The earliest membrane responses to phagocytosis: membrane potential changes and Ca++ loss in human granulocytes

The two findings reported here clearly indicate that the human granulocyte undergoes stimulus-secretion coupling when appropriate stimuli engage the cell surface. These secretory and metabolic responses seem designed to provide efficient mechanisms for bacterial killing or the elimination of immune complexes. First, ligands bind to surface receptors, in the case of concanavalin A, via surface sugars, in the case of immune complexes, via Fc receptors. Our new findings, described above, show that this is followed within five to ten seconds by membrane hyperpolarization: changes in the membrane potential of the cell: delta psi. Local loss of membrane calcium is noted concurrently: not as part of a generalized "triggering" of all the surface membraneof the cell, but only at the point of ligand-receptor interaction: the initiating point of phagocytosis. The subsequent changes, such as superoxide anion production, the generation of thromboxanes and prostaglandins, and the intracellular events which lead to secretion appear, therefore, to be secondary to these earliest membrane responses of phagocytosis.