Increase In Intracellular Ca Levels Research Articles

Arsenic and fluoride induce neural progenitor cell apoptosis

The aim of the present study is to determine the effect of inorganic arsenic (As) and its metabolites on the viability of the neural progenitor cell (NPC) line C17.2, in order to evaluate cellular mechanisms involved in As developmental neurotoxicity. Moreover, we analyzed the effects of the coexposure to As and fluoride (F), a situation to which some populations are commonly exposed. Our results show that NPCs are not susceptible to pentavalent As species [arsenate, monomethylarsonic acid, and dimethylarsinic acid] and F alone. However, the trivalent metabolites of arsenate [arsenite, monomethylarsonous acid, and dimethylarsinous acid] are toxic at concentrations below 1 mg/l, and this susceptibility increases when there is coexposure with F (≥5 mg/l). Arsenite triggers apoptosis after 24 h of exposure, whereas monomethylarsonous acid produces necrosis at very short times (2 h). Arsenite leads to an increase in intracellular Ca levels and generation of reactive oxygen species, which may cause a decrease in mitochondrial transmembrane potential, release of cytochrome c, and consequent activation of caspases. A slight activation of calpain also takes place, which might favor activation of the mitochondrial pathway or might activate other pathways. The treatment with some antioxidants such as quercetin and α-tocopherol shows only a partial reduction of the cytotoxicity.

Phosphatidylinositol 3,5 bisphosphate increases contractility and intracellular calcium in cardiac muscle by directly activating the cardiac ryanodine receptor.

We have previously reported that treatment of left ventricular cardiac muscle strips with phosphatidylinositol 3,5 bisphosphate (PI(3,5)P2) during field stimulation enhanced the magnitude of isometric force, the rate of force development, and the area associated with the contractile waveforms. In addition, PI(3,5)P2 caused an increase in intracellular calcium (Ca) in cardiac myocytes. These data suggested that PI(3,5)P2 increased contractile force by promoting extracellular Ca entry or by facilitating intracellular Ca release. To elucidate the mechanism responsible for the effects of PI(3,5) on intracellular Ca, we have performed ratiometric Ca imaging in isolated adult mouse cardiac myocytes. We have found that PI(3,5)P2 induced a dramatic increase in intracellular Ca levels, which was inhibited by preincubation with ryanodine. To confirm that PI(3,5)P2 was acting on RyR2 we performed electrophysiological and biochemical studies. PI(3,5)P2 increased [3H]ryanodine binding and this effect was prevented by preincubation with an antibody against PI(3,5)P2. Furthermore, single RyR2 channels reconstituted in lipid bilayers were activated by PI(3,5)P2 in a dose‐dependent manner, indicating that PI(3,5)P2 binds directly to RyR2. We provide inaugural evidence that PI(3,5)P2 regulates cardiac contractility via modulation of intracellular Ca by direct binding and activation of the RyR2 channel.

The effects of phosphatidylinositol 3,5‐bisphosphate on cardiac muscle

The downstream product of phosphatidylinositol 4,5‐bisphosphate (PI(4,5)P2), inositol 1,4,5‐trisphosphate (IP3), is known to induce calcium (Ca) release from the sarcoplasmic reticulum and elicit alterations in contraction of the heart and arrhythmias. What has not been studied is the effects of other phosphoinositides (PIs) such as phosphatidylinositol 3,5‐bisphosphate (PI(3,5)P2) and phosphatidylinositol 3‐phosphate (PI(3)P) on the heart. A striated muscle specific phosphatase (MIP/MTMR14) dephosphorylates PI(3,5)P2, and is present in skeletal and cardiac muscle. MIP knockout animals display reduced exercise performance, providing a strong rationale that PI(3,5)P2 may be involved in heart function. We tested 0.5 µM PI(3,5)P2, PI(4,5)P2, and PI(3)P on left ventricular muscle strips from adult mice paced at 1 Hz. All PIs tested induced an increase in the magnitude of the twitch‐force of the left ventricle. PI(3,5)P2 was also applied to single isolated cardiac myocytes and induced an increase in intracellular Ca levels and altered spontaneous Ca waves. While the mechanism of these actions remains to be determined, these data suggest that PI(3,5)P2, PI(4,5)P2, and PI(3)P may play a role in altering cardiac function. It will be essential to determine the potential role of this novel signaling mechanism in heart‐related diseases where Ca homeostasis is known to be modified.