Characterisation of a cell swelling-activated K+-selective conductance of Ehrlich mouse ascites tumour cells

摘要

class="enumerated" style="list-style-type:decimal">The K⁺ and Cl⁻ currents activated by hypotonic cell swelling were studied in Ehrlich ascites tumour cells using the whole-cell recording mode of the patch-clamp technique.Currents were measured in the absence of added intracellular Ca²⁺ and with strong buffering of Ca²⁺. K⁺ current activated by cell swelling was measured as outward current at the Cl⁻ equilibrium potential (ECl) under quasi-physiological gradients. It could be abolished by replacing extracellular Na⁺ with K⁺, thereby cancelling the driving force. Replacement with other cations suggested a selectivity sequence of K⁺ > Rb⁺ > NH4≈ Na⁺≈ Li⁺; Cs⁺ appeared to be inhibitory.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.The class III antiarrhythmic drug clofilium blocked the volume-sensitive K⁺ current in a voltage-independent manner with an IC50 of 32 μM. Clofilium was also found to be a strong inhibitor of the regulatory volume decrease response of Ehrlich cells.Cell swelling-activated K⁺ currents of Ehrlich cells are voltage and calcium insensitive and are resistant to a range of K⁺ channel inhibitors. These characteristics are similar to those of the so-called background K⁺ channels.Noise analysis of whole-cell current was consistent with a unitary conductance of 5.5 pS for the single channels underlying the K⁺ current evoked by cell swelling, measured at 0 mV under a quasi-physiological K⁺ gradient.