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)