An endogenous elevation of cGMP increases the excitability of identified insect neurosecretory cells |
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Authors: | Stephen C Gammie James W Truman |
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Institution: | (1) Zoology Department, Box 351800, University of Washington, Seattle, WA 98195-1800, USA, Tel.: +1-206/543-6513, Fax: +1-206/543-3041, e-mail: gammies@zoology.washington.edu, US |
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Abstract: | In the moth, Manduca sexta, the neuropeptide, eclosion hormone, triggers a dramatic rise in the levels of intracellular cGMP within a group of 50 neurons.
The cells within this group include the segmentally repeated neurosecretory cell, Cell 27. In this study the effect of cGMP
on the excitability of Cell 27 was investigated using intracellular recordings. Prior to its normal elevation in cGMP, Cell
27 exhibited a high spike threshold, but this was lowered dramatically when intracellular cGMP levels increased. The latter
was also associated with spontaneous action potentials. This change in excitability did not correspond with changes in either
resting potential, input resistance, or action potential amplitude. A similar lowering of threshold was induced by perfusion
of 8-bromo-cGMP, whereas 8-bromo-cAMP caused the threshold to increase. Intracellular recordings using various ion substitution
paradigms and channel blockers provided evidence which suggests indirectly that Ca2+ is mostly responsible for the depolarizing phase of the action potential while a Ca2+-activated K+ current contributes to the hyperpolarization. The results of these manipulations are consistent with the hypothesis that
cGMP may partially increase excitability in Cell 27 by enhancing an inward Ca2+ current.
Accepted: 31 October 1996 |
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Keywords: | Key words Manduca sexta Eclosion hormone CCAP Neurosecretory cGMP |
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