EFFECTS OF MECHANO-GATED CATION CHANNEL BLOCKERS ON XENOPUS OOCYTE GROWTH AND DEVELOPMENT

The putative role(s) of a mechanically gated (MG) cation channel in Xe nopus oocyte growth, maturation, fertilization and embryogenesis has b een examined. Using a pharmacological approach, we have tested the eff ects of the MG channel blockers, gadolinium, gen tamicin and amiloride on the above developmental events. Our results indicate that oocyte m aturation, fertilization and early embryogenesis (up to the free-swimm ing stage 45) can proceed normally in the presence of concentrations o f agents that either completely abolish (i.e., greater than or equal t o 10 mu M Gd3+) or partially block(i.e., 1 mM gentamicin) single MG ch annel activity as measured by patch-clamp recording. However, we also find that higher concentrations of Gd3+ (greater than or equal to 50 m u M) can lead to an increased percentage (>20%) of axis-perturbed embr yos compared with control (<1%) and that amiloride (0.5 mM) reduces th e success of fertilization (from 100% to <50%) and increases mortality (by similar to 75%) in developing embryos. Furthermore, we find that all three agents inhibit oocyte growth in vitro. However, their order of effectiveness (amiloride > gentamicin > Gd3+) is opposite to their order for blocking MG channels (Gd3+ much greater than gentamicin > am iloride). These discrepancies indicated that the drugs effects occur b y mechanisms other than, or in addition to, MG channel block. Our resu lts provide no compelling evidence for the idea that MG channel activi ty is critical for development in Xenopus. This could mean that there are other mechanisms in the oocyte that can compensate when MG channel activity is blocked or that the protein that forms the channel can un dergo additional interactions that result in a function insensitive to MG channel blockers.