Effect of Ba2+ on the K+ conductance pathways in the frog cornea.
Two types of transepithelial potential difference (PD) responses have been observed in the bullfrog, Rana catesbeiana, when the K+ concentration is changed in the aqueous solution. (1) A normal response, that is, a decrease in the positivity of the aqueous solution when the K+ is increased in this solution. (2) An anomalous response, that is, an increase in PD when K+ is increased from 0 to 4 mM in the aqueous solution. In present experiments 2 mM Ba2+ results in a significant decrease in transepithelial PD and an increase in resistance (R), consistent with the well-known effect of Ba2+ on the K+ conductance in other biological membranes. In the presence of Ba2+ compared to its absence the normal PD responses were decreased when K+ was increased from 4 to 20 or to 79 mM in the aqueous solution. Barium enhanced, but not significantly, the anomalous PD response (PD increase) when K+ was increased from 0 to 4 mM. An anomalous PD response (PD decrease) was obtained with Ba2+ when K+ was changed from 4 to 0 mM while in its absence the response was normal (PD increase) or did not change. These findings support the concept that anomalous PD responses as a result of the electrogenic (Na+ + K+)-ATPase may be obtained when the resistance of the simple K+ pathway is increased.
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Carrasquer
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Rehm
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Schwartz
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D003315:Cornea / Q000187:drug effects / Q000502:physiology*; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000502:physiology*; D011892:Rana catesbeiana
D007473:Ion Channels; D001464:Barium; D011188:Potassium