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Opsin exhibits cGMP-activated single-channel activity
1Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06510.
Summary
Purified bovine opsin in liposomes formed cGMP-activated ion channels. These channels exhibited distinct conductances and opening kinetics, suggesting opsin
Area of Science:
- Biochemistry
- Molecular Biology
- Neuroscience
Background:
- Cyclic guanosine monophosphate (cGMP) plays a crucial role in visual transduction.
- Opsin is the apoprotein component of visual pigments like rhodopsin.
Purpose of the Study:
- To investigate the potential of purified bovine opsin to form cGMP-gated ion channels.
- To characterize the properties of these channels.
Main Methods:
- Excised patch-clamp electrophysiology on liposomes reconstituted with purified bovine opsin.
- Varying concentrations of cGMP were applied to observe channel activity.
Main Results:
- Low concentrations of cGMP (10-200 microM) induced reversible single-channel currents.
- Two distinct conductances (32 pS and 17 pS) were identified.
- Channel openings showed mean open times of approximately 1.6 ms and 1.0 ms, with burst durations of 2-3 ms.
- cGMP-activated channel activity was independent of calcium ions (Ca2+).
Conclusions:
- Opsin, or its isoforms/multimers like rhodopsin, may function as a cGMP-modulated ion pore in rod outer segments.
- These findings provide direct evidence for opsin's role in cGMP-dependent ion channel formation.