Figure 1.

Biochemical signaling pathways that result in increased intracellular calcium concentration ([Ca²⁺]_i). Different cell processes can lead to the influx of extracellular Ca²⁺ or the release of Ca²⁺ from the intracellular stores, both leading to increased [Ca²⁺]_i. When assessing the effects of venom component toxins by constellation pharmacology using high extracellular potassium [K⁺] pulses (e.g., 25 mM KCl) as a depolarizing stimulus, three different effects could be observed according to the interaction of the venom components to one or more of the mechanistic pathways depicted here: amplification (phenotype A), which augments or prolongs subsequent membrane depolarization duration (e.g., potential mechanisms include blocking voltage-gated potassium channels or delayed inactivation of sodium channels); inhibition (phenotype B), which decreases or shortens the membrane depolarization duration (e.g., potential mechanisms include blocking voltage-gated sodium or calcium channels or activation of hyperpolarizing ion channels including GABA or glycine receptors); and direct effects (phenotype C) on voltage-gated ion channels and ligand-gated ion channels, including G-protein coupled receptors (GPCRs), causing a depolarizing elevation of cytosolic calcium levels. Finally, as with other calcium imaging-based assays, calcium ionophores and cytolytic events involving the loss of cell membrane integrity can result in a transient increase in the intracellular Ca²⁺, which is most often irreversible and leads to cell death with leakage of the Fura-2.