Phosphatidylinositol‐specific phospholipase C solubilized G₂ acetylcholinesterase from plasma membranes of chromaffin cells

Abstract

Using whole homogenates and defined subcellular fractions of bovine adrenal medulla, we investigated the properties of the dimeric G2 molecular form of acetylcholinesterase (AChE), its distribution, and the mode of attachment to chromaffin cells. Our studies indicate that a substantial fraction of the G2 form is specifically susceptible to solubilization by phosphatidylinositol-specific phospholipase C (PIPLC) from subcellular fractions enriched with plasma membrane fragments. The results suggest that the G2 form of AChE is anchored in the plasma membrane to a glycolipid domain that contains phosphatidylinositol. Since a Ca+2-dependent PIPLC has been previously described in chromaffin granules, it is possible that the adrenal AChE could be released by a system reminiscent of that involved in the case of the surface glycoprotein of Trypanosoma brucei.

Expression of dimeric and tetrameric acetylcholinesterase isoforms on the surface of cultured bovine adrenal chromaffin cells

“…In this study, we examined the expression and cell-surface targeting of AChE isoforms using isolated adrenal medullary chromaffin cells in culture. Chromaffin cells are of neural crest origin and are known to express both soluble and membrane-bound forms of AChE [Mizobe and Iwamoto, 1983;Mizobe and Livett, 1983;Mizobe et al, 1984;Prieto et al, 1989;Bon et al, 19901. AChE is actively secreted by chromaffin cells [Mizobe and Livett, 19801.…”

Association of Acetylcholinesterase with the cell surface

“…This group of surface proteins includes alkaline phosphatase, 5'-nucleotidase, Thy-1, a 120-kDa neural cell adhesion molecule (N-CAM120), the scrapie prion protein (Pr P27-30) and the variant surface glycoprotein (VSG) of Trypanosoma brucei (Low, 1989). The amphiphilic dimeric AChE was shown to be solubilized from various sources such as rat and bovine erythrocytes, tegument of the worm Schistosoma mansoni, Torpedo electric organ, Xenopus skeletal muscle, rat liver, bovine chromaffin cells and human heart (Futerman et al, 1985b;Espinoza et al, 1988;Inestrosa et al, 1988;Perelman & Brandan, 1989;Prieto et al, 1989;Gonz~ilez et al, 1990). The enzymes were released in a soluble nonaggregating hydrophilic form.…”

“…Recently, we studied in detail AChE forms found in hepatocytes and adrenal medulla cells (Perelman & Brandan, 1989;Prieto et al, 1989). In rat hepatocytes, ,81% of the AChE activity was localized in the hepatocyte surface facing the extracellular media.…”