Lysosome destabilization by cytosolic extracts, putative involvement of Ca(2+)/phospholipase C.

Lysosomal disintegration is a crucial event for living cells, but mechanisms for the event are still unclear. In this study, we established that the cytosolic extracts could enhance lysosomal osmotic sensitivity and osmotically destabilize the lysosomes. The cytosol also caused the lysosomes to become more swollen in the hypotonic sucrose medium. The results indicate that the cytosol induced an osmotic shock to the lysosomes and an influx of water into the organelle. Since the effects of cytosol on the lysosomes could be abolished by O-tricyclo[5.2.1.0(2,6)]dec-9-yl dithiocarbonate potassium salt (D609), a specific inhibitor of cytosolic phospholipase C (PLC), the PLC might play an important role in the lysosomal osmotic destabilization. The activity of cytosolic PLC and the extent of enzyme latency loss of the cytosol-treated lysosomes exhibited a similar biphasic dependence on the cytosolic Ca2+ concentration. In addition, the cytosol did not osmotically destabilize the lysosomes until the cytosolic calcium ions rose above 100 nM. It suggests that the destabilization effect of cytosol on the lysosomes is Ca(2+)-dependent.