EVIDENCE FOR A K- SINGLE-CHANNEL PROPERTIES AND POSSIBLE BIOENERGETICSIGNIFICANCE( CHANNEL IN BOVINE CHROMAFFIN GRANULE MEMBRANES )

A K+ channel was incorporated into voltage-clamped planar lipid bilaye rs from bovine chromaffin granules and resealed granule membranes (''g hosts''). It was not incorporated from plasma membrane-rich fractions from the adrenal medulla. The channel had a conductance of similar to 400 pS in symmetric 450 mM KC1, with the permeability sequence K+ > Rb + > Cs+ > Na+ > Li+, and was insensitive to both Ca2+ and charybdotoxi n. It exhibited complex gating kinetics, consistent with the presence of multiple open and closed states, and its gating was voltage-depende nt. The channels appeared to incorporate into bilayers with the same o rientation, and were blocked from one side (the side of vesicle additi on) by 0.2-1 mM TEA(+). The block was slightly voltage-dependent. Acid ification of resealed granule membranes in response to external ATP (w hich activated the vacuolar-type ATPase) was significantly reduced in the presence of 1 mM intralumenal TEAC1 (with 9 mM KC1), and parallel measurements with the potential-sensitive dye Oxonol V showed that suc h vesicles tended to develop higher internal-positive membrane potenti als than control vesicles containing only 10 mM KC1. 1 mM TEA(+) had n o effect on proton-pumping activity when applied externally, and did n ot directly affect either the proton-pumping or ATP hydrolytic activit y of the partially-purified ATPase. These results suggest that chromaf fin granule membranes contain a TEA(+)-sensitive K+ channel which may have a role in regulating the vesicle membrane potential.