Cobalt-ions dissociate between calcium uptake through voltage-dependent sodium and calcium channels in synaptosomes

Calcium ions are taken up through at least two separate, voltage-dependent channels in rat cortical synaptosomes. One channel is opened by 60 mM K+, blocked completely with 500 microM Co2+ and unaffected by 1 microM tetrodotoxin; the other is opened by 20 microM veratridine in a sodium-independent manner, blocked by 1 microM tetrodotoxin, and only partially inhibited by Co2+. Calcium-uptake through either channel is functional with respect to releasing [3H]ACh.