Decavanadate displaces inositol 1,4,5-trisphosphate (IP3) from its receptor and inhibits IP3 induced Ca2+ release in permeabilized pancreatic acinar cells

Abstract

-Inositol 1,4,5-trisphosphate (IP3) induced Ca 2 + release in digitonin permeabllized rat pancreatic acinar cells is specifically inhibited by decavanadate. The ca 2 + release induced with 0.18 flM IP3 is half maximally inhibited with approximately 5 flM decavanadate. Complete inhibition is achieved with around 20 flM decavanadate. Removal of decavanadate from the permeabilized cells fully restores sensitivity towards IP3, indicating the reversibility of the inhibition. Oligovanadate, which inhibits A TP dependent ca 2 + up1ake into intracellular stores, does not influence IP3 induced ca 2 + release. In order to reveal the mechanism underlying the effects of the different vanadate species, binding of IP3 to the same cellular preparations was investigated. We found that binding of IP3 to a high affinity receptor site (I<d approx. 1.2 nM) could be abolished by decavanadate but not by oligovanadate. With 0.5 f.1M decavanadate, IP3 binding was half maximally inhibited. A similar potency of decavanadate was also found with adrenal cortex microsomes which bind IP3 with the same affinity (Kd approx. 1.4 nM) as permeabilized pancreatic acinar cells. Labelled IP3 was displaced from these subcellular membranes with similar kinetics by unlabelled IP3 and decavanadate. The data suggest that the inhibitory action of decavanadate on IP3 induced Ca 2 + release is a consequence of its effect on binding of IP3 to its receptor.Intracellular inositol 1,4,5-trisphosphate (IP3), latter was shown for the fIrst time with fOImed at the plasma membrane by the hydrolysis of pelTIleabilized rat pancreatic acinar cells [2] and was phosphatidylinositol-4,5-bisphosphate, causes the subsequently confltmed by innumerable release of Ca 2 + from intracellular stores [1]. The investigations in a variety of cells. Our knowled~e conceming the mechanism of the IP3 induced Ca + release is still limited although the primary structure of the IP3 receptor has been detetmined [3,4]. A useful tool to characterize the IP3 receptor is heparin. It inhibits binding of IP3 to its receptor [5][6][7] and IP3 induced cl+ release [8][9][10]. The

Pharmacological Regulators of Intracellular Calcium Release Channels

“…The action of decavanadate can be overcome by increasing the concentration of IP 3 , suggesting competition for the IP 3 binding site [115], an observation that is confirmed by radioligand binding experiments where decavanadate inhibits the specific binding of [ 3 H]IP 3 to IP 3 R with low micromolar affinity [117]. Such activity appears unique to decavanadate as other vanadate compounds, such as orthovanadate and oligovanadate, have no effect on IP 3 binding or IP 3 -induced Ca 2+ release, even at high concentrations [116][117]. Likewise, decavanadate has no effect on SERCA-driven Ca 2+ uptake, whereas oligovanadate is a potent inhibitor of this Ca 2+ pump.…”

“…The polyoxoanion, decavanadate, is a well known inhibitor of IP 3 -induced Ca 2+ release in a variety of cell types with an IC 50 of ~5 M [115][116]. The action of decavanadate can be overcome by increasing the concentration of IP 3 , suggesting competition for the IP 3 binding site [115], an observation that is confirmed by radioligand binding experiments where decavanadate inhibits the specific binding of [ 3 H]IP 3 to IP 3 R with low micromolar affinity [117].…”

Decavanadate (V10O286-) and oxovanadates: Oxometalates with many biological activities

“…In vitro experiments showed that V 10 inhibits myosin ATPase, SR calcium ATPase, and SR calcium release induced by the second messenger inositol triphosphate (IP3) [51,98,134]. Importantly, decavanadate inhibits both the contractile system and the regulation of muscle contraction.…”

Vanadium and proteins: Uptake, transport, structure, activity and function

“…Myosin is a protein that plays a pivotal role in ATPdriven Ca 2+ -dependent muscle contraction and it was found that docking of decavanadate stabilizes it against break-down to monovanadate(V). In vitro experiments showed that V 10 inhibits myosin ATPase, SR Ca 2+ -ATPase, and SR Ca 2+ release induced by the second messenger inositol triphosphate (IP3) [364] [365] [366]. Moreover, decavanadate inhibits both the contractile system and the regulation of muscle contraction.…”