Ba2+-induced changes in the Na+- and K+-permeability of the isolated frog skin.
Addition of the K+-channel blocking agent Ba2+ to the basolateral solution (in a concentration which is assumed to block the K+-flux via the K+-channels completely) resulted initially in a two-thirds reduction in the short-circuit current (SCC), followed by a complete recovery of the SCC. To examine the reason for this recovery, experiments were carried out which made it possible to calculate the Na+-permeability of the apical membrane (PaNa) and the K+-permeability of the basolateral membrane (PbK). The presence of Ba2+ had no significant effect on the cell volume and the cellular Na+- and K+-concentration. Addition of Ba2+ resulted in a depolarization of the intracellular potential (VSCC) from a control value of -76.3 +/- 2.8 mV to -15.1 +/- 1.7 mV. Although a complete recovery in the SCC was observed, VSCC did not recover. The K+-flux across the basolateral membrane was estimated from washout experiments. The washout of 42K+ (the K+-efflux) could be described by a single exponential component with a half time of 30-70 min. The addition of Ba2+ during the washout resulted in a transient decrease in 42K+-efflux from the epithelium. From VSCC and the cellular K+ and Na+-concentration and the coupling ratio of the Na-K pump, it was found that Na+-permeability of the apical membrane was 6.5 X 10(-7) cm X s-1 before the addition of Ba2+ and 1.7 X 10(-6) cm X s-1 when the SCC had recovered after the addition of Ba2+ and PbK changed from 8.8 X 10(-6) cm X s-1 to 1.5 X 10(-6) cm X s-1. Thus, the observed recovery in SCC was due to a considerable increase in Na+-permeability of the apical membrane and the presence or appearance of a small Ba2+-insensitive K+-permeability in the basolateral membrane.
Nielson
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D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects*; D004848:Epithelium / Q000378:metabolism; D005260:Female; D007425:Intracellular Membranes / Q000187:drug effects; D007473:Ion Channels; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D011896:Rana temporaria; D012867:Skin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000187:drug effects
D007473:Ion Channels; D001464:Barium; D012964:Sodium; D011188:Potassium