Am. J. Respir. Crit. Care Med.,
Volume 156, Number 4, October 1997, 1049-1057
Primary Importance of Zwitterionic Over Anionic
Phospholipids in the Surface-active Function of
Calf Lung Surfactant Extract
ZHENGDONG
WANG,
OKYANUS
GUREL,
SUSAN
WEINBACH,
and
ROBERT H.
NOTTER
Departments of Pediatrics, Environmental Medicine, and Chemical Engineering, University of Rochester, Rochester, New York
The relative contributions of zwitterionic and anionic phospholipids to the surface-active function of
calf lung surfactant extract (CLSE) were assessed by measurements of surface properties in vitro and
pressure-volume (P-V) mechanics in excised rat lungs in situ. Surface activity and mechanical effects
were compared for chromatographically purified CLSE subfractions containing the complete mix of
phospholipids (PPL) or modified phospholipids depleted in anionic components (mPPL), alone or
combined with 1.3% (by weight) of hydrophobic surfactant proteins (SP-B and SP-C). Surface pressure-time (
-t) adsorption isotherms at 37 ° C were very similar for dispersions of PPL and mPPL in a
Teflon dish with a stirred subphase to minimize diffusion resistance. Combination of either PPL or
mPPL with hydrophobic SP substantially improved adsorption, but mixtures of PPL:SP and mPPL:SP
had only small differences in -t isotherms and reached the same final equilibrium of ~ 47 mN/m
achieved by CLSE. Surface pressure-area (-A) isotherms and maximum surface pressures were also
very similar for spread films of PPL versus mPPL and PPL:SP versus mPPL:SP on the Wilhelmy balance
(23° C and 37° C). Respreading based on -A isotherm area calculations was slightly better in surface-excess films of PPL versus mPPL and PPL:SP versus mPPL:SP, but differences were minor and were
smaller at 37 ° C than at 23° C. Overall dynamic surface activity in oscillating bubble studies was not
significantly different for PPL versus mPPL or for PPL:SP versus mPPL:SP, and the latter two mixtures
both reached minimum surface tensions < 1 mN/m (37° C, 20 cycles/min, 0.5 mM phospholipid). Dispersions of PPL:SP, mPPL:SP, and CLSE were also not significantly different in improving P-V mechanics almost to normal when instilled in lavaged, excised rat lungs at 37 ° C (30 mg/2.5 ml saline).
These data suggest that zwitterionic phospholipids have a major role over anionic phospholipids in
interacting with hydrophobic SP in the adsorption, dynamic surface tension lowering, film respreading, and pulmonary mechanical activity of the hydrophobic components of calf lung surfactant in
CLSE.
