80% of muscarinic receptors expressed by the NB-OK 1 human neuroblastoma cell line show high affinity for pirenzepine and are comparable to rat hippocampus M1 receptors.

The NB-OK 1 human neuroblastoma cell line expressed muscarinic cholinergic receptors that could be labeled with N-[3H]methylscopolamine (a nonselective antagonist). 80% of these receptors showed high affinity for pirenzepine, i.e. belonged to the M 1 subtype found in neuronal tissues. Their binding properties were identical to those of rat hippocampus M 1 receptors, and differed from those of rat pancreas and heart muscarinic receptors. The remaining (20%) muscarinic receptors showed low affinity for pirenzepine and AF-DX 116, being therefore of an M2 beta (or B) subtype, and were similar to rat pancreatic receptors.