RETINOIC ACID-INDUCED DIFFERENTIATION OF A HUMAN NEUROBLASTOMA CELL-LINE ALTERS MUSCARIC RECEPTOR EXPRESSION

Muscarinic receptor density increased by approximately 36% after differentiation induced by retinoic acid (B(max), control = 126 +/- 13 fmol/mg protein; B(max), retinoic acid-treated = 170 +/- 17 fmol/mg protein; P < 0.05), corresponding to a 170% increase in receptor content per cell. The affinity of [H-3]NMS for the receptors was somewhat lower in the retinoic acid-treated cells (K(d), control = 0.14 +/- 0.04 nM; K(d), retinoic acid-treated = 0.25 +/- 0.04 nM; P < 0.05). Reverse transcriptase/polymerase chain reaction analysis using subtype-specific primers revealed that undifferentiated Sk-N-SH cells transcribed mRNA for all 5 receptor subtypes; this pattern was not affected by retinoic acid treatment. [H-3]NMS displacement curves with subtype selective receptor ligands (pirenzepine, ml; AFDX-116, m2; 4-DAMP, m3) indicated the predominant expression of m3 and ml receptor subtypes, and differentiation did not affect the pharmacological profile of the expressed receptor populations. The present results indicate that differentiation induces selective changes in the expression and activity of muscarinic receptors in a neuronal cell line.