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 omega-conotoxin. The low-threshold current was also reduced by nimodipine but was insensitive to Bay K 8644 and omega-conotoxin. The properties of the currents were consistent with different underlying Ca2+ channel types.