Evidence for a K+ channel in bovine chromaffin granule membranes: single-channel properties and possible bioenergetic significance

• Published in: European biophysics journal 1994-10, Vol.23 (4), p.263-275
• Main Authors: Ashley, R H, Brown, D M, Apps, D K, Phillips, J H
• Format: Article
• Language: English
• Subjects: Adrenal Medulla - physiology; Animals; Calcium - pharmacology; Cations, Monovalent - metabolism; Cattle; Charybdotoxin; Chromaffin Granules - physiology; Intracellular Membranes - drug effects; Intracellular Membranes - physiology; Kinetics; Lipid Bilayers; Membrane Potentials - drug effects; Potassium Channels - analysis; Potassium Channels - drug effects; Potassium Channels - physiology; Proton-Translocating ATPases - metabolism; Scorpion Venoms - pharmacology
• ISSN: 0175-7571; 1432-1017
• DOI: 10.1007/BF00213576

A K+ channel was incorporated into voltage-clamped planar lipid bilayers from bovine chromaffin granules and resealed granule membranes ("ghosts"). It was not incorporated from plasma membrane-rich fractions from the adrenal medulla. The channel had a conductance of approximately 400 pS in symmetric 450 mM KCl, with the permeability sequence K+ > Rb+ > Cs+ > Na+ > Li+, and was insensitive to both Ca2+ and charybdotoxin. It exhibited complex gating kinetics, consistent with the presence of multiple open and closed states, and its gating was voltage-dependent. The channels appeared to incorporate into bilayers with the same orientation, and were blocked from one side (the side of vesicle addition) by 0.2-1 mM TEA+. The block was slightly voltage-dependent. Acidification of resealed granule membranes in response to external ATP (which activated the vacuolar-type ATPase) was significantly reduced in the presence of 1 mM intralumenal TEACl (with 9 mM KCl), and parallel measurements with the potential-sensitive dye Oxonol V showed that such vesicles tended to develop higher internal-positive membrane potentials than control vesicles containing only 10 mM KCl. 1 mM TEA+ had no effect on proton-pumping activity when applied externally, and did not directly affect either the proton-pumping or ATP hydrolytic activity of the partially-purified ATPase. These results suggest that chromaffin granule membranes contain a TEA(+)-sensitive K+ channel which may have a role in regulating the vesicle membrane potential.