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

Abstract

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)

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

“…(Klemperer et al, 1986b). Similar effects have been observed in split frog skins when serosal C1 was replaced by either SO4 or gluconate (DeLong & Civan, 1984;Giraldez & Ferreira, 1984).…”

“…Sections of abdominal skins of Rana pipiens pipiens, Northern variety, (Connecticut Valley Biological or Kons, Germantown, WI) were mounted horizontally (mucosa up) in an Ussing-type chamber (0.36 cm2), as previously described (Klemperer et al, 1986b). Isolated epithelia were obtained according to the method of Cox and Helman (1983).…”

“…The transepithelial electrical potential V, and the apical membrane potential V,, were measured as described previously (Klemperer et al, 1986b). The use of flowing KCI bridges between the calomel electrodes and the bathing solutions minimized junction potentials.…”

Effects of adrenal steroids on Na transport in the lower intestine (Coprodeum) of the hen

“…1 shows a decrease of Vr and a new steady state, we note an intermediate rise which points to secondary effects. There is evidence, however, from other tissues, that the basolateral membrane is depolarized to a considerable extent (Lewis, Wills & Eaton, 1978;Thompson, Suzuki & Schultz, 1982;DeLong & Civan, 1984;Tang et al, 1985;Klemperer et al, 1986). The marked increase in tissue conductance in the LS group ( Fig.…”

Fast and slow voltage modulation of apical Cl- permeability in toad skin at high [K+]

“…The aim of the present study was to investigate the voltage dependence of the apical Cl -pathway under conditions of high [K + ] Ringer, in which the basolateral membrane of the Cl --transporting cells is presumably depolarized to a high extent and rendered considerably more conductive (20). Under the above conditions, and in the presence of a transepithelial short circuit, it is expected that the apical membrane will also importantly depolarize in the presence of symmetrical KCl Ringer.…”