Membrane current of retinal rods of Caudiverbera caudiverbera (Amphibia: Leptodactylidae): dark noise, spectral and absolute light sensitivity.
We investigated the photocurrents from isolated rods of the South American anuran, Caudiverbera caudiverbera. Rod outer segments were on average 66.4 +/- 11.2 microm (mean +/- S.D., n = 104) in length and 6.6 +/- 0.9 microm (mean +/- S.D.) in diameter: 40 +/- 22 photoisomerizations (mean +/- S.D., range 10-99, n = 16) were required for eliciting a half-saturating photocurrent response. The time-to-peak was 911 +/- 217 ms (mean +/- S.D., n = 14, 20 degrees C) in the linear range of the response and the integration time of the current response was 1744 +/- 451 ms (mean +/- S.D., n = 14). The time-to-peak appears to be slower and the integration time shorter in Caudiverbera than in Ambystoma tigrinum, Rana pipiens or Xenopus laevis rods under similar experimental conditions. The a-band of rod spectral sensitivity has a lambda(max) at 520 +/- 2.1 nm (mean +/- S.D., range 516-525 nm, n = 24) and the bandwidth fits a porphyropsin visual pigment. The single-event response amplitude ranges from 0.31-0.51 pA, depending on the calculation method. The intrinsic dark current (variance at dark minus variance under bright light) was 0.045 +/- 0.040 pA2 (mean +/- S.D., n = 24). Our results support the presence of a dark-noise component below 1 Hz, with kinetics similar to the single-photon evoked response and a rate of 0.006 events s(-1) (n = 9).
Palma
F
F
Department of Physiology, Faculty of Sciences, and Valparaíso Molecular and Cellular Center for Neuroscience, University of Valparaíso, Chile.
Roncagliolo
P
P
Bacigalupo
J
J
Palacios
A G
AG
D000663:Amphibians / Q000502:physiology*; D000818:Animals; D016477:Artifacts; D003624:Darkness; D004553:Electric Conductivity; D004594:Electrophysiology; D066298:In Vitro Techniques; D007700:Kinetics; D008027:Light; D008954:Models, Biological; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology* / Q000528:radiation effects; D014785:Vision, Ocular; D014982:Xenopus laevis / Q000502:physiology