Albumin in monocyte function assays. Differential stimulation of superoxide or arachidonate release by calcium ionophores.

Peripheral blood monocytes release superoxide (O2-) and arachidonic acid (AA) when stimulated with 12-O-tetradecanoate phorbol-13-acetate (TPA) or calcium ionophores (A23187 or ionomycin). In vitro assays of AA or O2- release performed in the presence of albumin failed to detect superoxide production when ionophore was used as the stimulating agent. Raising the concentration of ionophore or reducing the BSA concentration balanced one another in terms of detection of superoxide release. Binding of ionophore by albumin, which reduced the effective concentration of the stimulating agent, most likely accounted for this effect, but a small component could be attributed to calcium binding by albumin as well. These results indicate differing susceptibilities of monocyte functions to stimulation by increased intracellular Ca2+. Under strictly defined conditions, superoxide and arachidonate release may be assayed simultaneously. Binding of ionophores (and, by analogy, other agents) to albumin must be taken into account when determining stimulating doses for use in monocyte function assays.