Physiological characteristics of single green rod photoreceptors from toad retina.
AUTOR(ES)
Matthews, G
RESUMO
The outer segment membrane current of single isolated green and red rods from toad retina was recorded with a suction electrode, and characteristics of the response to light were examined. The maximum response amplitude of green rods was smaller than that of red rods, but the density of dark current along the green rod outer segment was similar to previously reported values for red rods. Thus, the smaller maximum response is explained by the shorter outer segment of green rods (45 vs. 60 microns). The intensity-response relation was fitted by a Michaelis equation with half-saturating photon density corresponding to about 55 isomerizations per flash. The form of the green rod light response was similar to that of red rods: in both cases the kinetics were consistent with four first-order delay stages shaping the light response. The time-to-peak of the dim-flash response was usually about 1 sec for both green and red rods in the present experiments. The spectral sensitivity curve of green rods was fitted by the nomogram for a vitamin A1-based pigment with lambda max = 433 nm. The relation between steady light intensity and flash sensitivity of green rods obeyed the Weber-Fechner relation, and the average background intensity necessary to reduce sensitivity to half of its dark level corresponded to about 4 isomerizations sec-1. This is slightly lower than the value of about 8 isomerizations sec-1 reported for toad red rods by Baylor, Matthews & Yau (1980). Green rods were similar to red rods in all respects except spectral sensitivity. Thus, no evidence was found to support the assertion that green rods are 'cone-like'.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1193963Documentos Relacionados
- Dark noise in the outer segment membrane current of green rod photoreceptors from toad retina.
- Responses to light of solitary rod photoreceptors isolated from tiger salamander retina.
- The absence of spread of adaptation between rod photoreceptors in turtle retina.
- An alternative pathway for signal flow from rod photoreceptors to ganglion cells in mammalian retina.
- Evidence for the identification of synaptic transmitters released by photoreceptors of the toad retina.