Concentration dependence of halide fluxes and selectivity of the anion pathway in toad skin

TY - JOUR

T1 - Concentration dependence of halide fluxes and selectivity of the anion pathway in toad skin

AU - Harck, A. F.

AU - Larsen, Erik Hviid

PY - 1986

Y1 - 1986

N2 - The isolated toad (Bufo bufo) skin was mounted under voltage-clamp conditions in a chamber shown to cause no significant edge damage. The serosal side of the skin was bathed with NaCl-Ringer's, and the passive voltage-sensitive anion conductance studied in its fully voltage activated state, V = -80 mV (apical bath negative). The active sodium currents were eliminated by replacing external Na+ with K+. With [Cl-]o varying between 1.45 mM and 110 mM (gluconate substitution) and [I-]o = 3 mM, the total clamping current (y) and the sum of halide currents (x), estimated from flux measurements, were related by y = 1.0x-3.7 microA cm-2 (r2 = 0.98, n = 50 preparations). The increase in [Cl-]o produced a sigmoidal increase in Cl- influx and clamping current, with the rate coefficient for the influx increasing with [Cl-]o for 1.45 less than [Cl-]o less than 60 mM, but decreasing slightly again as [Cl-]o was further raised to 110 mM. A similar relationship was obtained between the rate coefficient for the Br- influx and [Br-]o, and the I- influx and [Cl-]o, indicating that these three ions are transported by a pathway that is activated by Cl-o and Br-o. The rate coefficients for the influxes ranked as follows, I-:Cl-:Br- = 0.7:1:1.3. The I-/Cl- selectivity was shown to be independent of the degree of Cl-o activation of the anion pathway, and identical with the I-/Cl- selectivity of a furosemide-sensitive, conductive pathway. With [Cl-]o, [Br-]o, or [I-]o = 110 mM, the currents ranked as follows, Cl-:Br-:I- = 1:0.68:0.06, indicating that Cl-, to a lesser extent Br-, and I-, poorly activate the conductive anion pathway. External I- was a potent inhibitor of the Cl-o activation of the Cl- conductance. The unidirectional I- fluxes ([I-]o = [I-]i = 3 mM, [Cl-]o = [Cl-]i = 110 mM) revealed passive transport for V less than -50 mV, active transport for V = o mV, and exchange diffusion for V = 50 mV, confirming our previous finding that depending on the transepithelial potential, the toad skin exhibits three modes of anion transport. A model that shares some properties with that of the anion transport system of the red cell membrane accounts for our findings, and for an inwardly directed active Cl- flux in terms of Cl-/HCO3- exchange.

AB - The isolated toad (Bufo bufo) skin was mounted under voltage-clamp conditions in a chamber shown to cause no significant edge damage. The serosal side of the skin was bathed with NaCl-Ringer's, and the passive voltage-sensitive anion conductance studied in its fully voltage activated state, V = -80 mV (apical bath negative). The active sodium currents were eliminated by replacing external Na+ with K+. With [Cl-]o varying between 1.45 mM and 110 mM (gluconate substitution) and [I-]o = 3 mM, the total clamping current (y) and the sum of halide currents (x), estimated from flux measurements, were related by y = 1.0x-3.7 microA cm-2 (r2 = 0.98, n = 50 preparations). The increase in [Cl-]o produced a sigmoidal increase in Cl- influx and clamping current, with the rate coefficient for the influx increasing with [Cl-]o for 1.45 less than [Cl-]o less than 60 mM, but decreasing slightly again as [Cl-]o was further raised to 110 mM. A similar relationship was obtained between the rate coefficient for the Br- influx and [Br-]o, and the I- influx and [Cl-]o, indicating that these three ions are transported by a pathway that is activated by Cl-o and Br-o. The rate coefficients for the influxes ranked as follows, I-:Cl-:Br- = 0.7:1:1.3. The I-/Cl- selectivity was shown to be independent of the degree of Cl-o activation of the anion pathway, and identical with the I-/Cl- selectivity of a furosemide-sensitive, conductive pathway. With [Cl-]o, [Br-]o, or [I-]o = 110 mM, the currents ranked as follows, Cl-:Br-:I- = 1:0.68:0.06, indicating that Cl-, to a lesser extent Br-, and I-, poorly activate the conductive anion pathway. External I- was a potent inhibitor of the Cl-o activation of the Cl- conductance. The unidirectional I- fluxes ([I-]o = [I-]i = 3 mM, [Cl-]o = [Cl-]i = 110 mM) revealed passive transport for V less than -50 mV, active transport for V = o mV, and exchange diffusion for V = 50 mV, confirming our previous finding that depending on the transepithelial potential, the toad skin exhibits three modes of anion transport. A model that shares some properties with that of the anion transport system of the red cell membrane accounts for our findings, and for an inwardly directed active Cl- flux in terms of Cl-/HCO3- exchange.

KW - Animals

KW - Anions

KW - Bufo bufo

KW - Cell Membrane Permeability

KW - Chlorides

KW - Extracellular Space

KW - Female

KW - Galvanic Skin Response

KW - Iodides

KW - Skin Physiological Phenomena

U2 - 10.1111/j.1748-1716.1986.tb07977.x

DO - 10.1111/j.1748-1716.1986.tb07977.x

M3 - Journal article

C2 - 3096079

SN - 0001-6772

VL - 128

SP - 289

EP - 304

JO - Acta Physiologica Scandinavica

JF - Acta Physiologica Scandinavica

IS - 2

ER -