Kf. Schmidt et al., CONFIGURATION OF LIGHT RESPONSES IN ISOLATED RETINAL RODS - A PATCH-CLAMP STUDY, Graefe's archive for clinical and experimental ophthalmology, 232(3), 1994, pp. 153-161
The whole-cell patch-clamp technique was employed to investigate the l
ight responses of single retinal rods of the frog (Rana esculenta and
R. temporaria). In the majority of experiments, completely isolated ce
lls were studied. Coupling with neighboring cells gave rise to a more
complex response configuration. Responses were recorded under voltage-
clamp and under current-clamp conditions. Stimulus response curves wer
e measured in experiments with local stimuli illuminating only parts o
f the outer segment. Metabolic factors such as cGMP, GTP and ATP were
also tested and were found to have specific and different influences o
n the response configurations. When the recording pipette was filled w
ith an intracellular medium devoid of nucleotides, a retardation in th
e recovery of the light responses was observed during the course of an
experiment. Addition of 1 mM ATP to the pipette medium prevented the
larger part of the retardation, while 1 mM GTP accelerated the respons
e recovery at the beginning of an experiment but did not prevent a sub
sequent retardation. Micromolar concentrations of cGMP were sufficient
to elicit both a depolarization of the photoreceptor membrane and an
increase in the response duration. These results show that, in single
photoreceptors, the configuration of light responses not only depends
on the stimulus parameters but also on those properties of the cells t
hat are directly controlled by their nucleotide metabolism.