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1 Division of Pulmonary and
Critical Care Medicine,
The present
study characterizes the dynamic interfacial properties of calf lung
surfactant (CLS) and samples reconstituted in a stepwise fashion from
phospholipid (PL), hydrophobic apoprotein (HA), surfactant apoprotein A
(SP-A), and neutral lipid fractions. Dipalmitoylphosphatidylcholine
(DPPC), the major PL component of surfactant, was examined for
comparison. Surface tension was measured over a range of oscillation
frequencies (1-100 cycles/min) and bulk phase concentrations
(0.01-1 mg/ml) by using a pulsating bubble surfactometer. Distinct
differences in behavior were seen between samples. These differences
were interpreted by using a previously validated model of surfactant
adsorption kinetics that describes function in terms of
1) adsorption rate
coefficient (k1),
2) desorption rate
coefficient
(k2),
3) minimum equilibrium surface
tension (
*), 4) minimum surface
tension at film collapse (
min), and
5) change in surface tension with
interfacial area for
<
*
(m2). Results
show that DPPC and PL have
k1 and
k2 values several
orders of magnitude lower than CLS. PL had a
min of 19-20 dyn/cm,
significantly greater than CLS (nearly zero). Addition of the HA to PL
restored dynamic interfacial behavior to nearly that of CLS. However,
m2 remained at a
reduced level. Addition of the SP-A to PL + HA restored
m2 to a level
similar to that of CLS. No further improvement in function occurred
with the addition of the neutral lipid. These results support prior studies that show addition of HA to the PL markedly increases adsorption and film stability. However, SP-A is required to completely normalize dynamic behavior.
surface tension; dynamic; model; surfactometer
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