Figure 1.

Calcium blocks Na⁺ channels and speeds deactivation. Gates of the Na⁺ channels were activated by stepping to +60 mV and were deactivated by returning to −80 mV. g_Na is proportional to the number of Na⁺ channels that have open (activated) gates and are not Ca²⁺-blocked. Compared with 2 mM Ca²⁺, 50 mM Ca²⁺ blocks weakly at +60 mV, strongly at −80 mV. Deactivation is clearly faster in 50 mM Ca²⁺. Solutions: 2Ca 85Na and 50Ca 85Na.