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Potassium current oscillations across the rabbit lens epithelium
L J Alvarez1, O A Candia, A C Zamudio
1Department of Ophthalmology, Mount Sinai School of Medicine, 100th Street and 5th Avenue, New York, NY 10029, USA.
Experimental Eye Research
|August 1, 1997
Summary
Spontaneous oscillations in rabbit lens short-circuit current (Isc) are inhibited by calcium channel blockers and potassium channel blockers, but not by Na+-K+ pump inhibitors. These findings suggest voltage-operated calcium and calcium-sensitive potassium channels in the lens epithelium.
Area of Science:
- Ocular Physiology
- Epithelial Transport
- Ion Channel Function
Background:
- Rabbit lenses exhibit spontaneous translens short-circuit current (Isc) oscillations in approximately 30% of isolated lenses.
- Previous characterizations were limited due to the lack of consistent methods to elicit these oscillations.
- Understanding the underlying transport mechanisms is crucial for lens physiology.
Purpose of the Study:
- To further characterize the spontaneous Isc oscillations in rabbit lenses.
- To investigate the role of specific ion channels and calcium homeostasis in these oscillations.
- To explore the electrical potential differences during oscillatory events.
Main Methods:
- Pharmacological inhibition of spontaneous Isc oscillations using various channel blockers (nifedipine, diltiazem, Ba2+, ouabain).
- Assessment of intracellular calcium mobilization agents (thapsigargin, acetylcholine).
- Measurement of translens potential difference (PDt) and individual face PDs under open-circuit conditions.
Main Results:
- Isc oscillations were immediately inhibited by calcium channel blockers (nifedipine, Bay K 8644, diltiazem) and calcium-free conditions.
- Potassium channel blocker Ba2+ also inhibited oscillations, while the Na+-K+ pump inhibitor ouabain did not.
- Intracellular calcium mobilizing agents had transient effects, and oscillations were observed in translens PD (PDt) linked to anterior face PD (PDa) oscillations.
Conclusions:
- Observations support the presence of voltage-operated Ca2+ channels and Ca2+-sensitive K+ channels in the lens epithelial basolateral membrane.
- These channels likely mediate the observed spontaneous oscillatory phenomena.
- A model is proposed to explain the anterior-posterior PD differences during oscillations.