On 2016 Aug 30, Olga Krizanova commented:

We are aware that there are some papers showing ineffectivity of Xestospongin C on IP3 receptors. Nevertheless, Xest is a widely accepted inhibitor of IP3 receptors (IP3R), as documented by majority IP3R papers and also by companies selling this product (e.g. Sigma-Aldrich, Cayman Chemical, Abcam, etc.). Since Xest also inhibits voltage-dependent Ca2+ and K+ currents at concentrations similar to those which inhibit the IP3R, it can be regarded as a selective blocker of the IP3R in permeabilized cells. Cell type used in experiments might be of a special importance. In our paper we observed the effect of Xest on IP3R1 on four different cell lines -A2780, SKOV3, Bowes and MDA-MB-231. Moreover, we verified results observed by Xest by another IP3R blocker -2-APB and also by IP3R1 silencing. All these results imply that Xest acts as IP3R inhibitor. Recently, paper with more specific Xestospongin B was published, but unfortunately, this compound is not yet commercially available.

On 2016 Aug 22, Darren Boehning commented:

Xestospongin C (Xest) does not inhibit IP3R channels. See PMID: 24628114 PMCID: PMC4080982 DOI: 10.1111/bph.12685 There are other well-documented examples in the literature.

On 2016 Aug 22, Darren Boehning commented:

Xestospongin C (Xest) does not inhibit IP3R channels. See PMID: 24628114 PMCID: PMC4080982 DOI: 10.1111/bph.12685 There are other well-documented examples in the literature.

On 2016 Aug 30, Olga Krizanova commented:

We are aware that there are some papers showing ineffectivity of Xestospongin C on IP3 receptors. Nevertheless, Xest is a widely accepted inhibitor of IP3 receptors (IP3R), as documented by majority IP3R papers and also by companies selling this product (e.g. Sigma-Aldrich, Cayman Chemical, Abcam, etc.). Since Xest also inhibits voltage-dependent Ca2+ and K+ currents at concentrations similar to those which inhibit the IP3R, it can be regarded as a selective blocker of the IP3R in permeabilized cells. Cell type used in experiments might be of a special importance. In our paper we observed the effect of Xest on IP3R1 on four different cell lines -A2780, SKOV3, Bowes and MDA-MB-231. Moreover, we verified results observed by Xest by another IP3R blocker -2-APB and also by IP3R1 silencing. All these results imply that Xest acts as IP3R inhibitor. Recently, paper with more specific Xestospongin B was published, but unfortunately, this compound is not yet commercially available.