Store-operated channels regulate intracellular calcium in mammalian rods

Area of Science:

• Neuroscience
• Cell Biology
• Ophthalmology

Background:

• Mammalian rod photoreceptors are sensitive to light, and prolonged light exposure can lower intracellular calcium ([Ca(2+)](i)).
• This sustained reduction in [Ca(2+)](i) can lead to light-induced damage and apoptosis in rod cells.
• Understanding calcium homeostasis mechanisms is crucial for protecting photoreceptor function.

Purpose of the Study:

• To investigate protective mechanisms against prolonged cytosolic calcium ([Ca(2+)](i)) lowering in mammalian rods.
• To identify the role of store-operated calcium entry (SOCE) and TRPC1 channels in rod calcium homeostasis.
• To determine the contribution of these pathways to preventing light-induced damage.

Main Methods:

• Depletion of intracellular calcium stores using cyclopiazonic acid in a calcium-free medium.
• Measurement of cytosolic calcium ([Ca(2+)](i)) signals and their modulation by inhibitors (2-APB, SKF 96365, Gd(3+)).
• Analysis of Trpc1 mRNA levels in various retinal dystrophic models and in genetically ablated TRPC1 channel mice.

Main Results:

• Store depletion activated SOCE, leading to a significant increase in [Ca(2+)](i) that was sensitive to SOCE inhibitors.
• SOCE was capable of secondarily activating L-type voltage-operated calcium entry.
• TRPC1 expression was reduced in several rod dystrophic models, but its genetic ablation did not affect SOCE or normal rod function.

Conclusions:

• Store-operated calcium entry (SOCE) is a key mechanism protecting mammalian rods from excessive cytosolic calcium ([Ca(2+)](i)) depletion under sustained light.
• TRPC1 channels are present in mammalian rods and their expression is affected by retinal degeneration, but they are not essential for SOCE or normal rod function.
• These calcium-regulating pathways are vital for maintaining calcium homeostasis and protecting rods from light-induced damage without impairing normal visual function.