Development of Sodium Channel Protein During Chemically Induced Differentiation of Neuroblastoma Cells

We have previously shown that the 3H]saxitoxin binding site of the sodium channel is expressed independently of the 125I]scorpion toxin binding site in chick muscle cultures and in rat brain. In the present work, we studied the development of the sodium channel protein during chemically induced differentiation of N1E-115 neuroblastoma cells, using 3H]saxitoxin binding, 125I]scorpion toxin binding, and 22Na uptake techniques. When grown in their normal culture medium, these cells are mostly undifferentiated, bind 90 +/- 10 fmol of 3H]saxitoxin/mg of protein and 112 +/- 14 fmol of 125I]scorpion toxin/mg protein, and, when stimulated with scorpion toxin and batrachotoxin, take up 70 +/- 5 nmol of 22Na/min/mg of protein. Cells treated with dimethyl sulfoxide (DMSO) or hexamethylene-bis-acetamide (HMBA) differentiate morphologically within 3 days. At this time, the 3H]saxitoxin binding, the 125I]scorpion toxin binding, and the 22Na uptake values are not very different from those of undifferentiated cells. With subsequent time in DMSO or HMBA, these values continue to increase, a result indicating that the main period of sodium channel expression occurs well after the cells have assumed the morphologically differentiated state. The data indicate that the expression of sodium channels and morphological differentiation are independently regulated neuronal properties, that the attainment of morphological differentiation is necessary but not in itself sufficient for full expression of the sodium channel proteins, and that, in contrast to the chick muscle cultures and rat brain, the 3H]saxitoxin site and 125I]scorpion toxin site appear to be coregulated in N1E-115 cells.