Effects of external high K+ on Na+ and H+ activities at the posterior cortical layers of rat lens in vitro.
Intralenticular Na+ and rat lens H+ activities (aNa and pHi, respectively) were measured in vitro at the posterior cortical layers of lens fibers using ion-selective microelectrodes. In control HCO(3-)-free solution (K+: 5 mM; external pH (pHo): 7.3), intralenticular potential (Vm) was -61.5 +/- 2.4 mV, aNa was 19.4 +/- 4.6 mM and pHi was 6.90 +/- 0.06 (mean +/- SD). In O-mM K+ solution, Vm slightly depolarized, but aNa and pHi did not change. Increasing K+ concentration to 35 mM induced a large depolarization of Vm, associated with a reduction in aNa and an increase in pHi. pHi was decreased by lowering pHo, but internal acidification thus induced did not show a complete recovery upon reintroduction of a normal solution. The pHi was immediately increased by superfusion with a solution containing 20 mM NH4Cl, and subsequent removal of NH4Cl led to a sustained decrease in pHi. Ouabain and amiloride (a blocker of Na(+)-H+ exchanger) did not exert any effects on aNa or on pHi in normal solution at pHo 7.3. Amiloride applied after the removal of NH4Cl did not alter pHi. These results provide evidence that aNa and pHi at the posterior cortical fiber layers of the rat lens are influenced by Vm, and that, depending on the value of Vm, passive movements of Na+ and H+ can exert direct local effects on pHi and aNa.
Department of Ophthalmology, Kumamoto University Medical School, Japan.
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Takeshita
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Okamura
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Nishi
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects; D007904:Lens Cortex, Crystalline / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D011188:Potassium