these findings raise the possibility that the different pirenzepine binding characteristics used to define m1 and m2 receptor subtypes are not inherent in the receptor protein itself , but may be due to coupling factors such as effector proteins , phospholipids or cytoskeletal proteins which could be associated with the membranous receptor and become dissociated from the receptor after solubilization .
C0033684
proteins
C0010852
cytoskeletal proteins