Calcium currents of neuroblastoma × glioma hybrid cells after cultivation with dibutyryl cyclic AMP and nickel

The long-term modulation of calcium (Ca²⁺) currents (I_Ca) was studied in 108CC15 neuroblastoma × glioma hybrid (N×G) cells grown under various culture conditions. The following results were obtained: 1. Addition of 1 mM dibutyryl cyclic adenosine monophosphate (db-cAMP) or 0.1 μM forskolin to the culture medium increased a transient component of I_Ca two-fold within 3 days, from 21.0±1.6 pA/pF (n=22) to a maximum of 40.0±2.6 pA/pF (n=28). Under these conditions, cells also expressed a slowly inactivating I_Ca component (maximum after 3 days, 20.5±1.6 pA/pF, n=28). 2. The fast inactivating I_Ca as well as the db-cAMP-induced slowly inactivating I_Ca were completely down-regulated during incubation of NxG cells with the inorganic Ca²⁺ channel blocker, nickel (Ni²⁺, 100 μM). The suppressing effect was reversed within 3 days of incubation in db-cAMP-containing medium lacking Ni²⁺. 3. Binding studies on membrane preparations of control and Ni²⁺-pretreated NxG cells revealed a marked difference in the maximal (+)³H-PN200-110 binding. The difference was seen in undifferentiated as well as in dbc-AMP-incubated cells. 4. The protein synthesis blocker, cycloheximide, suppressed both the db-cAMP-induced increase and the reappearance of I_Ca following Ni²⁺ pretreatment. It is suggested that chronic application of db-cAMP or Ni²⁺ to NxG cells increases and decreases the number of Ca²⁺ channel proteins, respectively.