Interaction of filamentous actin with isolated liver plasma membranes.

Actin-membrane interactions have been studied using purified liver plasma membranes and muscular filamentous actin. Despite the large quantity of endogenous actin present in membranes, exogenous muscular filamentous actin cosediments with membranes after a 30 min centrifugation at 30 000 g. The cosedimentation process is time-dependent and exhibits a complex relationship with actin concentration. The cosedimentation of actin with membranes can be partly explained by gelation as shown by low-shear viscosity and electron microscopy. The characterization of the gelation phenomenon as a function of time, actin and membrane concentrations, ionic strength, temperature and Ca2+ concentration is also presented. Gelation alone cannot however account for the overall cosedimentation data, and a more direct mode of association between actin and the membrane must be envisaged. The analogy that exists between the results obtained with liver plasma membranes and those obtained with other membrane systems suggests that a general mechanism may be involved in the interaction of actin with plasma membranes.