RESUMO
The membrane currents of chicken embryo fibroblasts (CEFs) transformed by Rous sarcoma virus (RSV) were compared with the currents of their nontransformed counterparts by using the whole-cell patch-clamp technique. In nontransformed CEFs, the main membrane current is a delayed outward K+ current that is sensitive to tetraethylammonium ion but insensitive to 4-aminopyridine. This K+ current is almost independent of the intracellular Ca2+ concentration and becomes completely inactivated at positive membrane potentials with a time constant of about 10 s at +30 mV. In contrast, transformed CEFs exhibit a noninactivating K+ current that strongly depends on the intracellular Ca2+ concentration. This Ca(2+)-dependent K+ current is blocked by the scorpion toxin charybdotoxin with an IC50 value of 19 nM, whereas the K+ current of normal CEFs is insensitive to charybdotoxin (up to 300 nM). The K+ current properties of transformed CEFs were also found after microinjection of purified, enzymatically active pp60v-src into normal CEFs but not after infection of CEFs with the Rous-associated virus RAV5, which lacks the v-src oncogene. Our results suggest that the oncogene product pp60v-src modulates existing K+ channel proteins, leading to profound electrophysiological and pharmacological alterations of the K+ current properties in RSV-transformed CEFs. Furthermore, our experiments identify for the first time K+ channels as possible substrates of pp60v-src.