A possible structural basis for the extracellular release of acetylcholinesterase

Abstract

The ultrastructural localization of acetylcholinesterase and non-specific cholinesterase activity has been studied in sections of ox adrenal medulla by cytochemical methods. Non-specific cholinesterase activity, identified by using butyrylthiocholine as substrate and ethopropazine as inhibitor, occurs intracellularly in some adrenaline-containing chromaffin cells: the reaction end-product is deposited within the cisternae of the endoplasmic reticulum and in the nuclear envelope. Reaction end-product of non-specific cholinesterase also occurs in the endoplasmic reticulum of pericytes, around sinusoids and capillaries and within smooth muscle cells. Acetylcholinesterase activity, identified by using acetylthiocholine as substrate and BW 284C51 as inhibitor, occurs in both the splanchnic nerve and in chromaffin cells. Reaction end-product is found at the following sites (i) around myelinated and unmyelinated non-terminal axons of splanchnic nerve, between the axolemma and the Schwann cell membrane; (ii) within the cisternae of axonal smooth endoplasmic reticulum; sometimes these cisternae appear to be connected to the axolemma; (iii) between the axolemmas of preterminal axons and the plasma membranes of chromaffin cells; (iv) between the axolemmas of nerve terminals and the plasma membranes of chromaffin cells, including the synaptic cleft; (v) within cisternae of rough and smooth endoplasmic reticulum, and also within the nuclear envelope, of both adrenaline- and noradrenaline-containing chromaffin cells; (vi) between the plasma membranes of adjacent chromaffin cells, but only when one or both of these cells contain reaction product within the cisternae of its endoplasmic reticulum; these cisternae sometimes appear to be connected to the plasma membrane. These observations raise the question whether the acetylcholinesterase activity released from the perfused adrenal gland might originate from the cisternae of the endoplasmic reticula of splanchnic nerve and/or chromaffin cell.