Potassium single-channel properties in normal and Rous sarcoma virus-transformed chicken embryo fibroblasts

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Abstract
Ion channels in normal and Rous sarcoma virus (RSV)-transformed chicken embryo fibroblasts (CEFs) were examined by using the patch-clamp technique. Three different types of ion channels were observed with single-channel conductances in symmetrical 140 mM KCl (with frequencies of occurrence in parentheses) of 186 pS (70%), 110 pS (10%), and 65 pS (20%), which are identical in normal and RSV-transformed CEFs. The total channel density in both cell types is about 0.13 per μm+. All three types of channels are highly selective for K+ ions, they are Ca2+- and voltage-dependent, and they can be completely blocked by external tetraethylammonium (10 mM) in both normal and RSV-transformed cells. Some channel properties, however, are different in normal and RSV-transformed CEFs. The K186 channel of normal CEFs is almost completely activated in the presence of about 1 nM free internal Ca2+ and is insensitive to charybdotoxin (100 nM). In contrast, the K186 channel of RSV-transformed CEFs has an EC50 value for activation by internal Ca2+ of about 100 nM and is highly sensitive to charybdotoxin (IC50=9 nM). In normal CEFs, the K186 channel activity starts at membrane potentials more positive than −50 mV and reaches a high open state probability of 0.94 at +50 mV. In RSV-transformed CEFs, the threshold of K186 channel activity is also −50 mV but the maximal open state probability is only 0.70 at +50 mV membrane potential. Averages of current traces of K186 channels show the typical features of the macroscopic K+ currents described previously for normal and RSV-transformed CEFs. However, one of the properties of the whole-cell current of normal CEFs, i.e. the inactivation during prolonged membrane depolarization, could not be observed at the single-channel level. Nevertheless, we suggest that the K186 channel is the main contributor to the macroscopic K+ currents both in normal and RSV-transformed CEFs.