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

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 mum (mean +/ - S.D, n = 104) in length and 6.6 +/ - 0.9 mum (mea n +/ - 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, 20degreesC) 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 rod s 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 f rom 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 pA(2) (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)