An endogenous acid-sensitive K⁺ channel expressed in COS-7 cells

COS-7 cells originally isolated from monkey kidney and used in many transfection studies were found to express a background K⁺ channel and therefore, its biophysical and pharmacological properties were examined. In cell-attached patches, a 32-pS K⁺ channel with a linear current-voltage relationship could be recorded. The open probability was highly voltage-dependent, with greater channel activity at depolarized potentials. The channel was markedly sensitive to changes in extracellular pH (pH_o), showing a 70 ± 10% inhibition by changing the pH_o from 7.3 to 6.3. Arachidonic acid (5 μM) augmented channel activity 12-fold. Applying negative pressure (-40 mmHg) to the membrane patch also increased channel activity by 4-fold. These results show that COS-7 cells express a K⁺ channel with unique properties that must be considered when using these cells as transfection system.