Journal of Applied Physiology, Vol 66, Issue 5 2084-2091, Copyright © 1989 by American Physiological Society
Adenosine selectively inhibits noncholinergic transmission in guinea pig bronchi
Y. Kamikawa and Y. Shimo
Department of Pharmacology, Dokkyo University School of Medicine, Tochigi, Japan.
The neuromodulatory action of adenosine and ATP was investigated in
isolated guinea pig bronchial strip chain preparations contracted with
electrical field stimulation. The tissues were placed in organ baths
containing physiological salt solution and stimulated at 8-Hz frequency,
0.5-ms pulse duration, and 30 V (approximately 100 mA) for 5 s. Electrical
field stimulation evoked a biphasic contraction of bronchial muscle,
consisting of an initial contraction followed by a sustained contraction,
which was mediated by intramural cholinergic and noncholinergic nerve
stimulations, respectively. Adenosine, at concentrations greater than M,
caused a concentration-dependent inhibition in the height of the
noncholinergically mediated contraction, accompanied by a very weak
inhibition on the cholinergically mediated response. ATP (10(-5) to 3 x
10(-3) M) also produced a similar inhibitory effect on the
noncholinergically mediated contraction, but the inhibitory potency was
less than that of adenosine. The inhibitory response to adenosine was
enhanced by the pretreatment with dipyridamole (2 x 10(-6) M) but
antagonized with aminophylline (10(-5) M). Contractions of bronchial muscle
evoked by exogenous acetylcholine (2 x 10(-6) M) or substance P (2 x 10(-7)
M) were significantly inhibited by the adenosine (3 x 10(-4) M)
pretreatment. These data suggest that in isolated guinea pig bronchi
adenosine selectively inhibits noncholinergic neurotransmission through
prejunctional P1-purinoceptors.
