476 BIOCHEMISTRY OF DEVELOPMENT AND DIFFERENTIATION I (1298-1303)

1298 BIOCHEMISTRY
REGULATION OF CALCIUM UPTAKE IN NEUROBLASTOMA OR HYBRID
CELLS - A POSSIBLE MECHANISM FOR SYNAPSE PLASTICITY.
A. Rotter®, R. Ray* and M. Nirenberg. NIH, Bethesda, Md. 20014
Thirteen neuroblastoma or hybrid cell lines with or with
out defects in stimulus-dependent acetylcholine release and
synapse formation (Wilson, S., et al. (1978) Fed. Proc. 37,
2819) were tested for Kt-dependent 45ca2+ uptake. NBrlOA
hybrid cells (synapset) grown for days with 1 mM dibutyryl
cAMP (Bt2cAMP) and incubated with 5.4 or 85.4 mM Kt accumu-
late 2.5 and 5.0 nmoles of 45ca2t+/5 min/mg protein, respec—
tively. Methoxy-verapamil inhibits Kt-dependent 45¢a2t
uptake >95% (1059 = 2x10-7 M) but has no effect on basal
45ca2+ uptake. Sca2+ uptake also is inhibited by 10 mM La3t,
Co2+, ni2t, Mn2+ or Sr2+ but not by 10 wM tetrodotoxin, 20 mM
tetraethylammonium or 1 mM 3,4-diaminopyridine. Logarith-
mically dividing NBr10A cells grown without Bt cAMP do not
respond to Kt by accumulating 5ca2+ put can be shifted to a
responsive state by treatment for 7 days with BtgcAMP or
10 pM PGE] (an activator of adenylate cyclase) and 1 mM
theophylline. Examination of 12 other cell lines grown with
BtgcAMP revealed 2 classes of synapse defects: (1) defects
in Kt-dependent 45ca2t uptake and (2) defects in another
unidentified step required for synapse formation. These
results show that the Ca + uptake is regulated and that cell
lines with or without defects in Ca + uptake can be generated.
The results suggest that cAMP is required for the acquisition
of xt-dependent Catt uptake thereby regulating synapse
formation and efficiency.

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