Palytoxin-induced increase in endothelial Ca2+ concentration in the rabbit aortic valve

Abstract

Palytoxin (PTX) is one of the most potent toxins isolated from marine coelenterates of the genus Palythoa. It induces depolarization in various types of cells by increasing the permeability for monovalent cations. It has been reported that PTX induces endothelium-dependent relaxation of vascular smooth muscle. In this study, we examined the effect of PTX on the cytosolic Ca2+ concentration ([Ca2+]i) in the endothelium of rabbit aortic valves loaded with fluorescent Ca2+ indicators, fura-PE3 or fluo-3. PTX (10 pM-300 nM) irreversibly increased endothelial [Ca2+]i in a concentration-dependent manner. ATP and thapsigargin also increased [Ca2+]i. Imaging of [Ca2+]i with a confocal microscope revealed that PTX increased [Ca2+]i in all endothelial cells studied (n = 13). An inorganic Ca2+ entry blocker, La3+ (30 microM), had no effect on the increase in [Ca2+]i induced by PTX whereas it inhibited the sustained phase of the increase in [Ca2+]i induced by ATP or thapsigargin. The PTX-induced increase in [Ca2+]i was partially inhibited by ouabain and was abolished by removal of external Ca2+ although decrease of Na+ concentration in the incubation medium was ineffective. Activation of protein kinase C by 1 microM 12-deoxyphorbol 13-isobutyrate or inhibition of phosphatase by 10 nM calyculin-A had no effect on the increase in [Ca2+]i induced by PTX, whereas both agents inhibited the sustained phase of the increase in [Ca2+]i induced by ATP or thapsigargin. Mn2+ influx, measured by the quenching of fura-PE3 fluorescence, was accelerated by ATP or thapsigargin, but not by PTX. These results suggest that PTX increases [Ca2+]i in the endothelium of the rabbit aortic valve by increasing Ca2+ influx through a pathway which is different from that activated by ATP or thapsigargin.

The cytoskeleton, a structure that is susceptible to the toxic mechanism activated by palytoxins in human excitable cells

“…It has been reported that the elevation of cytosolic Ca 2+ induced by palytoxin is dependent on extracellular Ca 2+ [12,17,18,[34][35][36]. Our assays using neuroblastoma cells also indicated that palytoxin, as well as ostreocin-D, evoked Ca 2+ entry from the external medium.…”

Actin cytoskeleton of rabbit intestinal cells is a target for potent marine phycotoxins

“…It is known that changes in the intracellular concentration of ions caused by palytoxin implicate Ca 2+ . In fact, previous investigations revealed that the palytoxin effect on cytosolic Ca 2+ is dependent on extracellular Ca 2+ (Frelin and Van Renterghem, 1995;Amano et al, 1997;Ishii et al, 1997;Satoh et al, 2003). Within this context, and taking into account that palytoxin administered intraperitoneally caused intestinal injuries in mice (Ito et al, 1996), it would be interesting to see the effect of palytoxin and ostreocin-D on the microfilament network of intestinal cells and also to study whether Ca 2+ movements are playing any role in this effect.…”

“…Our goal was therefore to investigate the effect of PTX-6, YTX, CTX-3C, MTX, palytoxin, ostreocin-D, Pbtx-3 and Pbtx-9 on the actin cytoskeleton of freshly isolated enterocytes. We selected carefully the concentration of each toxin, noting previous studies carried out in other cellular models by our laboratory and reported in the literature (Amano et al, 1997;De la Rosa et al, 2001;Leira et al, 2002;Alfonso et al, 2003;Louzao et al, 2004). In the case of ostreocin-D, an analogue of palytoxin, we used the same concentration as with I. R. Ares and others PTXs and YTXs are marine toxins originally associated with DSP.…”

Store-Operated Calcium Channels Are Involved in Spontaneous Slow Calcium Oscillations in Striatal Neurons

“…To examine whether SOCCs are responsible for maintaining high [Ca 2+ ] i in striatal GABAergic neurons exhibiting spontaneous slow Ca 2+ oscillations, we first tested the contribution of Ca 2+influx from the extracellular space in striatal GABAergic neurons with and without slow Ca 2+ oscillations by quantifying the time constant of fluorescence quench (Figures 2A,B). More Mn 2+ entry from the extracellular space caused faster fluorescence quench (Amano et al, 1997;Uehara et al, 2002;Tu et al, 2009). The Fura-2 LR fluorescence quench was observed after MnCl 2 (50 µM) administration in the neurons with slow Ca 2+ oscillations ( Figure 2B).…”

“…Mn 2+ can pass through opened Ca 2+ -permeable channels and quenches the Fura-2 LR fluorescence emission (Amano et al, 1997;Kikuta et al, 2015). Thus, to evaluate Ca 2+ influx from the extracellular space, the rate of the quench by Mn 2+ was quantified as ∆ F/F at 380 nm (Uehara et al, 2002;Tu et al, 2009;Kikuta et al, 2015).…”