A role for adenosine in metabolic depression in the marine
invertebrate sipunculus nudus.
Reipschl[umlaut]ager, Anke, G[diaeresis]oran E. Nilsson, and Hans O.
P[diaeresis]ortner.
Alfred-Wegener-Institut f[umlaut]ur Polar- und Meeresforschung,
Biologie I/[diaeresis]okophysiologie, Postfach 120161, D-27515
Bremerhaven, F.R.G.; Vertebrate Physiology and Behaviour Unit,
Department of Limnology, Uppsala University, Norbyvagen 20, S-75236
Uppsala, Sweden; and Division of General Physiology, University of
Oslo, P.O. Box 1051, N-0316 Oslo, Norway
APStracts 3:0272R, 1996.
The involvement of neurotransmitters in metabolic depression was
examined in Sipunculus nudus. Metabolic depression in this species
occurs under both hypoxia and hypercapnia. Concentration changes of
several putative neurotransmitters in the nervous tissue observed
during anoxic or hypercapnic exposure or during combined anoxia and
hypercapnia were evaluated with respect to their possible
contribution to metabolic depression. Among amino acids (GABA,
glutamate, glycine, taurine, serine and aspartate) and monoamines
(serotonin, dopamine and norepinephrine) some changes were
significant but none were consistent with metabolic depression under
all experimental conditions applied. Only the neuromodulator
adenosine displayed concentration changes in accordance with
metabolic depression under all experimental conditions. Levels
increased during anoxia, during hypercapnia and to an even higher
extent during anoxic hypercapnia. Adenosine infusions into the
coelomic fluid via an indwelling catheter induced a significant
depression of the normocapnic rate of oxygen consumption from 0.36+/
-0.04 to a minimum value of 0.24+/-0.02 [mu]mol x g-1 x h-1 after 90
min (means+/-SE, n=6). Application of the adenosine antagonist
theophylline caused a transient rise in oxygen consumption 30 min
after infusion during hypercapnia but not during normocapnia. The
effects of adenosine and theophylline were observed in intact
individuals but not in isolated body wall musculature. The results
provide evidence for a role of adenosine in inducing metabolic
depression in S. nudus, probably through the established effects of
decreasing neuronal excitability and neurotransmitter release.
Considering our previous finding of metabolic depression in isolated
body wall musculature being elicited by extracellular acidosis
(Reipschl[umlaut]ager and P[diaeresis]ortner, 1996), it is concluded
that central and cellular mechanisms combine to contribute to the
overall reduction in metabolic rate in S. nudus.
Received 19 March 1996; accepted in final form 25 June 1996.
APS Manuscript Number R171-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996