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Potassium single-channel properties in normal and Rous sarcoma virus-transformed chicken embryo fibroblasts
H Draheim1, H Repp, N Malettke
1Rudolf-Buchheim-Institut für Pharmakologie der Justus-Liebig-Universität Giessen, Germany.
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 micron2. All three types of channels are highly selective for K+ ions, they are Ca(2+)- 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.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Ion channels in chicken cells were studied. While normal and Rous sarcoma virus-transformed cells share some ion channel characteristics, key differences in K186 channel activation and sensitivity were observed.
Area of Science:
- Cellular Biology
- Ion Channel Physiology
- Virology
Background:
- Ion channels are crucial for cellular function, regulating membrane potential and ion transport.
- Rous sarcoma virus (RSV) transformation alters cellular properties, potentially affecting ion channel behavior.
Purpose of the Study:
- To investigate and compare ion channel properties in normal and RSV-transformed chicken embryo fibroblasts (CEFs).
- To identify specific differences in ion channel activity and regulation between normal and transformed cells.
Main Methods:
- Patch-clamp technique was employed to record single-channel currents.
- Analysis of ion channel conductances, selectivity, Ca2+ and voltage dependence, and block by tetraethylammonium.
Main Results:
- Three types of K+-selective ion channels (186 pS, 110 pS, 65 pS) were identified with identical conductances and densities in both normal and RSV-transformed CEFs.
- Significant differences were observed in the K186 channel: normal CEFs showed activation at ~1 nM Ca2+ and insensitivity to charybdotoxin, while RSV-transformed CEFs required ~100 nM Ca2+ for activation and were sensitive to charybdotoxin.
- K186 channel open state probability differed, with normal CEFs reaching 0.94 at +50 mV, compared to 0.70 in RSV-transformed CEFs.
Conclusions:
- While basic ion channel structures are conserved, RSV transformation distinctly alters the functional properties of specific channels, particularly the K186 channel.
- These alterations in K186 channel behavior may contribute to the phenotypic changes observed in RSV-transformed cells.