M. Quik et al., ALPHA-BUNGAROTOXIN BLOCKS THE NICOTINIC RECEPTOR-MEDIATED INCREASE INCELL NUMBER IN A NEUROENDOCRINE CELL-LINE, Brain research, 655(1-2), 1994, pp. 161-167
Exposure of H69 small cell lung carcinoma cells to nicotinic agonists
resulted in a significant increase (up to 100%) in cell number after 6
to 12 days. The effect of nicotine (10(-8) M to 10(-4) M) was both do
se and time dependent as was that of another nicotinic agonist cytisin
e (10(-6) M to 10(-4) M). Interestingly, both the nicotine and cytisin
e induced increases in H69 cell number were blocked by alpha-bungaroto
xin, as well as d-tubocurarine a nicotinic blocker which appears to in
teract with most nicotinic receptors. These results suggest that the n
icotine induced increase in cell number is mediated through an interac
tion at the nicotinic alpha-bungarotoxin receptor. This idea is furthe
r supported by experiments which show (1) that H69 cells possess high
affinity alpha-bungarotoxin sites (K-d = 25 nM, B-max = 10.4 fmol/10(6
) cells) with the characteristics of a nicotinic alpha-bungarotoxin re
ceptor and (2) that the potencies of nicotinic receptor ligands in the
alpha-bungarotoxin binding assay were similar to those observed in th
e functional studies. Northern analysis showed that mRNA for alpha 7,
a putative nicotinic alpha-bungarotoxin binding subunit, and for alpha
5 were present in H69 cells. The present data provide further evidenc
e that nicotine increases cell number in small cell lung carcinoma and
are the first to show that this effect is mediated through an interac
tion at the nicotinic alpha-bungarotoxin receptor population. These re
sults suggest that the alpha-bungarotoxin site may be involved in modu
lating proliferative responses in neuroendocrine derived SCLC cells.