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 (pHo), showing a 70 ± 10% inhibition by changing the pHo 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.