Intracellular gradients of ion activities in the epithelial cells of theNecturus gallbladder recorded with ion-selective microelectrodes

Abstract

In Necturus gallbladder epithelial cells the intracellular electrical potential, as recorded with microelectrodes, varied from -28 mV in the mucosal end to about -50 mV in the serosal end of the transporting cell. The Na+ activity varied concurrently from about 39 mM to between 8 and 19 mM. Thus, within the cell both the recorded electrical and chemical gradients caused Na+ to move towards the serosal end. Serosal addition of ouabain (5 X 10(-4) M) caused the intracellular Na+ activity to attain electrochemical equilibrium within 30 min. However, the intracellular electrical potential gradient was only slowly affected. In cells from animals stored at 5 degrees C, the Cl- activity varied from about 55 mM in the mucosal end to 28 mM in the serosal end, and the K+ activity from 50 mM to between 95 and 131 mM. Both ions were close to electrochemical equilibrium within the cytoplasm but were too concentrated to be in equilibrium with the mucosal solution. Bubbling CO2 through the mucosal solution caused the intracellular gradients to vanish. When Na+ in the bathing solutions was exchanged for K+, the intracellular electrical potential became roughly constant at about -5 mV. The Cl- activity became constant in 65 mM, and the K+ activity became constant at 109 mM, both close to equilibrium with the mucosal solution. The Na+ activity was reduced to about 1 mM. The ratio of cytoplasmic resistivities between cells bathed in K+-rich saline to cells bathed in Na+-rich saline was measured by means of triple-barreled electrodes and compared to the same ratio as assessed from the activity measurements. The two values were equal only if one assumes the mobility of Na+ inside the cell to be less than 1/10 of the mobility of K+ or Cl-. The same conclusion was reached by comparing the intracellular Na+ flux calculated from the gradient of electrochemical potential to that flux assess from the net solute absorption. Animals kept at 15 degrees C had lower intracellular Na+ activities, higher Cl- and K+ activities, and higher rates of absorption than animals stored at 5 degrees C. Finally, the degree to which the intracellularly recorded electrical and chemical potentials could reflect an electrode artefact is discussed.

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

“…The general pattern for the intracellular ionic activities, shown in Table 1, confirms previous studies with ion-sensitive micro-electrodes (Zeuthen, 1978;Reuss & Wein-10 Single-barrelled Two batches of animals were used in this work and, as will be described later, they showed clear differences in the rate of fluid transport and active Na extrusion.…”

“…The average activities displayed in Table 1 also confirm previous observations with ion-sensitive micro-electrodes. K and Cl were concentrated inside the cells, whereas Na was at a much lower concentration than predicted from a passive distribution (Zeuthen, 1978(Zeuthen, , 1982Reuss & Weinman, 1979;Graf & Giebisch, 1979;Garcia-Diaz & Armstrong, 1980 (Graf & Giebisch, 1979); (2) the final value of aca recorded in low Na was independent of the initial steady-state activity; (3) aca recovered its initial steady-state value after return to normal Ringer. It appears therefore that virtually all the signal of the micro-electrode was related to Na.…”

Relations between intracellular ion activities and extracellular osmolarity inNecturus gallbladder epithelium

“…Na +" 8-12 raM; CI/-" 31-32 mM; K~ +" 123--113mM; Ec: -50 to -80mV. The Nac + was lower than that obtained by glass microelectrodes (Zeuthen, 1978;Graf & Giebisch, 1979) which recorded 20-40 mM. One explanation is that liquid ion exchanger electrodes cause less damage to the cell wall and consequently less Na § influx.…”

“…Current estimates are of the order 1000-4000f~cm 2 (Fr6mter 1972;Reuss & Finn 1975;1977). This is probably an overestimate (Zeuthen, 1976;Boulpaep & Sackin, 1980;Zeuthen, 1981c) but hardly by three orders of magnitude, although Fr6mter, Suzuki, Kottra & Kampmann (1981) have now found that the resistance of the serosal membrane is as low as 130f2cm 2.…”

Intracellular ion activities in frog skin in relation to external sodium and effects of amiloride and/or ouabain.

“…While these are in agreement with the values found by us on penetrating the basolateral border of isolated epithelia, lower and more variable values were found on penetrating the apical membrane of whole skins (Table 1). This may be due to an ionic gradient through to tissue (Zeuthen, 1978) or to a difference in treatment of the tissue. It may also reflect the apparent compartmentalization ofintracellular potassium (DeLong & Civan, 1978) in epithelial tissues.…”