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

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.