Mi. Niemeyer et al., Characterisation of a cell swelling-activated K+-selective conductance of Ehrlich mouse ascites tumour cells, J PHYSL LON, 524(3), 2000, pp. 757-767
1. The K+ and Cl- currents activated by hypotonic cell swelling were studie
d in Ehrlich ascites tumour cells using the whole-cell recording mode of th
e patch-clamp technique.
2. Currents were measured in the absence of added intracellular Ca2+ and wi
th strong buffering of Ca2+. K+ current activated by cell swelling was meas
ured as outward current at the Cl(-)equilibrium potential (E-Cl) under quas
i-physiological gradients. It could be abolished by replacing extracellular
Na+ with K+, thereby cancelling the driving force. Replacement with other
cat;ions suggested a selectivity sequence of K+ > Rb+ > NH4 approximate to
Na+ approximate to Li+; Cs+ appeared to be inhibitory.
3. The current-voltage relationship of the volume-sensitive K+ current was
well fitted with the Goldman-Hodgkin-Katz current equation between -130 and
+20 mV with a permeability coefficient of around 10(-6) cm s(-1) with both
physiological and high-K+ extracellular solutions.
4. The class III antiarrhythmic drug clofilium blocked the volume-sensitive
K+ current in a voltage-independent manner with an IC50 of 32 mu M. Clofil
ium was also found to be a strong inhibitor of the regulatory volume decrea
se response of Ehrlich cells.
5. Cell swelling-activated K+ currents of Ehrlich cells are voltage and cal
cium insensitive and are resistant to ct range of K+ channel inhibitors. Th
ese characteristics are similar to those of the so-called background K+ cha
nnels.
6. Noise analysis of whole-cell current was consistent with a unitary condu
ctance of 5.5 pS for the single channels underlying the K+ current evoked b
y cell swelling, measured at 0 mV under a quasi-physiological K+ gradient.