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

Abstract

Intracellular activities of Na+, K+ and Cl-, .**GRAPHIC**. .**GRAPHIC**. and .**GRAPHIC**. were measured with ion-selective single-, double- and triple-barrelled micro-electrodes in skin and isolated epithelia of Rana temporaria bathed on both sides with normal or modified physiological saline. Apical and basolateral membrane potentials, .psi.ac and .psi.cs and resistance Ra and Rb, respectively, were also measured and from the latter the fractional resistance of the apical membrane, F(Ra) and voltage divider ratio, .DELTA..psi.ac/.DELTA..psi.cs were measured as criteria of satisfactory membrane penetration by the micro-electrodes. Under control conditions, .**GRAPHIC**. was 12.3 .+-. 0.8 mM, .**GRAPHIC**. was 70.3 .+-. 2.2 mM and .**GRAPHIC**. was 20.3 .+-. 1.6 mM with .psi.ac averaging -38.0 .+-. 3.2 mV. When 10-4 M-amiloride was added to the apical bathing fluid .**GRAPHIC**. fell within 10 min to 1.18 .+-. 0.1 mM and .**GRAPHIC**. to 5.2 .+-. 0.9 mM, while .**GRAPHIC**. increased to 86.2 .+-. 3.8 mM as measured from the basolateral border of isolated epithelia. The Na transport pool of the skin was measured from the fall in .**GRAPHIC**. in the presence of amiloride and could be expressed as 33 .times. 10-9 mol/cm2 of epithelium. The mean rate of fall of .**GRAPHIC**. under these conditions correspond to an efflux rate at the basolateral border of 30.1 .times. 10-9 mol/cm2 per min .times. (48 .mu.A/cm2) giving a half-time for turnover of the Na transport pool of 33 s. Reduction of Na concentration in the apical fluid from the normal 79 mM-Na to 10, 1 and 0.1 mM caused .**GRAPHIC**. to fall in stages to 2 mM. Because .psi.ac increased in negativity to -101 mV in the process, this driving force for passive Na accumulation more than offset the increased Na gradient opposing Na influx across the apical border.