Changes in the flow properties of phospholipid dispersions induced by procaine hydrochloride. Effect of pH and temperature.

Since local anaesthetics are known to interact with membrane lipids, we have examined the changes taken place by procaine hydrochloride in lipid matrices as a function of pH. Rheological methods might give useful information on the association of this anaesthetic with soybean lecithin. The procaine interacted with negatively charged phospholipid polar head groups at pH 4. This system exhibits a loosening in the tight arrangement of phospholipid molecules caused by the addition of procaine as a function of this anaesthetic's concentration. The flow enthalpy values as a function of procaine-lipid ratio shows biphasic behaviour and suggests a phase transition when the anaesthetic concentration goes from 10 to 14 mM and temperatures dip below 10 degrees C.