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Influence of calmodulin antagonists on Ca2+ transport in the lens
Abstract:
Attempts were made to elucidate the relation between lens opacification resulting from inhibition of Ca2+ transport and high calcium accumulation in the lens. Mouse lenses were incubated with naphthalenesulfonamide compounds (W-5, W-7, W-12 and W-13) which act as calmodulin antagonists. When lens Ca2+-ATPase activity was inhibited by those calmodulin antagonists, an accumulation of calcium in the lens was observed. This phenomenon depended on the chemical structure of calmodulin antagonist. In lenses treated with W-7, more than 97% of excess calcium was bound. Insoluble protein increased from 8.5 to 17% of the total protein and the degree of lens opacification increased to 85.1%. These results suggested that dysfunction of the Ca-pump system leads to calcium accumulation, thus in turn inducing protein denaturation which in turn is followed by lens opacification.
Insights
Calmodulin antagonists inhibit calcium transport in mouse lenses, causing calcium buildup and protein denaturation. This leads to significant lens opacification, suggesting Ca-pump dysfunction causes cataracts.
Area of Science:
- Ophthalmology
- Biochemistry
- Cell Biology
Background:
- Lens opacification (cataract) is linked to calcium transport.
- Calcium accumulation in the lens is a key factor in cataract formation.
Purpose of the Study:
- To investigate the relationship between inhibited calcium transport and lens opacification.
- To understand the role of calmodulin antagonists in calcium accumulation and cataract development.
Main Methods:
- Mouse lenses were incubated with various naphthalenesulfonamide compounds (calmodulin antagonists).
- Calcium levels, Ca2+-ATPase activity, insoluble protein content, and lens opacification were measured.
Main Results:
- Inhibition of Ca2+-ATPase activity by calmodulin antagonists led to significant calcium accumulation in the lens.
- Calcium accumulation and subsequent lens opacification were dependent on the chemical structure of the antagonist.
- Treatment with W-7 resulted in over 97% of excess calcium binding and increased insoluble protein to 17%, with 85.1% lens opacification.
Conclusions:
- Dysfunction of the lens calcium pump system induces calcium accumulation.
- Calcium accumulation leads to protein denaturation, ultimately causing lens opacification.
- Calmodulin antagonists provide a model for studying calcium-induced cataractogenesis.