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Spatial variations in membrane properties in the intact rat lens
1Department of Physiology & Biophysics, State University of New York, Stony Brook 11794-8661.
Biophysical Journal
|August 1, 1992
Summary
This study reveals that the distribution of functional gap junctions, not surface cell conductance, likely directs electrical currents within the rat lens. These findings offer new insights into lens physiology and potential disease mechanisms.
Area of Science:
- Ophthalmology
- Biophysics
- Cell Biology
Background:
- The electrical properties of the eye lens are crucial for its transparency and function.
- Understanding the distribution of electrical conductances within the lens is key to deciphering its physiological mechanisms.
- Previous models have not fully accounted for the spatial variation of electrical properties in the lens.
Purpose of the Study:
- To measure and model the localized electrical properties of the intact rat lens.
- To determine the contributions of surface cell membranes, fiber cell membranes, and gap junctions to lens impedance.
- To investigate the role of gap junction distribution in directing electrical currents and the effects of calcium and acidification on gap junction function.
Main Methods:
- Linear frequency domain impedance measurements at various locations and depths in the rat lens.
- Development of a new electrical model based on lens structure for data analysis.
- Estimation of localized conductances (Gs, gm, Gj) using best-fit solutions.
- Examination of gap junctional uncoupling under elevated calcium and acidic conditions.
Main Results:
- Fiber cell membrane conductance (gm) is uniform (2.02 ± 0.58 µS/cm²).
- Anterior surface conductance (Gs) is 1.26 ± 0.19 mS/cm², posterior is 0.46 ± 0.04 mS/cm², showing a stepwise variation.
- Gap junction conductance (Gj) is uniform in the inner 80% (0.75 S/cm²) but varies smoothly in the outer 20% (0.66–5.95 S/cm²).
- High calcium caused irreversible uncoupling and decreased membrane potential.
- Acidification caused reversible uncoupling in the outer 20% of the lens only.
Conclusions:
- The non-uniform distribution of functional gap junctions, particularly in the lens periphery, is suggested to be the primary factor directing electrical currents.
- Surface cell conductance and Na/K pumps are less likely to be the main drivers of these currents.
- Gap junctions in the inner lens are resistant to acidification, while peripheral gap junctions are sensitive.
- These findings provide a new model for lens electrical properties and current flow.