Cytoskeletal elements link calcium channel activity and the cell cycle in early sea urchin embryos

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Abstract
Using the whole-cell clamp technique, we show that L-type calcium channels are activated in early sea urchin blastomeres during M-phase and subsequently inactivated in S-phase. This cyclical channel behaviour occurs in the absence of the nucleus suggesting cytoplasmic regulation independent of the centrosome cycle. Puromycin at 100–400 μM does not prevent inactivation of the current showing that this phase, at least, does not require protein synthesis. Cytochalasin B at 2 μg/ml inhibits the cyclical activity in both M and S phases, while 100 μg/ml of colchicine inactivates the L-type current in M-phase and activates a large T-type calcium current in S-phase, suggesting that channel behaviour is regulated by cytoskeletal elements. Since, fragmentation experiments show the calcium channels to be clustered in the apical membrane, and some L-type calcium channel inhibitors induced a significant delay in the cell cycle, the channel may play a role in regulating cytokinesis possibly by contributing to local intracellular calcium gradients.