is attributable to the diffusive movements of Na and C1 through the paracellular path. Variations in the active Na transport from tissue to tissue are largely attributable to variations in the apparent conductance of the active Na transport path. The driving force for active Na transport can be described as an apparent emf of approximately 130 mV. These results suggest that transmural mannitol flux provides a quantitative estimate of the ion permeability and electrical conductance of a paracellular shunt path across the isolated turtle colon and thereby facilitates the study of the transport characteristics and electrical properties of cellular paths for transepithelial solute movement.The simplest model which can account for the transport properties of an epithelial cell layer is one which allows for two parallel paths for transmural solute and water flow, one through the cells and another between

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“…If the Na ions that are actively transported towards the serosal surface come from an intracellular compartment that exchanges slowly with the Na ions present in the mucosal solution, the rate at which isotope enters the serosal solution will underestimate the true mucosa-toserosa Na flux since the Na is coming from a Na pool that has not yet reached the specific activity of the Na in the mucosal solution, but is slowly approaching it. However, this situation can be ruled out for the following reason: 1 cm2 of membrane has an average wet weight of about 23 mg (Carlisky & Lew, 1970); the superficial layer of epithelial cells, which are the only cells involved in the active processes discussed here, contribute not more than 10 % of the total weight of the membrane. If the intracellular concentration of Na is supposed to be 65 m-equiv/kg and if the Na is equally distributed among the different types of cell, the total amount of Na inside the epithelial cells of 1 cm2 526 V. L. LEW IONIC FLUXES IN ISOLATED TOAD COLON of membrane is 0 13 ,t-equiv.…”

Section: Discussionmentioning

confidence: 94%

Short‐circuit current and ionic fluxes in the isolated colonic mucosa of Bufo arenarum

Lew¹

1970

The Journal of Physiology

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SUMMARY1. The unidirectional fluxes of 22Na, 36CI and [14C]bicarbonate ions were measured in paired portions of the isolated and short-circuited colonic mucosa of Bufo arenarum, separated from its muscular layer. Pharmacological effects as well as effects of changes in the composition of the nutrient solutions on the electrical parameters of membrane activity (potential difference, short-circuit current and total membrane resistance) are described.2. The net fluxes of both Cl and bicarbonate ions were not significantly different from zero in the absence of electrochemical gradients across the membrane.3. The net Na flux from mucosa to serosa represented a variable proportion of the short-circuit current ranging from 62 to 100 %.4. The proportion of membranes with high discrepancies between net Na flux and short-circuit current decreased with the duration of captivity of the toads.5. When Na was entirely replaced by choline in the mucosal bathing solution, the short-circuit current dropped by a variable amount within the range of 64 to 98 % of its control values in different membranes. This effect was completely reversible. Similar changes in the serosal solution had no effect.6. The short-circuit current and potential difference were very sensitive to the serosal concentration of bicarbonate ions. In different membranes, 60-100 % of the short-circuit current was reversibly abolished by bathing the serosal surface with a bicarbonate-free solution. The mucosal bicarbonate level had no effect on either the potential difference or the shortcircuit current. 5 mm bicarbonate in the serosal solution restored at least * Present address: Physiological Laboratory, Downing Street, Cambridge, England. 50 % of the short-circuit control value and full recovery was attained by concentrations near 30 mm bicarbonate.7. Anoxia brought the potential difference and short-circuit current reversibly down to zero in about 50 min.8. Ouabain reduced the short-circuit current up to 80 % in about 40 min when present in the serosal solution at a concentration of 10-4 M. At this or lower concentrations the ouabain effect was reversible. Above this level ouabain produced 100% inhibition in 3-4 hr, but this was no longer reversible. Ouabain had no effect on the short-circuit current either when applied to the mucosal surface or in the absence of Na from the mucosal solution.9. Diamox produced a variable inhibition of the short-circuit current of up to 30 % only at concentrations above 10 mm.10. Possible mechanisms are discussed for the appearance of the non-Na component of the short-circuit current. A theory concerning its nature is proposed.

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Bicarbonate secretion and non‐Na component of the short‐circuit current in the isolated colonic mucosa of Bufo arenarum

Cited by 27 publications

References 8 publications

Effect of Escherichia coli heat‐stable enterotoxin, cholera toxin and theophylline on ion transport in porcine colon

Effect of Escherichia coli heat‐stable enterotoxin, cholera toxin and theophylline on ion transport in porcine colon

Na and Cl transport across the isolated turtle colon: Parallel pathways for transmural ion movement

Short‐circuit current and ionic fluxes in the isolated colonic mucosa of Bufo arenarum

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