β adrenergic receptor/cAMP/PKA signaling contributes to the intracellular Ca(2+) release by tentacle extract from the jellyfish Cyanea capillata

BACKGROUND: Intracellular Ca(2+) overload induced by extracellular Ca(2+) entry has previously been confirmed to be an important mechanism for the cardiotoxicity as well as the acute heart dysfunction induced by jellyfish venom, while the underlying mechanism remains to be elucidated. METHODS: Under extracellular Ca(2+)-free or Ca(2+)-containing conditions, the Ca(2+) fluorescence in isolated adult mouse cardiomyocytes pre-incubated with tentacle extract (TE) from the jellyfish Cyanea capillata and β blockers was scanned by laser scanning confocal microscope. Then, the cyclic adenosine monophosphate (cAMP) concentration and protein kinase A (PKA) activity in primary neonatal rat ventricular cardiomyocytes were determined by ELISA assay. Furthermore, the effect of propranolol against the cardiotoxicity of TE was evaluated in Langendorff-perfused rat hearts and intact rats. RESULTS: The increase of intracellular Ca(2+) fluorescence signal by TE was significantly attenuated and delayed when the extracellular Ca(2+) was removed. The β adrenergic blockers, including propranolol, atenolol and esmolol, partially inhibited the increase of intracellular Ca(2+) in the presence of 1.8 mM extracellular Ca(2+) and completely abolished the Ca(2+) increase under an extracellular Ca(2+)-free condition. Both cAMP concentration and PKA activity were stimulated by TE, and were inhibited by the β adrenergic blockers. Cardiomyocyte toxicity of TE was antagonized by β adrenergic blockers and the PKA inhibitor H89. Finally, the acute heart dysfuction by TE was antagonized by propranolol in Langendorff-perfused rat hearts and intact rats. CONCLUSIONS: Our findings indicate that β adrenergic receptor/cAMP/PKA signaling contributes to the intracellular Ca(2+) overload through intracellular Ca(2+) release by TE from the jellyfish C. capillata.