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

The long-term modulation of calcium (Ca2+) currents (ICa) was studied in 108CC15 neuroblastoma x glioma hybrid (NxG) 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 microM forskolin to the culture medium increased a transient component of ICa 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 ICa component (maximum after 3 days, 20.5 +/- 1.6 pA/pF, n = 28). 2. The fast inactivating ICa as well as the db-cAMP-induced slowly inactivating ICa were completely down-regulated during incubation of NxG cells with the inorganic Ca2+ channel blocker, nickel (Ni2+, 100 microM). 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 db-cAMP-incubated cells. 4. The protein synthesis blocker, cycloheximide, suppressed both the db-cAMP-induced increase and the reappearance of ICa 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.