Activation of anion channels by zymosan particles in membranes of peritoneal macrophages.

Patch-clamp recordings were used to study the effect of zymosan adsorption on membranes of freshly isolated peritoneal macrophages of mouse. Superfusion of adherent macrophages by zymosan in the on-cell pipette configuration stimulated the appearance of anion channels after a varying time delay in the minute range. The channel is activated by passing through a stage of fluctuations of increasing amplitude. Once the full channel current has been reached, the fluctuations become transformed into the typical current pattern of three well-defined conducting channel states. The adoption of the two substates appeared to be dependent on zymosan. Up to nine simultaneously open anion channels could be observed with a single channel conductance of 220-400 pS. Absence of external Ca2+ had no inhibiting influence on the effect of zymosan. Anion channels could in some cases be observed under control conditions, after attachment of the pipette to the membrane. The channel activation could be mimicked by addition of A23187 to calcium-containing bath solutions. There is evidence that a zymosan-mediated rise of intracellular Ca2+ might be involved in the stimulus response coupling. The activation of calcium-dependent potassium channels was not observed.