Electrophysiology of phagocytic membranes. Role of divalent cations in membrane hyperpolarizations of macrophage polykaryons

Abstract

The electrophysiological properties of the membrane of mouse peritoneal macrophage polykaryons are studied. Slow hyperpolarizations can be elicited by iontophoretic injections of either Ca 2+ or Sr 2+ into the cytoplasm. The effect of both cations is identical, since: (1) it is invariably triggered by the cation injection, (2) the amplitude is dependent on the K + gradient, (3) quinine blocks reversibly the response to both cation injections. Mg 2+, Ba 2+ and Mn 2+ did not elicit responses when injected into the cytoplasm. Ca 2+ induced slow hyperpolarizations were reversibly blocked by the addition of Ba 2+ to the external saline, but were not affected by the presence of external tetraethylammonium chloride. Cells maintained in saline containing high concentrations of Ca 2+, Sr 2+ or Mn 2+ exhibited sustained hyperpolarizations. Quinine blocked the hyperpolarization induced by high Ca 2+ or Sr 2+, but was ineffective for the case of Mn 2+. Cells hyperpolarized by external Mn 2+ frequently exhibited nonlinear, voltage-current characteristics. Similar patterns could also be observed in a small fraction (less than 10%) of the cells in control conditions. Current-induced shifts between two stable membrane potentials were seen either in high Ca 2+ or normal medium. The great variability of the responses described for this phagocytic membrane is discussed. The evidence supports the assumption that Ca 2+ and Sr 2+ can induce transient or persistent hyperpolarized states by activating a potassium permeability. External Mn 2+ may act in part by reducing impalement-related current leakage from the phagocytic membrane.