FIGURE 4.

²H-NMR spectra of POPC membranes deuterated at the cis-double bond of the sn-2-oleic acyl chain and suspended in buffer with various verapamil concentrations. Approximately twenty-five milligrams of lipid suspended in 50 μL buffer (MES 25 mM + 0.1 M NaCl, pH 5.5) were used. The verapamil/lipid molar ratios from bottom-to-top are 0.003, 0.021, 0.037, and 0.048. The smooth lines are the simulated deuterium NMR spectra. The lower panel shows the loss in signal intensity of the C-9′ and C-10′ deuteron as a function of the verapamil/lipid molar ratio referenced to the pure POPC spectrum. The C-9′ deuteron with a 13 kHz splitting shows a much steeper intensity loss than the C-10′ deuteron with a 2 kHz splitting. (4 K free induction decays for all spectra.)