CHARACTERIZATION OF ENDOGENOUS SODIUM-CHANNEL GENE EXPRESSED IN CHINESE-HAMSTER OVARY CELLS

Chinese hamster ovary (CHO-K1) cells were observed to display transien t inward Na+ currents of average amplitude (-92 +/- 20 pA), which acti vated at voltages more than -40 mV, and peak inward currents were obse rved at potentials equal to or more than +10 mV. Inward Na+ currents i n these cells were eliminated after treatment with 500 or 50 nM tetrod otoxin (TTX), whereas 5 nM TTX resulted in 64 +/- 10% inhibition of Na + current. Using DNA primers designed to bind to the rat brain IIA Na channel subtype, we amplified specific polymerase chain reaction (PCR ) fragments from CHO-K1 poly-(A)+RNA. The cloning and sequencing of tw o of these fragments confirmed the presence of an endogenously express ed Na+ channel gene in these cells, which we have termed cho 1. Compar ison of the DNA sequence of cho 1 PCR fragments with other known Na+ c hannel genes indicated a high degree of homology with rat brain Na+ ch annel subtypes. Northern blots using riboprobes generated from the cho 1 PCR fragments revealed the presence of a specific 9-kb mRNA in thes e cells. The molecular and electrophysiological data suggest that the cho 1 Na+ channel gene from CHO-K1 cells is closely related to brain-t ype Na+ channels.