The crude venoms of the soldierfish (Gymnapistes marmoratus), the lionfish (Pterois volitans) and the stonefish (Synanceia trachynis) display pronounced neuromuscular activity. Since [Ca(2+)](i) is a key regulator in many aspects of neuromuscular function we sought to determine its involvement in the neuromuscular actions of the venoms. In the chick biventer cervicis muscle, all three venoms produced a sustained contraction (approx 20-30% of 1mM acetylcholine). Blockade of nicotinic receptors with tubocurarine (10 micro M) failed to attenuate the contractile response to either G. marmoratus venom or P. volitans venom, but produced slight inhibition of the response to S. trachynis venom. All three venoms produced a rise in intracellular Ca(2+) (approx. 200-300% of basal) in cultured murine cortical neurons. The Ca(2+)-channel blockers omega-conotoxin MVIIC, omega-conotoxin GVIA, omega-agatoxin IVa and nifedipine (each at 1 micro M) potentiated the increase in [Ca(2+)](i) in response to G. marmoratus venom and P. volitans venom, while attenuating the response to S. trachynis venom. Removal of extracellular Ca(2+), replacement of Ca(2+) with La(3+) (0.5mM), or addition of stonefish antivenom (3units/ml) inhibited both the venom-induced increase in [Ca(2+)](i) in cultured neurones and contraction in chick biventer cervicis muscle. Venom-induced increases in [Ca(2+)](i) correlated with an increased cell death of cultured neurones as measured using propidium iodide (1 micro g/ml). Morphological analysis revealed cellular swelling and neurite loss consistent with necrosis. These data indicate that the effects of all three venoms are due in part to an increase in intracellular Ca(2+), possibly via the formation of pores in the cellular membrane which, under certain conditions, can lead to necrosis.