Extracellular signals and embryonic development

[nautica]

Suspending clam eggs in seawater containing 60 mM KCl triggers intracellular changes but if the sea water lacks calcium it prevents the activation by the 60 mM KCl.

1) What does this suggest about the mechanism of KCl activation?

I know that the membrane potential is maintained by the K leak channels. And although Cl- ions equilibrate across the membrane, the membrane potential keeps most of these ions out of the cell b/c of their negative charge. Therefore, the change in extracellular signals induce an increase in cytosolic Ca level. In egg cells, a sudden rise in cytosolic Ca concentration triggers a Ca wave that is responsible for the onset of embryonic developement. This suggest that the KCl is only an extra cellular signal and the Ca is responsible for the intracellular development or changes.


2) What would happen if the calcium ionophore was added to a suspension of eggs in a) regular seawater or b) calcium-free seawater.

I am having a bit more trouble with this one. But, I would assume that in both regular and calcium free sea water it will induce embryonic developement. That is assuming that the Ca Ionophore actually contains calcium.

Do I seem to be on the right track with both of these? Is there something I am missing?

Thanks
Nautica

 

[nautica]

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[Moonbear]

The ionophore wouldn't imply addition of calcium. A calcium ionophore would help transport Ca across a membrane. The question doesn't indicate if there is any directionality to it, so I can only assume it would just more readily allow calcium across the membrane in any direction, so it still seems Ca would still be diffusing toward the direction of lowest concentration.