LIPID-ION CHANNEL INTERACTIONS - INCREASING PHOSPHOLIPID HEADGROUP SIZE BUT NOT ORDERING ACYL CHAINS ALTERS RECONSTITUTED CHANNEL BEHAVIOR

We have recently shown (Chang et al., 1995) that lipid-channel interac tions, exemplified by the effects of cholesterol on the calcium-activa ted potassium (BK) channel, profoundly affect channel properties. The present study further explores such interactions by monitoring changes in BK channel behavior after reconstitution into bilayers where the s ize of phospholipid (PL) headgroups is increased and where the freedom of motion (inverse order) of fatty acid chains is incremented. Increa sing the PL headgroup cross-sectional area, from that of N-meth-DOPE t o that of DOPC (an increase from ca. 60 to 70 Angstrom(2)), is associa ted with a doubling of the channel mean opentime. Channel conductance, however, was unaffected. Increasing the order of the fatty acid chain s, from that of DOPE to POPE and to that of DEPE, had no significant e ffect on channel properties (at 22 degrees C). We interpret the change s reported here to reflect lipid-protein interactions through the indu ction of structural stress related to the headgroup structures of phos pholipids.