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Calcium regulation by lens plasma membrane vesicles
Archives of Biochemistry and Biophysics
|August 1, 1988
Summary
The plasma membrane regulates lens cell calcium levels through ATP-dependent pumps and Na:Ca exchange carriers. Impaired calcium transport, due to -SH group oxidation, may contribute to cataract formation.
Area of Science:
- Ophthalmology
- Cell Biology
- Biochemistry
Background:
- Lens fiber cell cytosolic calcium concentration is critical for transparency.
- Dysregulation of calcium homeostasis is implicated in cataract development.
Purpose of the Study:
- To investigate the role of the plasma membrane in regulating cytosolic calcium in lens fiber cells.
- To characterize the mechanisms of calcium uptake and release in lens vesicles.
Main Methods:
- Utilized vesicular preparations from calf lenses to study calcium transport.
- Employed ATP-dependent assays, ionophores (A23187), and inhibitors (vanadate, R24571) to analyze calcium handling.
- Investigated the effects of potassium, cAMP-dependent protein kinase, valinomycin, selenite, and p-chloromercuribenzoate on calcium transport.
Main Results:
- Demonstrated ATP-dependent calcium accumulation in vesicles, indicating active transport into a vesicular space.
- Identified a calmodulin-dependent, vanadate-sensitive calcium pump on the plasma membrane.
- Showcased Na+-dependent calcium release via a Na:Ca exchange carrier.
- Revealed the involvement of essential -SH groups in both calcium uptake and release mechanisms.
Conclusions:
- Lens fiber cell cytosolic calcium is regulated by multiple plasma membrane transport systems.
- The sensitivity of these systems to -SH reagents suggests a role in cataractogenesis, potentially through protein oxidation and altered calcium homeostasis.