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Membrane current of retinal rods of Caudiverbera caudiverbera (Amphibia: Leptodactylidae): Dark noise, spectral and absolute light sensitivity

Published online by Cambridge University Press:  11 January 2002

FRANCISCO PALMA
Affiliation:
Department of Physiology, Faculty of Sciences, and Valparaíso Molecular and Cellular Center for Neuroscience, University of Valparaíso, Valparaíso, Chile
PABLO RONCAGLIOLO
Affiliation:
Department of Physiology, Faculty of Sciences, and Valparaíso Molecular and Cellular Center for Neuroscience, University of Valparaíso, Valparaíso, Chile
JUAN BACIGALUPO
Affiliation:
Millennium Institute for Advanced Studies in Cell Biology and Biotechnology and Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile
ADRIÁN G. PALACIOS
Affiliation:
Department of Physiology, Faculty of Sciences, and Valparaíso Molecular and Cellular Center for Neuroscience, University of Valparaíso, Valparaíso, Chile

Abstract

We investigated the photocurrents from isolated rods of the South American anuran, Caudiverbera caudiverbera. Rod outer segments were on average 66.4 ± 11.2 μm (mean ± S.D., n = 104) in length and 6.6 ± 0.9 μm (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°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 α-band of rod spectral sensitivity has a λmax 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).

Type
Research Article
Copyright
2001 Cambridge University Press

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