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Inhibition of the Inositol Trisphosphate Receptor of Mouse Eggs and A7r5 Cells by KN-93 via a Mechanism Unrelated to Ca2+/calmodulin-dependent Protein Kinase II Antagonism

Inhibition of the Inositol Trisphosphate Receptor of Mouse Eggs and A7r5 Cells by KN-93 via a Mechanism Unrelated to Ca2+/calmodulin-dependent Protein Kinase II Antagonism

Jeremy T Smyth, Allison L Abbott, Bora Lee, Ilse Sienaert, Nael Nadif Kasri, Humbert De Smedt, Tom Ducibella, Ludwig Missiaen, Jan B Parys, Rafael A Fissore

J Biol Chem. 2002 Sep 20;277(38):35061-70.

PMID: 12121980

Abstract:

KN-93, a Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibitor, concentration-dependently and reversibly inhibited inositol 1,4,5-trisphosphate receptor (IP(3)R)-mediated [Ca(2+)](i) signaling in mouse eggs and permeabilized A7r5 smooth muscle cells, two cell types predominantly expressing type-1 IP(3)R (IP(3)R-1). KN-92, an inactive analog, was ineffective. The inhibitory action of KN-93 on Ca(2+) signaling depended neither on effects on IP(3) metabolism nor on the filling grade of Ca(2+) stores, suggesting a direct action on the IP(3)R. Inhibition was independent of CaMKII, since in identical conditions other CaMKII inhibitors (KN-62, peptide 281-309, and autocamtide-related inhibitory peptide) were ineffective and since CaMKII activation was precluded in permeabilized cells. Moreover, KN-93 was most effective in the absence of Ca(2+). Analysis of Ca(2+) release in A7r5 cells at varying [IP(3)], of IP(3)R-1 degradation in eggs, and of [(3)H]IP(3) binding in Sf9 microsomes all indicated that KN-93 did not affect IP(3) binding. Comparison of the inhibition of Ca(2+) release and of [(3)H]IP(3) binding by KN-93 and calmodulin (CaM), either separately or combined, was compatible with a specific interaction of KN-93 with a CaM-binding site on IP(3)R-1. This was also consistent with the much smaller effect of KN-93 in permeabilized 16HBE14o(-) cells that predominantly express type 3 IP(3)R, which lacks the high affinity CaM-binding site. These findings indicate that KN-93 inhibits IP(3)R-1 directly and may therefore be a useful tool in the study of IP(3)R functional regulation.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
IAR42415239	Ca2+/Calmodulin Kinase II Inhibitor 281-309			Price

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