Biomaterial Database

Changes in time scale and sensitivity in turtle photoreceptors. 1974

D A Baylor, and A L Hodgkin

1. In turtle cones the steady-state relation between the internal potential and log light intensity was much flatter in the steady state than it was at 30 msec after the beginning of a step of light; this is attributed to a desensitization which develops with a delay of 50-100 msec.2. When a weak flash was superposed on a steady background light which hyperpolarized the cone by 3-6 mV the amplitude of the linear response to a flash was reduced to 1/e and the time to maximum was shortened from about 110 to 70 msec; the response also became diphasic. With stronger background lights the flash sensitivity continued to fall, but the time to maximum did not become shorter than 40-50 msec and lengthened again with very strong lights.3. In cones the flash sensitivity S(F) was reduced to half its dark value S(F) (D) by a light intensity of 1/S(F) (D)zeta where zeta is about 20 sec/V.4. At low levels of background light, about two-thirds of the change in sensitivity was time-dependent and one-third was attributable to the ;instantaneous non-linearity' described in the previous paper.5. The reduction in time to peak and the decrease in sensitivity produced by a background light which hyperpolarized by about 3 mV was little affected by changing the diameter of the area illuminated from 12 to 800 mum.6. An experiment with a rod showed that a very weak light which hyperpolarized by only 0.5 mV decreased the linear response to 1/e and shortened the time to maximum from 300 to 180 msec.7. With weak or moderate flashes the time-dependent desensitization lagged behind the potential by 50-100 msec.8. The desensitization and shortening of time scale which persisted after a flash or step were associated with an after-hyperpolarization. The relaxation of potential, sensitivity and time scale became slower as the preceding illumination was increased from 10(3) to 10(10) photons mum(-2); the increase seemed to occur in steps involving components which relaxed with time constants of the order of 0.1, 1, 10 and 100 sec. A rebound phenomenon was observed after steps longer than 30 sec and with equivalent intensities greater than 10(5) photons mum(-2) sec(-1).9. Several of the observations are explained by a hypothesis in which the central assumption is that the particles which block the ionic channels are degraded or removed by an autocatalytic reaction.

UI	MeSH Term	Description	Entries
D008027	Light	That portion of the electromagnetic spectrum in the visible, ultraviolet, and infrared range.	Light, Visible,Photoradiation,Radiation, Visible,Visible Radiation,Photoradiations,Radiations, Visible,Visible Light,Visible Radiations
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D008954	Models, Biological	Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.	Biological Model,Biological Models,Model, Biological,Models, Biologic,Biologic Model,Biologic Models,Model, Biologic
D010775	Photic Stimulation	Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity.	Stimulation, Photic,Visual Stimulation,Photic Stimulations,Stimulation, Visual,Stimulations, Photic,Stimulations, Visual,Visual Stimulations
D010786	Photoreceptor Cells	Specialized cells that detect and transduce light. They are classified into two types based on their light reception structure, the ciliary photoreceptors and the rhabdomeric photoreceptors with MICROVILLI. Ciliary photoreceptor cells use OPSINS that activate a PHOSPHODIESTERASE phosphodiesterase cascade. Rhabdomeric photoreceptor cells use opsins that activate a PHOSPHOLIPASE C cascade.	Ciliary Photoreceptor Cells,Ciliary Photoreceptors,Rhabdomeric Photoreceptor Cells,Rhabdomeric Photoreceptors,Cell, Ciliary Photoreceptor,Cell, Photoreceptor,Cell, Rhabdomeric Photoreceptor,Cells, Ciliary Photoreceptor,Cells, Photoreceptor,Cells, Rhabdomeric Photoreceptor,Ciliary Photoreceptor,Ciliary Photoreceptor Cell,Photoreceptor Cell,Photoreceptor Cell, Ciliary,Photoreceptor Cell, Rhabdomeric,Photoreceptor Cells, Ciliary,Photoreceptor Cells, Rhabdomeric,Photoreceptor, Ciliary,Photoreceptor, Rhabdomeric,Photoreceptors, Ciliary,Photoreceptors, Rhabdomeric,Rhabdomeric Photoreceptor,Rhabdomeric Photoreceptor Cell
D003116	Color	The visually perceived property of objects created by absorption or reflection of specific wavelengths of light.	Colors
D003624	Darkness	The absence of light.	Darknesses
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013696	Temperature	The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.	Temperatures
D013997	Time Factors	Elements of limited time intervals, contributing to particular results or situations.	Time Series,Factor, Time,Time Factor