In primate goblet cells, the membranes of adjacent mucous granules from contact areas which appear as extensive pentalaminar fusion sites in thin sections. In freeze-fracture replicas, the same membrane areas are smooth, except for a few 6-8-nm particles which adhere to the E face. These protein-poor membrane interaction sites are relatively long-lived, and it is proposed that further stimulus may be required to trigger membrane fission.

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