Multiple drug classes and hyperosmolarity alter binding of muscarinic drugs to mesothelial cells in vitro.

Mesothelial cells in vitro exhibited binding sites for L-quinuclidinyl[phenyl-4-3H]-benzilate ([3H]-QNB), but not [3H]-N-methylscopolamine (NMS), a cell-impermeable ligand. [3H]-QNB binding demonstrated a biphasic pattern of binding in living cells: a maximum after 15 min at 37 degrees C was followed by a decrease out to 90 min. [3H]-QNB binding was blocked by increasing concentrations of atropine; WIN35428 and GBR12909, dopamine transport inhibitors also decreased binding. Pretreatment of cells for 18 hours with atropine, QNB, or WIN35428 resulted in enhanced [3H]-QNB binding, but coexposure to cycloheximide blocked this increase. Hyperosmolarity caused by NaCl or mannitol decreased binding of [3H]-QNB to living cells. Thus rabbit peritoneal mesothelial cells possess binding sites for [3H]-QNB that are influenced by other drugs and osmolarity.