High- and low-threshold calcium currents in neurons acutely isolated from rat sensorimotor cortex

Neurons were isolated by papain treatment and trituration of the frontoparietal cortex of 14 to 28-day-old rats. Whole cell voltage clamp revealed a slowly inactivating high-threshold Ca²⁺ current, activated positive to −45 mV, and a transient low-threshold Ca²⁺ current, activated positive to −65 mV. The high-threshold current was more sensitive to block by Cd²⁺ and the low-threshold current was more sensitive to block by Ni²⁺. Replacement of Ca²⁺ by Ba²⁺ increased the high-threshold current and reduced the low-threshold current. The high-threshold current was enhanced by Bay K 8644 and reduced by nimodipine and ω-conotoxin. The low-threshold current was also reduced by nimodipine but was insensitive to Bay K 8644 and ω-conotoxin. The properties of the currents were consistent with different underlying Ca²⁺ channel types.