Reduced pinosome formation in a cell‐fusion‐impaired mutant of mouse lymphocytic cell line L5178Y

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Abstract
Accumulation and release of a fluid‐phase marker ([14C]‐sucrose) were studied in a subline of the mouse lymphocytic cell line L5178Y and in a polyethylene glycol‐resistant, intercellular‐fusion‐impaired mutant of this line. The mutant was found to accumulate [14C]‐sucrose at a significantly slower rate than the parent. Analysis of release of preloaded label shows that the reduced rate of accumulation is due to a correspondingly low level of internalization, i.e., pinosome formation, rather than to a reduction in delivery of label to lysosomes. Cell‐to‐cell fusion and pinosome formation both involve a fusion event initiated at the extracellular surface of the plasma membrane, and we propose that the coordinate reduction in both processes suggests that they are mechanistically related.