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1. The exponential decline of light-sensitive current seen after switch from Na+ to Li+ in the presence of Ca2+ probably depends on the activity of the phosphodiesterase (PDE) which hydrolyses cyclic GMP. 2. This probability is supported by experiments with suction electrodes which show that in toad and salamander rods the rate constant, b, of the(More)
1. In response to strong, large-field flashes the dark-adapted rods of Chelydra serpentina gave initial hyperpolarizing responses of 30-40 mV, declining rapidly to plateaus of 10-15 mV which lasted 20 sec or more.2. In the most sensitive cells the flash-sensitivity at 520 nm to a large illuminated area was 3-6 mV per photoisomerization (assuming an(More)
A new method is described for determining the effects of rapid changes in ionic concentration on the light-sensitive currents of rod outer segments. Replacing Na with another monovalent cation caused a rapid change in current followed by an exponential decline of time constant 0.5-2 s. From the magnitude of the initial rapid change in current we conclude(More)
1. Methods employing suction electrodes to measure the small inward currents associated with the exchange of internal Ca2+ for external Na+ in salamander rod outer segments are described. 2. The ratio of the integral of the exchange current to the integral of the Ca2+ current during the loading period averaged 0.37, which is consistent with 1 Ca2+ ion(More)
1. The electrical coupling between cones of known spectral sensitivity in the peripheral part of the turtle's retina was studied by passing current through a micro-electrode inserted into one cone and recording with a second micro-electrode inserted into a neighbouring cone. 2. Spatial sensitivity profiles were determined by recording flash responses to a(More)
The effect of ions on the light-sensitive current of retinal rods was studied by sucking the inner segment into a tightly fitting capillary with the outer segment projecting into a flowing solution. This new method showed that the light-sensitive pathway, in which Na+ is the normal carrier of current, has an ionic selectivity different from that of other(More)
The effect of ions on the light-sensitive current of isolated retinal rods from the toad Bufo marinus was studied by sucking the inner segment into a tightly fitting pipette. The outer segment projected into flowing solution whose composition could be changed rapidly. Reducing the external Na concentration, [Na]o, round the outer segment caused rapid and(More)
Flashing a localised stimulus onto a turtle's retina produces an intracellular potential wave which spreads through electrical connections from illuminated to unilluminated photoreceptors. The response in unilluminated rods (but not in cones) becomes faster as the distance from the source increases, perhaps because voltage-dependent permeability changes in(More)