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 chan nels are activated in early sea urchin blastomeres during M-phase and subsequently inactivated in S-phase, This cyclical channel behaviour o ccurs in the absence of the nucleus suggesting cytoplasmic regulation independent of the centrosome cycle, Puromycin at 100-400 mu M does no t prevent inactivation of the current showing that this phase, at leas t, does not require protein synthesis, Cytochalasin B at 2 mu g/ml inh ibits the cyclical activity in both M and S phases, while 100 mu g/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 beh aviour is regulated by cytoskeletal elements, Since, fragmentation exp eriments show the calcium channels to be clustered in the apical membr ane, and some L-type calcium channel inhibitors induced a significant delay in the cell cycle, the channel may play a role in regulating cyt okinesis possibly by contributing to local intracellular calcium gradi ents.