Inhibition of cell spreading by lysosomotropic amines

Abstract

Ammonia and various amines with weak-base properties have been shown to accumulate in acidic cellular vacuoles such as lysosomes, and to inhibit lysosomal degradative processes in several types of cells in vitro [l-l I]. In addition these compounds may: inhibit protein secretion [ 121 as well as other vesicle-mediated secretory processes [ 131, inhibit the adsorbtive uptake of macromolecules [ 14161, suppress the activity of certain receptor-dependent toxins [ 17,181, and prevent the focal patching of occupied cell-surface receptors normally preceding internalization and degradation of receptor-ligand complexes [ 191. That all of these effects are observed only at relatively high amine concentrations (2-10 mM) may indicate that they are consequential of a generalized perturbation of cellular membrane mobility, caused by the accumulation of amines in certain compartments of the cellular membrane system. Isolated rat hepatocytes have been shown to attach to and spread readily on substrata of adsorbed serum (fibronectin) or collagen [20-221, and scanning electron microscopy has revealed that the spreading is mediated by a continuous flow of a thin, basal layer of lamellar cytoplasm [21] directed towards the cell periphery. A general interference with cellular membrane flow might therefore be expected to cause inhibition of hepatocyte spreading, and such inhibition by lysosomotropic amines is demonstrated here. 2. Materials and methods