PT  - JOURNAL ARTICLE
AU  - Smith, KE
AU  - Kessler, JA
TI  - Non-neuronal cell-conditioned medium regulates muscarinic receptor expression in cultured sympathetic neurons
AID  - 10.1523/JNEUROSCI.08-07-02406.1988
DP  - 1988 Jul 01
TA  - The Journal of Neuroscience
PG  - 2406--2413
VI  - 8
IP  - 7
4099  - http://www.jneurosci.org/content/8/7/2406.short
4100  - http://www.jneurosci.org/content/8/7/2406.full
SO  - J. Neurosci.1988 Jul 01; 8
AB  - Regulation of muscarinic receptor expression was examined in cultured sympathetic neurons of the neonatal rat superior cervical ganglion. Receptor concentration was determined by measuring binding of the muscarinic antagonist 1-quinuclidinyl[phenyl-4-3H] benzilate (3H-QNB). 3H-QNB bound to one apparent class of noninteracting sites on sympathetic neuron membranes with a Kd of 28.9 pM and a Bmax of 2.91 pmol/mg protein. Binding increased as a linear function of tissue protein and was saturable. The number of receptors per milligram protein increased approximately 6-fold during 16 d of culture, and receptor numbers were down-regulated by treatment with the agonist carbachol. These observations suggested that measurement of 3H-QNB binding would provide a reliable estimate of muscarinic receptor number on cultured sympathetic neurons. To determine whether nonneuronal cells produce soluble factors that influence muscarinic receptor expression, the effects of treatment with rat fibroblast-conditioned medium (RFCM) were examined. Exposure of sympathetic neurons to 50% RFCM resulted in a 57% decrease in muscarinic receptor numbers without a change in the apparent Kd. The decrease in 3H-QNB binding in response to RFCM was dose-related, with a minimum dose of 15% RFCM required to observe a significant effect. In contrast to the carbachol-induced down- regulation, the reduction in binding after RFCM treatment was not prevented by atropine, indicating that the effect was not mediated by acetylcholine stimulation of muscarinic receptors. Binding of 125I- alpha-bungarotoxin, which labels a nonfunctional membrane site distinct from nicotinic receptors, was not altered by treatment with RFCM, indicating the selectivity of the change in membrane muscarinic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)