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Fig. 8. Analysis of the amplitude reduction of action potentials (APs). (A) The
8bcGMP-dependent AP amplitude reduction for the beginning (i), the middle (ii)
and the end (iii) of one recording at ZT 8-11. Plots show the mean of the
positive amplitude of APs that occurred during an interval of 1 min before to
2 min after the stimulation. Arrows indicate the time of stimulation. Each
plot consists of the binned (binwidth=10 ms) and averaged AP amplitudes of
three consecutive responses to a stimulus of 10 µg BAL. For the first three
responses of the recording the AP amplitudes were strongly reduced. The APs
returned to its pre-stimulus amplitude not until about 2 min after the stimuli
were applied. After about 90 min the slow portion of the recovering phase
disappeared. Also, the amplitude reduction showed a slight decrease. At the
end of the recording a strong 8bcGMP-dependent decrease in the amplitude
reduction was observed. The amplitude reduction was only weak and transient.
In the control recordings no or only weak fluctuations in the reduction of
positive APs were found. In contrast to the recording with 8bcGMP the slowly
recovering phase is even more prominent at the end of the recording. (Due to
the non-linear change of the BAL-AP amplitude in the post-stimulus portion
BAL- and non-BAL APs could not be distinguished). (B) Normalized ratio between
the minimal and maximal positive AP amplitude of a response as a mean of the
strength of the amplitude reduction. Each recording was normalized to the
first value. Values >1 represent a decrease in the reduction of the AP
amplitude. In recordings from ZT 1-4 with 10 mmol l-1 8bcGMP
diluted in the sensillum lymph ringer (top right), two populations of
recordings can be observed. One population showed a very strong increase from
the beginning on, the other one resembled the time course of the reduction in
control recordings. For control recordings from ZT 1-4 (top left), most of the
data points showed a cumulative composition at the beginning followed by an
increasing variance leading to a continuous broadening in the distribution
later in the recordings. Under the influence of 8bcGMP all of the recordings
from ZT 8-11 (bottom right) showed an increase, whereas in the associated
controls (bottom left) most data points were located in a relatively distinct
band around 1.
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