The electrical potential profile of gallbladder epithelium

SUMMARY1. Microvillar membrane (Vm) and transmural (Vt) potential differences were measured in proximal colon taken from pigs at birth and up to 10 days of age.2. Vm remained independent of the age of the animal provided it was measured in the absence of methionine. The over-all mean was -43-3 mV. Adding methionine to fluid bathing the mucosal surface of new-born pig colon caused a 9-8 mV depolarization of Vm and a 6-7 mV increase in Vt. These effects, which were Na+-dependent, were not seen in the 10-day-old animal.3. Substituting S042-for Cl-in methionine-free medium caused a hyperpolarization in Vm. Increasing the concentration of K+ caused corresponding depolarization. Substituting choline for Na+ had no effect on Vm. Cl-and K+ movement across the microvillar membrane together account for the bulk of the measured membrane potential. These results apply to all stages of development.4. Na+ uptake across the microvillar membrane of the new-born pig colon was increased in the presence of methionine. This effect disappeared in older animals. Na+ uptake in the absence of methionine doubled during the first 24 h of post-natal life. This increase was maintained using colons taken from older animals.5. Methionine depolarization of Vm in the new-born pig colon is probably caused by the electrogenic influx of Na+. The ability of the colon to actively concentrate methionine within its mucosa disappears at the same time as methionine ceases to affect Vm and Vt. It is suggested that methionine and Na+ form a ternary complex with a carrier in the brush border of the new-born pig colon and that this carrier is lost or modified during early post-natal development.

Section: Discussionmentioning

confidence: 99%

“…-48-3 ±1-3 7-2 + 0-6 -36-6 + 1-2 (35) (4) (34) 1975; Okada, Sato & Inouye, 1975;van Os & Slegers, 1975;Reuss & Finn, 1975).…”

Section: Methodsunclassified

Electrical properties of pig colonic mucosa measured during early post‐natal development.

Hénin¹,

Smith²

1976

“…measurements in gall-bladders by Reuss & Finn (1975a, b), Henin & Cremaschi (1975) and van Os & Slegers (1975) would be that the transepithelial p.d. arises as a difference between ion (mainly K) diffusion p.d.s across the two opposing cell membranes, but modified by the shunt pathway.…”

Section: Effectsmentioning

confidence: 92%

Functional distinction between two transport mechanisms in rabbit gall‐bladder epithelium by use of ouabain, ethacrynic acid and metabolic inhibitors.

Frederiksen¹

1978

SUMMARY1. Net fluid transport rate, transepithelial p.d. and resistance, and unidirectional Na+-fluxes were measured in rabbit gall-bladder preparations exposed on both sides to bicarbonate-Ringer solution in vitro.2. Both ouabain and ethacrynic acid (ETCA) caused dose-dependent decreases of net fluid transport rate; ouabain inhibited fluid transport predominantly from the serosal side, whereas the inhibitory effect of ETCA was elicited mainly from the mucosal (luminal) side. Applied bilaterally, the ID50 for ouabain was 2-5 x 10-6 M, and for ETCA 2-3 x 104 M. After maximal inhibition at each concentration level of the two inhibitors fluid transport could not be reversed.3. 2,4-Dinitrophenol (2,4-DNP) (2 x 104 M) or substitution of 02 by N2 caused an 80% reversible decrease of net fluid transport.4. The spontaneous p.d. across the rabbit gall-bladder was about 2-7 mV, mucosal side positive. 2,4-DNP, N2 and serosal application of ouabain depressed the p.d. after an initial hyperpolarization. This decrease was reversible during recovery from 2,4-DNP and N2, but irreversible after removal of ouabain at concentrations > 10-4 M. Mucosal application of ETCA (10-3 M) caused no decrease in p.d., which actually increased slightly.5. Calculated passive serosal-to-mucosal Na+-fluxes changed in the same direction as did changes in conductance.6. It is concluded that ETCA does not interfere primarily with the Na-K-ATPase or cellular oxidative metabolism. The data support the proposal that the pump responsible for isosmotic transepithelial fluid transfer is located in the luminal end of the cells. This pump is ETCA-sensitive. The ATPase-dependent Na-K pump, which can be inhibited by ouabain, is localized in the serosa-facing cell membrane. The data suggest that the inhibition of net fluid transport by ouabain is indirect and mediated by changes in intracellular ion concentrations.7. The results support the concept that the transepithelial fluid transport mechanism is electroneutral, and suggest that the mucosa positive transepithelial p.d. is due to differences in electromotive forces arising from ion (mainly K+) diffusion across the mucosal and serosal cell membranes. FREDERIKSEN

“…There are in principle two parallel pathways available for the transport of salt and water in leaky epithelia, namely cellular and paracellular, and recent evidence suggests that the movement ofwater occurs mainly through a paracellular route (Hill & Hill, 1978 b; Whittembury, Verde de Martinez, Linares & Paz-Aliaga, 1980;Steward, 1982). Since it is well established that the intercellular junctions are highly permeable to monovalent cations (Fromter, 1972;Reuss & Finn, 1975;Van Os & Slegers, 1975) the question then arises as to whether the main route for the transport of Na during fluid absorption is transcellular or paracellular. The point might be relevant not only to the mechanism of Na transport but to the conditions under which the movements of water occur.…”

Section: Introductionmentioning

confidence: 99%

“…The point might be relevant not only to the mechanism of Na transport but to the conditions under which the movements of water occur. There is no direct information on this problem, and the comparison between estimates of cell and transepithelial Na transport rates in Necturus gallbladder has led different authors to draw opposite conclusions (Graf & Giebisch, 1979; Van Os & Slegers, 1975;Hill, 1981).…”

Section: Introductionmentioning

confidence: 99%

Active sodium transport and fluid secretion in the gall‐bladder epithelium of Necturus.

Giráldez¹

1984

SUMMARY1. Intracellular Na, K and Cl activities (ac8, ac and ac1) and membrane potentials were measured in Necturus gall-bladder epithelium using double-barrelled ion-sensitive micro-electrodes. Mucosal membrane potential was about -55 mV and the mean control activities were aca = 14-7 mm, ac = 91-6 mm and ac1 = 20-3 mM.2. Replacing mucosal Na by K caused a fall in aca that followed an exponential time course. The rate of change in aea was linearly related to aca above a certain value (-3 mm). ac and ac, both increased in K Ringer solution. From the change in all three ions the cell was estimated to swell at an initial rate of 0-13 % s-1. From the initial rate of change in aca, a net cell efflux of Na of 405 pmol cm-2 s-1 was calculated. Replacement of Na by Tris or choline led to a similar result. The transepithelial Na transport rate was for this group of animals 346 pmol cm2 s .3. Ouabain (10-3 M) produced an increase in aca and ac1, whereas ac decreased. The cells were estimated to swell at an initial rate of 0-06 % s-1. The initial Na influx after Na-pump inhibition was calculated to be 162 pmol cm-2 s-1. The parallel measure ofthe transepithelial rate oftransport ofNa gave a value of 189 pmol cm-2 s-1. Ouabain inhibited the decrease in aca after replacement of Na by K by about 80 %. 4. A fast depolarization, ranging from 2 to 7 mV, occurred after the perfusion with ouabain. Em then slowly decreased from about 53 to 32 mV in 1 h. 5. It is concluded that (a) the major fraction of the transepithelial transport of Na is transcellular and mediated by the Na pump, (b) the pumping rate is linearly dependent on internal Na within a certain range and (c) the Na pump is electrogenic under normal circumstances.