Evidence for a K+ channel in bovine chromaffin granule membranes: single-channel properties and possible bioenergetic significance.
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.
Ashley
R H
RH
Department of Biochemistry, University of Edinburgh, UK.
Brown
D M
DM
Apps
D K
DK
Phillips
J H
JH
D000313:Adrenal Medulla / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002414:Cations, Monovalent / Q000378:metabolism; D002417:Cattle; D018999:Charybdotoxin; D002837:Chromaffin Granules / Q000502:physiology*; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000032:analysis / Q000187:drug effects / Q000502:physiology*; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012604:Scorpion Venoms / Q000494:pharmacology
D002414:Cations, Monovalent; D008051:Lipid Bilayers; D015221:Potassium Channels; D012604:Scorpion Venoms; D018999:Charybdotoxin; D006180:Proton-Translocating ATPases; D002118:Calcium