Implications of an anomalous intracellular electrical response in bullfrog corneal epithelium |
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Authors: | Peter Reinach Wolfram Nagel |
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Institution: | (1) Department of Ophthalmology and Physiology & Biophysics, Washington University School of Medicine, 63110 St. Louis, Missouri;(2) Physiologisches Institut, Universitat Munchen, Munich, West Germany |
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Abstract: | Summary The ionic dependencies of the transepithelial and intracellular electrical parameters were measured in the isolated frog cornea. In NaCl Ringer's the intracellular potential differenceV
sc measured under short-circuit conditions depolarized by nearly the same amount after either increasing the stromal-side KCl concentration from 2.5 to 25mm or exposure to 2mm BaCl2 (K+ channel blocker). With Ba2+ the depolarization of theV
sc by 25mm K+ was reduced to one-quarter of the control change. If the Cl-permselective apical membrane resistanceR
o remained unchanged, the relative basolateral membrane resistanceR
i, which includes the lateral intercellular space, increased at the most by less than twofold after Ba2+. These effects in conjunction with the depolarization of theV
sc by 62 mV after increasing the stromal-side K+ from 2.5 to 100mm in Cl-free Ringer's as well as the increase of the apparent ratio of membrane resistances (a=R
o/Ri) from 13 to 32 are all indicative of an appreciable basolateral membrane K+ conductance. This ratio decreased significantly after exposure to either 25mm K+ or Ba2+. The decline ofR
o/Ri with 25mm K+ appears to be anomalous since this decrease is not consistent with just an increase of basolateral membrane conductance by 25mm K+, but rather perhaps a larger decrease ofR
o thanR
iAlso an increase of lateral space resistance may offset the effect of decreasingR
i with 25mm K+. In contrast,R
o/Ri did transiently increase during voltage clamping of the apical membrane potential differenceV
o and exposure to 25mm K+ on the stromal side. This increase and subsequent decrease ofR
o/Ri supports the idea that increases in stromal K+ concentration may produce secondary membrane resistance changes. These effects onR
o/Ri show that the presence of asymmetric ionic conductance properties in the apical and basolateral membranes can limit the interpretative value of this parameter. The complete substitution of Na+ withn-methyl-glucamine in Cl-free Ringer's on the stromal side hyperpolarized theV
sc by 6 mV whereas 10–4
m ouabain depolarized theV
sc by 7 mV. Thus the basolateral membrane contains K+, Na+ and perhaps Cl– pathways in parallel with the Na/K pump component. |
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Keywords: | corneal epithelium frog chloride transport potassium conductance apical and basolateral membranes barium ouabain |
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