Dependence of surfactant function on extracellular pH: mechanisms and modifications

Area of Science:

• Pulmonary physiology
• Biochemistry
• Surface chemistry

Background:

• Lung surfactant maintains alveolar stability by reducing surface tension.
• Alterations in pH can affect surfactant composition and function.
• Calf lung surfactant extract (CLSE) is a common model for studying surfactant properties.

Purpose of the Study:

• To investigate the effects of pH on natural lung surfactant and CLSE surface properties.
• To determine the role of surfactant protein A (SP-A) and lipid concentration in mitigating pH-induced changes.
• To assess the impact of pH on the ability of CLSE to restore lung mechanics.

Main Methods:

• Pulsating bubble surfactometry was used to measure surface tension.
• Experiments were conducted at varying pH levels (around 7.4 and higher).
• Albumin inactivation and excised rat lung mechanics were assessed.

Main Results:

• Increasing pH (> 7.4) reduced CLSE's ability to achieve low minimum surface tension and increased albumin sensitivity.
• Natural lung surfactant mixtures showed less impairment compared to CLSE.
• Addition of SP-A or increased lipid concentration reversed detrimental effects on surface tension.
• Alkalinization impaired CLSE's ability to restore normal lung mechanics in surfactant-deficient lungs.

Conclusions:

• High pH (> 7.4) negatively impacts lung surfactant function, particularly CLSE.
• SP-A and hydrophobic proteins cooperate to maintain low surface tension at alkaline pH.
• Maintaining appropriate pH is crucial for optimal lung surfactant performance and lung mechanics.