SiRNA knock-down of γ-glutamyl transpeptidase does not affect hypoxic K + channel inhibition

Abstract

Large conductance, Ca 2+-sensitive potassium (BK) channels are critical components of the O 2 signalling cascade in a number of cells, including the carotid body and central neurones. Although the nature of the BK channel O 2 sensor is still unknown, evidence suggests redox modulators might form part of the O 2 sensing channel complex. By metabolising glutathione, γ-glutamyl transpeptidase (γGT) could act as such an O 2 sensor. Western blotting and immunocytochemistry revealed high γGT expression in HEK293 cells expressing the α- and β-subunits of human recombinant BK and γGT co-immunoprecipitated with BKα. Acivicin blockade of γGT reversibly inhibited BK channels, suggesting that this BKα protein partner contributes to tonic channel activity. However, knock-out of γGT using siRNA had no effect on hypoxic BK channel inhibition. Together, these data indicate that γGT is a BKα protein partner, that its activity regulates BK channels but that it is not the BK O 2 sensor.