The human astrocytoma cell line 1321 N1 contains M2-glandular type muscarinic receptors linked to phosphoinositide turnover.

1. Muscarinic receptors present in the human astrocytoma cell line 1321 N1 were characterized in radioligand binding studies and in functional studies of carbachol-stimulated phosphatidylinositol (PI) turnover. 2. In radioligand binding studies the muscarinic receptor in intact cells could be labelled using [3H]-N-methylscopolamine ([3H]-NMS) but not by [3H]-pirenzepine. In the intact cells these receptors displayed low pirenzepine affinity (pKi = 6.83) indicating that they were not of the M1 subtype. Furthermore, the 1321 N1 muscarinic receptors displayed low affinity for the two M2-cardiac selective ligands methoctramine (pKi = 5.82) and AF-DX 116 (pKi = 6.29). This pharmacology was consistent with the 1321 N1 cells containing a single population of muscarinic receptors that displayed a similar pharmacology to the M2-receptor present in exocrine gland tissue. 3. The M2-gland nature of the receptors was further indicated in the functional studies where antagonist affinities were determined from their ability to antagonize carbachol-stimulated PI turnover in 1321 N1 cells. pA2 values for pirenzepine (7.31), methoctramine (6.10) and AF-DX 116 (6.52) were similar to those determined in the binding studies. 4. From these studies we conclude that 1321 N1 astrocytoma cells contain an M2-gland muscarinic receptor which mediates muscarinic receptor-mediated stimulation of PI turnover in these cells.