pH modulation of large conductance potassium channel from adrenal chromaffin granules

Abstract

We report here that large conductance K⁺ selective channel in adrenal chromaffin granules is controlled by pH. We measured electrogenic influx of ⁸⁶Rb⁺ into chromaffin granules prepared from bovine adrenal gland medulla. The ⁸⁶Rb⁺ influx was inhibited by acidic pH. Purified chromaffin granule membranes were also fused with planar lipid bilayer. A potassium channel with conductance of 432±9 pS in symmetric 450 mM KCl was observed after reconstitution into lipid bilayer. The channel activity was unaffected by charybdotoxin, a blocker of the Ca²⁺-activated K⁺ channel of large conductance. It was observed that acidification to pH 6.4 cis side of the membrane lowered the channel open probability and single channel conductance. Whereas only weak influence on the single channel current amplitude and open probability were observed upon lowering of the pH at the trans side. We conclude that a pH-sensitive large conductance potassium channel operates in the chromaffin granule membrane.

• intracellular chromaffin granule potassium channel
• adrenal chromaffin granules
• bilayer lipid membranes

K_CG, large conductance potassium channel; BLM, black lipid membrane technique; I, single-channel current amplitude; U, potential; U_rev, reversal potential; τ_o, mean lifetime – open time; τ_c, mean lifetime – closed time; P_open, open-probability; TEA, tetraethylammonium

K_CG, large conductance potassium channel; BLM, black lipid membrane technique; I, single-channel current amplitude; U, potential; U_rev, reversal potential; τ_o, mean lifetime – open time; τ_c, mean lifetime – closed time; P_open, open-probability; TEA, tetraethylammonium