Influence of cumulus cell processes on oolemma permeability and lethality of isolated mouse oocytes cultured in Ca2+-free medium

Cumulus cell processes remaining in the zona pellucida of mouse occytes mechanically isolated from the ovary have been indirectly visualized by labeling their actin microfilament core with rhodaminyl-phalloidin. If the isolation of the oocytes is performed in Ca²⁺-free medium, the preisence of such processes allows the entry into the cell of low molecular weight molecules (such as 5-6 carboxyfluorescein) and contributes to the death of the cell in such experimental conditions. Following dissolution of the zona pellucida (by enzymatic or acidic treatment) the oocyte is no longer permeable to small molecules and becomes resistant to Ca²⁺-free medium, probably as a consequence of the collapse of cumulus cell processes. The role of cumulus cell processes and gap junctions in the permeability of mechanically isolated ovarian oocytes is discussed.