Influence of serosal Cl on transport properties and cation activities in frog skin

Abstract

The effects of serosal substitution of isosmotic Na2SO4-Ringer solution for NaCl-Ringer solution were studied in the short-circuited frog skin (Rana pipiens, Northern variety). Despite prompt changes of transepithelial measurements, initial cellular effects were slight. After 30 to 45 min, however, the transcellular current had decreased and the cell electrical potential had depolarized, in association with decrease of the apical membrane fractional resistance and basolateral membrane conductance. Apical membrane slope conductance was unaffected. Similar effects were obtained with isolated epithelia. With the use of gluconate or NO3 in place of Cl, the effects on cellular current and conductance were minimal or insignificant, despite changes of the cell potential, fractional resistance, and basolateral conductance similar to those seen with sulfate. Following prolonged exposure to serosal SO4-Ringer, the extent of depolarization induced by raising the serosal K concentration decreased, indicating diminution of basolateral K conductance and the existence of other basolateral conductances. Equilibration in serosal gluconate-Ringer enhanced polarization on serosal restoration of Cl or removal of Na, again indicating a time-dependent change in the basolateral conductance pattern. Depolarization on removal of serosal Cl was not attributable to inhibition of the pump. Nor was it the result of decrease of the K equilibrium potential EK: exposure to serosal SO4-Ringer decreased cell K activity aKc from 104 +/- 6 to 58 +/- 4 mM (n = 5), but EK was reduced only slightly; exposure to serosal gluconate increased aKc and EK. Serosal sulfate lowered the cell Na activity aNac, but the electrochemical potential difference for Na across the apical surface was unaffected. The concurrent decrease of both aKc and aNac following serosal substitution of SO4 for Cl raises questions concerning mechanisms of osmoregulation.

K+ secretion across frog skin. Induction by removal of basolateral Cl-.

“…Response to O-Clb. Previous studies have shown that 0-Clb depolarizes the apical membrane during the same period that we observed induction of K ÷ secretion (Biber et al, 1985;Duffey et al, 1986;Costa et al, 1987;Klemperer and Essig, 1988; Leibowich et al, 1988). Thus it seemed reasonable that under control conditions, with large negative intracellular voltages (Nagel, 1976;Helman and Fisher, 1977), K ÷ secretory rates are extremely low because K ÷ is near electrochemical equilibrium across the apical membrane, and exposure to 0-Clb could "induce" K ÷ secretion simply by depolarizing the cell, thereby favoring K ÷ exit.…”

“…There are four known effects of 0-Clb on principal cells: (a) intracellular voltage depolarizes (see above; Biber et al, 1985;Duffey et al, 1986;Costa et al, 1987;Klemperer and Essig, 1988;Liebowich et al, 1988); (b) intracellular [CI-] and [Na ÷] decrease (Ferreira and Ferreira, 1981;Giraldez and Ferreira, 1984;D~Jrge et al, 1985;Biber et al, 1985); (c) cell volume is reduced (Ussing, 1965;Ferreira and Ferreira, 1981); and (d) intracellular pH rises (Civan and Peterson-Yantorno, 1986). Any or all of these could play a role in the induction of K ÷ secretion.…”

Effects of Serosal Hypotonicity and Anion Substitutions on Apical and Basolateral K⁺ Conductances

“…and fR" GbK G ash + G hK ( 8) GaK, GaSh. GbK and Gp were calculated with equations 5-8 from experimental values for G t and fRn recorded in the absence and presence of Ba2+.…”

“…This long-time increase does not occur in gluconate solutions and depends on the presence of Cl" in the serosal bath and on the tonicity of the serosal solu tion. Effects of serosal tonicity and Cl" re placements on transepithelial Na+ transport have been the subject of several studies [7][8][9][10]. Microelectrode experiments [7][8][9] showed that a major part of the inhibition on Na+ transport following Cl" removal or after elevation of the serosal osmolality could be attributed to cell depolarization.…”

“…The K+ pathways in this tissue resemble those in the distal part of the neph ron [18. 19] and are involved in the secretion of K+ [3][4][5]19], The basolateral membranes of the epithelium of frog skin have a signifi cant electroneutral permeability for Cl" [8,20], whereas the apical membranes of the granulosum cells are impermeable for the an ion [20,21]. Serosal replacement of the im permeable anion gluconate by Cl" will result in an increase of cellular Cl" and in an ex panded cellular volume [ 10,13].…”