ND containing specified weight ratios of CL and PC were formulated with apoA-I in HEPES buffer. Aliquots of the different ND samples (corresponding to 78 nmol CL), were added to the wells of a 96 well microtiter plate. To each well, indicated amounts of CaCl2 were added and the volume adjusted to 200 μl with HEPES buffer. The plate was incubated for 1 h at 22 °C and, following incubation, sample absorbance at 325 nm was measured. Values reported are the mean ± standard error (n = 3) ****, P<0.0001 versus 0 nmol CaCl2. ns, not significant.