Analysis of electrical noise in turtle cones.

Area of Science:

• Neuroscience
• Vision Science
• Photobiology

Background:

• Cone photoreceptors are essential for vision, converting light into electrical signals.
• Understanding voltage noise in cones is crucial for elucidating visual processing mechanisms.
• Light-sensitive voltage noise in cones has been previously observed but its precise origins and characteristics remain under investigation.

Purpose of the Study:

• To characterize the properties of light-sensitive voltage noise in turtle retinal cones.
• To determine the relationship between light stimulation, cone hyperpolarization, and noise suppression.
• To investigate the underlying mechanisms and sources of voltage noise in cone photoreceptors.

Main Methods:

• Intracellular recordings were performed on turtle retinal cones (Pseudemys scripta elegans).
• Voltage noise properties, including power density spectra, were analyzed under various light conditions and current injections.
• Noise variance and sensitivity were measured during steady illumination, dim flashes, and light after-effects.

Main Results:

• Light-induced hyperpolarization suppressed cone voltage noise, independent of illumination size or pattern.
• Noise power spectra were often fitted by a product of two Lorentzians, with time constants averaging 40 and 7 msec.
• Noise reduction was observed with hyperpolarizing currents and during steady illumination with moderately bright lights.
• Elementary noise events in isolated cones were estimated to be approximately 100 μV, reflecting unit conductance fluctuations of about 16 pS.

Conclusions:

• The primary source of light-sensitive voltage noise is internal to the cones.
• Noise is postulated to arise from the dynamic gating of light-sensitive ionic channels in the outer segment.
• A residual concentration of a blocking substance in darkness likely closes a fraction of these channels, contributing to the observed noise.