Antibody activates cationic channels via second messenger Ca2+.

Patch-clamp recordings were used to study single channels permeable to multiple cations in a macrophage cell line. At least three conductance levels were found, consistent with the existence of several types of nonselective cation channels or a single channel with multiple open states. The activity of the channels depended very little on voltage but was affected by internal Ca2+ concentration. Specific subclasses of immunoglobulins (IgG1 and IgG2b) bound to an Fc receptor on the surface of these macrophages. When an IgG2b was applied to the cell exterior after a patch pipette had been sealed in the cell-attached mode, the nonselective cation channels within the patch were activated. Thus, these channels must be modulated by a second messenger. Since antibodies binding to the Fc receptor have been shown to produce a rise in intracellular Ca2+, this cation must be considered a candidate as a second messenger that amplifies the effect of antibody in gating these channels.