Effect of different phospholipids on connexin hemichannel activity in liposomes. The activity of homomeric Cx26 (squares) and Cx32 (circles) channels was assessed in isoosmotic density centrifugation gradients to separate liposomes containing functional channels from those that do not on the basis of channel permeability to gradient osmolytes (Transport Specific Fractionation, TSF). Activity is measured as the percentage of liposomes containing functional channels compared with the control (a). Control liposome composition was (mol:mol) 2PC:PS and approx. 0.02 mol% DOPE-NBD or DOPE-rhodamine. EPC = ethylphosphatidylcholine; DOPE = dioleoylphosphatidylethanolamine; DOPE-NBD and DOPE-rhodamine = DOPE headgroup labeled with nitrobenzoxadiazole (NBD) or lissamine rhodamine B (rhodamine), respectively. Other abbreviations as in Figure 1. (b) The activity data from (a) was plotted as a function of calculated zeta potential. Zeta potentials were calculated from McLaughlin  and Winiski et al. , adjusted for TSF conditions of pH 7.6 and 46.4 mM salt. pK of 8.5 was used to calculate the charge of PE (see text). For (b), numbers 1 to 11 next to the data points refer to the compositions/channels shown in (a). n equals three to six trials per data point.