Enhanced expression of Ca2+ channels by nerve growth factor and the v‐src oncogene in rat phaeochromocytoma cells.

1. Rat phaeochromocytoma (PC12) cells were used to investigate the expression of Ca2+ channel types during neuronal differentiation. Neuronal differentiation was induced by treatment with nerve growth factor (NGF) or by activation of a temperature‐sensitive tyrosine kinase (pp60v‐src) in genetically modified PC12 (PC12/v‐src) cells. PC12 cells differentiated morphologically in the presence of NGF. When grown at the permissive temperature of 37 degrees C which activates the kinase activity of pp60v‐src, PC12/v‐src cells differentiated morphologically with the extension of neurites. In contrast, PC12/v‐src cells grown at the non‐permissive temperature of 40 degrees C continued to divide and were morphologically indistinguishable from control PC12 cells. 2. Whole‐cell Ca2+ currents were measured in PC12 cells using Ba2+ as the charge carrier. Ba2+ currents measured at the peak of the current‐voltage curve from a holding potential of ‐80 mV were ‐0.28 +/‐ 0.04 nA (mean +/‐ S.E.M.) in control PC12 cells compared to ‐1.25 +/‐ 0.16 nA in NGF‐differentiated cells. The current density increased from 9.4 +/‐ 0.7 pA/pF in control PC12 cells to 22.8 +/‐ 2.4 pA/pF in NGF‐differentiated PC12 cells. Ba2+ currents were ‐0.24 +/‐ 0.04 nA in undifferentiated PC12/v‐src cells grown at the non‐permissive temperature of 40 degrees C compared to ‐0.95 +/‐ 0.16 nA in differentiated PC12/v‐src cells grown at the permissive temperature of 37 degrees C. The current density increased from 4.5 +/‐ 0.5 pA/pF in PC12/v‐src cells grown at the non‐permissive temperature of 40 degrees C to 13.3 +/‐ 2.4 pA/pF in PC12/v‐src cells grown at the permissive temperature of 37 degrees C. 3. The sensitivity of Ba2+ currents to omega‐conotoxin GVIA (omega‐CgTX) was determined for currents measured at the peak of the current‐voltage curve (0 mV in 10 mM Ba2+) from a holding potential of ‐80 mV. In NGF‐differentiated PC12 cells, 10 microM omega‐CgTx inhibited 68.1 +/‐ 3.2% of the total Ba2+ current compared to 35.9 +/‐ 4.1% in control cells. The density of the omega‐CgTX‐sensitive current increased from 3.3 +/‐ 0.4 pA/pF in control cells to 15.7 +/‐ 2.0 pA/pF in NGF‐differentiated cells. In differentiated PC12/v‐src cells grown at 37 degrees C, omega‐CgTX inhibited 52.2 +/‐ 4.2% of total Ba2+ current compared to 41.1 +/‐ 3.8% in PC12/v‐src cells grown at 40 degrees C. The density of the omega‐CgTX‐sensitive current increased from 1.9 +/‐ 0.3 to 7.4 +/‐ 2.0 pA/pF with v‐src‐mediated differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)