Biomaterial Database

The electrical response of turtle cones to flashes and steps of light. 1974

D A Baylor, and A L Hodgkin, and T D Lamb

1. The linear response of turtle cones to weak flashes or steps of light was usually well fitted by equations based on a chain of six or seven reactions with time constants varying over about a 6-fold range.2. The temperature coefficient (Q(10)) of the reciprocal of the time to peak of the response to a flash was 1.8 (15-25 degrees C), corresponding to an activation energy of 10 kcal/mole.3. Electrical measurements with one internal electrode and a balancing circuit gave the following results on red-sensitive cones of high resistance: resistance across cell surface in dark 50-170 MOmega; time constant in dark 4-6.5 msec. The effect of a bright light was to increase the resistance and time constant by 10-30%.4. If the cell time constant, resting potential and maximum hyperpolarization are known, the fraction of ionic channels blocked by light at any instant can be calculated from the hyperpolarization and its rate of change. At times less than 50 msec the shape of this relation is consistent with the idea that the concentration of a blocking molecule which varies linearly with light intensity is in equilibrium with the fraction of ionic channels blocked.5. The rising phase of the response to flashes and steps of light covering a 10(5)-fold range of intensities is well fitted by a theory in which the essential assumptions are that (i) light starts a linear chain of reactions leading to the production of a substance which blocks ionic channels in the outer segment, (ii) an equilibrium between the blocking molecules and unblocked channels is established rapidly, and (iii) the electrical properties of the cell can be represented by a simple circuit with a time constant in the dark of about 6 msec.6. Deviations from the simple theory which occur after 50 msec are attributed partly to a time-dependent desensitization mechanism and partly to a change in saturation potential resulting from a voltage-dependent change in conductance.7. The existence of several components in the relaxation of the potential to its resting level can be explained by supposing that the ;substance' which blocks light sensitive ionic channels is inactivated in a series of steps.

UI	MeSH Term	Description	Entries
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
D008839	Microelectrodes	Electrodes with an extremely small tip, used in a voltage clamp or other apparatus to stimulate or record bioelectric potentials of single cells intracellularly or extracellularly. (Dorland, 28th ed)	Electrodes, Miniaturized,Electrode, Miniaturized,Microelectrode,Miniaturized Electrode,Miniaturized Electrodes
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
D004566	Electrodes	Electric conductors through which electric currents enter or leave a medium, whether it be an electrolytic solution, solid, molten mass, gas, or vacuum.	Anode,Anode Materials,Cathode,Cathode Materials,Anode Material,Anodes,Cathode Material,Cathodes,Electrode,Material, Anode,Material, Cathode
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