Mechanism of action of Portuguese man-of-war venom-induced calcium uptake by cultured cells

Some cnidarians are significant public health hazards, of which Physalia physalis (Portuguese Man-of-war) is one of the most dangerous. Man-of-war nematocyst stings are common occurrences in the coastal waters of the southeastern United States, producing excruciating pain and, in extreme cases, cardiovascular collapse and death. Our laboratory has reported that Man-of-war venom is potently hemolytic and positively inotropic. In isolated rabbit atria the positive inotropy is directly proportional to extracellular calcium concentrations. Using embryonic cultured chicken heart cells, we find that Man-of-war venom produces a pronounced biphasic dose-response of {dollar}sp{lcub}45{rcub}{dollar}Ca influx. However, this biphasic dose-response is also observed on L-929, GH{dollar}sb4{dollar} C{dollar}sb1{dollar}, and FRL cells. Venom-induced calcium influx is not blocked by conventional, organic calcium channel blockers, but is blocked by divalent and trivalent metals. The dose-dependent decrease in venom-induced calcium influx at higher venom doses is accompanied by cell lysis which is also blocked by divalent metal ions. Osmotic protectants inhibit venom-stimulated release of LDH suggesting that cell lysis is of the colloid osmotic type.; Electron microscopic images of venom-treated cells show that Man-of-war venom forms pore-like structures in the membrane of target cells. We speculate that the inotropic effect of Man-of-war venom, the influx of calcium, and cell lysis all occur by permeabilizing the plasma membrane of target cells.