Membrane permeability changes in amphibian eggs at ovulation

✍ Scribed by Gene A. Morrill; Jean Rosenthal; Donald E. Watson

• Book ID: 102881779
• Publisher: John Wiley and Sons
• Year: 1966
• Tongue: English
• Weight: 543 KB
• Volume: 67
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1040670303

✦ Synopsis

Electropotential differences between the cytoplasm and external medium have been compared in the mature R. pipiens occyte and the ovulated unfertilized egg as a function of [Na],, [K],, [Ca], and [Cl],. In solutions containing 1.0 mM Ca++ the oocyte behaved as though it were predominantly permeable to K + and C1-, i.e., like a KC1 electrode. However, the steady potential decreased with decreasing [Ca], and in 5 X mM [Ca], the oocyte membrane behaved like a NaCl electrode. Studies on the steady potential as a function of "a],,, [Kl0 and [CI], in 1.0 mM C a + + or Ca-free solutions suggest that Ca++ controls the passive permeability of the oocyte membrane to Na+ and C1-. In the ovulated unfertilized egg the K+ selectivity of the cell membrane disappeared and the system behaved like a NaCl electrode. No effect of external Ca++ or K+ concentration changes on the steady potential was observed.

These results indicate that the ion permeability properties of the ovulated egg are similar to that of the ovarian oocyte in Ca-deficient medium, and suggests that the mechanism of ovulation may involve the removal of Ca++ regulation of ion permeability of the egg cell membrane.