Transient interactions between collagen-tailed acetylcholinesterase and sulfated proteoglycans prior to immobilization on the extracellular matrix.

Heparin is capable of solubilizing a subset of collagen-tailed (A12) acetylcholinesterase (AChE) molecules from skeletal basal lamina (Rossi, S. G., and Rotundo, R. L. (1993) J. Biol. Chem. 268, 19152-19159). In the present study, we used tissue-cultured quail myotubes to show that, like adult fibers, neither heparin- nor high salt-containing buffers detached AChE molecules from cell-surface clusters. Prelabeling clustered AChE molecules with anti-AchE monoclonal antibody 1A2 followed by incubation in heparin-containing medium showed that there was no reduction in the number or size of preexisting AChE clusters. In contrast, incubation of myotubes with culture medium containing heparin for up to 4 days reversibly blocked the accumulation of new cell-surface AChE molecules without affecting the rate of AChE synthesis or assembly. Newly synthesized A12 AChE becomes tightly attached to the extracellular matrix following externalization. However, in the presence of heparin, blocking the initial interactions between A12 AChE and the extracellular matrix results in release of AChE into the medium with a t1/2 of approximately 3 h. Together, these results suggest that once A12 AChE is localized on the cell surface, initially attached via electrostatic interactions, additional factors or events are responsible for its selective and more permanent retention on the basal lamina.