Contribution from a pH- and tonicity-sensitive K+ conductance to toad translens short-circuit current.
Studies of toad (Bufo marinus) lenses mounted in Ussing-type chambers revealed that: (1) the translens short-circuit current (Isc) across the posterior surface is primarily carried by the movement of Na+ from the posterior bathing solution to the lens; (2) across the anterior face the majority of the Isc is mediated by Ba(2+)-sensitive channels and the remaining current is rapidly reduced by ouabain; (3) most of the anterior K+ conductance is of the tonicity-sensitive, quinidine-inhibitable type (i.e. hypotonic shifts increase Isc and hypertonic shifts decrease Isc; quinidine pretreatment eliminates such responses); (4) 86Rb+ uptake is stimulated by alkaline pH and occurs primarily across the anterior surface with quinidine the most potent inhibitor of this process; and (5) the Na(+)-K+ pump can maintain lens [Na+] and [K+] for at least 20 hr in a Ringer's solution near neutral pH but not at pH 8.7 (a pH used in some studies with this lens). It is concluded that the Isc can be viewed as a representation of the current across the epithelial basolateral membrane, a surface dominated by pH- and tonicity-sensitive K+ channels. The direction of the Isc response to tonicity changes suggests a role for these channels in epithelial volume regulation.
Alvarez
L J
LJ
Department of Ophthalmology, Mount Sinai School of Medicine, New York, NY 10029.
Wolosin
J M
JM
Candia
O A
OA
D000818:Animals; D001464:Barium / Q000502:physiology; D002024:Bufo marinus; D006863:Hydrogen-Ion Concentration; D007908:Lens, Crystalline / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D008985:Monensin / Q000494:pharmacology; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D011802:Quinidine / Q000494:pharmacology; D012413:Rubidium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism
D015221:Potassium Channels; D001464:Barium; D008985:Monensin; D012964:Sodium; D011802:Quinidine; D012413:Rubidium; D011188:Potassium