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Fig. 2. Proctolin enhances the amplitude of high (30 mmol l-1)
K+-induced contractures of Idotea muscle fibres. (A)
Membrane potential (top) and tension (bottom) measured simultaneously before
application of proctolin (control), in the presence of 1 µmol
l-1 proctolin, and after washing off proctolin for 30 min. Control
shows one of three K+-contractures prior to the peptide tests. (B)
Normalised membrane potentials and tensions (N=8) of the experiments
as shown in A, indicating no significant change in membrane potential (top)
and a 47% increase in the amplitudes of K+-contractures with the
peptide (bottom). (C) K+-induced contractures measured before
exposure to proctolin (control), after a 5 min application of 1 µmol
l-1 proctolin in the presence of the PKA inhibitor H89 (1 µmol
l-1) for 5 min, and after washing off proctolin and H89 for 30 min.
(D) Summary of independent experiments showing the maximal amplitude of
contractures normalised to the controls. 1 µmol l-1 proctolin
increases the amplitudes of contractures significantly (N=8). In the
presence of 20 µmol l-1 H89, proctolin increases the amplitudes
of contractures significantly compared to controls without H89 (N=4).
H89 alone significantly increases the amplitudes of contractures
(N=6). *P<0.05.
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