Journal of Neuroscience, Vol 8, 4394-4399, Copyright © 1988 by Society for Neuroscience
Insect cardioactive neuropeptides: peptidergic modulation of the intrinsic rhythm of an insect heart is mediated by inositol 1,4,5- trisphosphate
NJ Tublitz
Institute of Neuroscience, University of Oregon, Eugene 97403.
The beat frequency of the myogenic heart of the tobacco hawkmoth, Manduca
sexta, markedly increases at adult emergence in response to 2 blood-borne
peptide neurohormones, known as the cardioacceleratory peptides (CAP1 and
CAP2). Three independent lines of evidence are presented supporting the
hypothesis that the CAPs exert their cardiostimulatory effects on the
insect myocardium through a change in the intracellular levels of inositol
1,4,5-trisphosphate (InsP3). I show that (1) InsP3 levels increase in
response to CAP2 in a timely fashion, (2) exogenous application of InsP3
mimics the effects of CAP2 application, and (3) a blocker of InsP3
metabolism inhibits the effect of CAP2. These results provide strong
support for the hypothesis that InsP3 is likely to be the second messenger
in the regulation of heart beat activity by CAP2. Besides establishing the
nature of the signaling system between CAP2 and the heart, these data also
identify a novel role for InsP3, namely, the control of contraction
frequency in a myogenic muscle. Given the widespread distribution of
cellular systems employing InsP3 as a second messenger, it is suggested
that InsP3 may also be involved in the long-term regulation of rhythmic
activity in other spontaneously contractile muscles and endogenously active
cells.