ACTIVATION OF NICOTINIC RECEPTOR-INDUCED POSTSYNAPTIC RESPONSES TO LUTEINIZING-HORMONE-RELEASING HORMONE IN BULLFROG SYMPATHETIC-GANGLIA VIA A NA-DEPENDENT MECHANISM()
Yj. Cao et Yy. Peng, ACTIVATION OF NICOTINIC RECEPTOR-INDUCED POSTSYNAPTIC RESPONSES TO LUTEINIZING-HORMONE-RELEASING HORMONE IN BULLFROG SYMPATHETIC-GANGLIA VIA A NA-DEPENDENT MECHANISM(), Proceedings of the National Academy of Sciences of the United Statesof America, 95(21), 1998, pp. 12689-12694
Nicotine at very low doses (5-30 nM) induced large amounts of luteiniz
ing hormone-releasing hormone (LHRH) release, which was monitored as s
low membrane depolarizations in the ganglionic neurons of bullfrog sym
pathetic ganglia, A nicotinic antagonist, d-tubocurarine chloride, com
pletely and reversibly blocked the nicotine-induced LHRH release, but
it did not block the nerve-firing-evoked LHRH release. Thus, nicotine
activated nicotinic acetylcholine receptors and produced LHRH release
via a mechanism that is different from the mechanism for evoked releas
e. Moreover, this release was not caused by Ca2+ influx through either
the nicotinic receptors or the voltage-gated Ca2+ channels because th
e release was increased moderately when the extracellular solution was
changed into a Ca2+-free solution that also contained Mg2+ (4 mM) and
Cd2+ (200 mu M). The release did not depend on Ca2+ release from the
intraterminal Ca2+ stores either because fura-2 fluorimetry showed ext
remely low Ca2+ elevation ( approximate to 30 nM) in response to nicot
ine (30 nM), Moreover, nicotine evoked LHRH release when [Ca2+] elevat
ion in the terminals was prevented by loading the terminals with 1,2-b
is (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid and fura-2, Inst
ead, the nicotine induced release required extracellular Na+ because s
ubstitution of extracellular NaCl with N-methyl-D-glucamine chloride c
ompletely blocked the release. The Na+-dependent mechanism was not via
Na+ influx through the voltage-gated Na+ channels because the release
was not affected by tetrodotoxin (1-50 mu M) plus Cd2+ (200 mu M). Th
us, nicotine at very low concentrations induced LHRH release via a Na-dependent, Ca2+-independent mechanism.