J. Okada et al., CHOLINERGIC INHIBITORY INNERVATION OF THE CARDIOARTERIAL VALVES IN THE ISOPOD BATHYNOMUS-DOEDERLEINI, Zoological science, 14(4), 1997, pp. 571-579
In the isopod Bathynomus doederleini, the cardioarterial valves of all
five pairs of lateral arteries and the pair of anterior lateral arter
ies are innervated by inhibitory (dilator) nerves which consist of one
or two axons arising from the central nervous system. Stimulation of
the valve dilator nerves produced inhibitory junctional potentials (IJ
Ps) in valve muscle cells which arose one-to-one in response to stimul
us pulses. Acetylcholine (ACh) hyperpolarized muscle cells of the valv
es. Both the IJPs and ACh-induced hyperpolarization brought about an i
ncrease of haemolymph pressure in the arteries, through relaxation of
valve muscles. The muscarinic agonists, muscarine, carbamylcholine and
arecoline, mimicked ACh-induced hyperpolarizing responses of the valv
e muscle cells. Atropine and methylxylocholine antagonized both the IJ
Ps and ACh-induced hyperpolarizing potentials, while d-tubocurarine di
d not antagonize IJPs. These results indicate that ACh may be the tran
smitter for the valve dilator nerves. IJPs did not invert in Cl--free
saline. Amplitude of IJPs increased in low K+ salines, and decreased i
n high K+ salines. It is likely that IJPs are mediated predominantly b
y K+ ions. This could be the first case of cholinergic inhibitory tran
smission at neuromuscular junctions in crustaceans.