Effects of Anthopleurin-Q on the Intracellular Free Ca2+ Concentration in Cultured Rat Cortical Neurons

Abstract

The present study was designed to investigate the mechanism underlying the intracellular free Ca(2+) concentration ([Ca(2+)]i) modulated by Anthopleurin-Q (AP-Q), a sea anemone toxin, using whole-cell patch clamp and fluorescence digital imaging techniques. Results indicated that the overall Ca(2+) concentration could be augmented in presence of AP-Q. The increase of [Ca(2+)]i induced by AP-Q was eliminated in Na(+)-free solution, Ca(2+)-free solution or in presence of TTX. However, the Ca(2+) increase induced by AP-Q could not be influenced by cyclopiazonic acid (CPA), a specific inhibitor of the endoplasmic reticulum Ca(2+)-ATPase pump. We furthermore demonstrated that voltage-gated calcium channels (VGCCs) blocker verapamil, or inhibitor of the reverse operation Na(+)-Ca(2+) exchanger NiCl2 attenuated AP-Q-induced [Ca(2+)]i elevation. Furthermore, the inactivation process of Na(+) current (I Na ) was significantly delayed with slightly change of its amplitude by AP-Q. These findings demonstrated that neuron voltage-gated Na(+) channels are also targets of AP-Q. Overall, the present results suggested that AP-Q induced calcium influx via Na(+)-dependent activation of voltage-gated sodium channels (VGSCs), VGCCs and reverse operation of the Na(+)/Ca(2+)exchanger.