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Inositol hexakisphosphate binding sites in rat heart and brain
K G Rowley1, A L Gundlach, M Cincotta
1University of Melbourne, Department of Medicine, Austin and Repatriation Medical Centre, Heidelberg, Victoria, Australia.
British Journal of Pharmacology
|August 1, 1996
Summary
This study identifies specific binding sites for inositol hexakisphosphate (InsP6) in rat heart tissue, revealing its potential role in cardiac function. Further research is needed to clarify the functional significance of InsP6 and its receptors in the heart.
Area of Science:
- Cardiovascular Physiology
- Cell Signaling
- Biochemistry
Background:
- Cardiac alpha 1-adrenoceptors stimulate the production of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) and inositol hexakisphosphate (InsP6).
- The function of Ins(1,4,5)P3 and its receptors in cardiac tissue is understood, but the role of the InsP6-InsP6 receptor system remains unclear.
- Previous research suggests potential links between InsP6 and cardiac mitochondrial Ca2+ regulation.
Purpose of the Study:
- To investigate the characteristics and regional distribution of [3H]-InsP6 binding sites in rat heart.
- To compare the binding affinities of various inositol polyphosphates for [3H]-InsP6 and [3H]-Ins(1,4,5)P3 binding sites in cardiac and brain tissues.
- To evaluate the specificity of Ins(1,4,5)PS3 as a ligand for InsP6 and Ins(1,4,5)P3 receptors.
Main Methods:
- Quantitative autoradiography was employed to analyze [3H]-InsP6 binding in rat heart sections.
- Binding affinities of different inositol phosphates were assessed using competition assays.
- The inhibitory effects of Ins(1,4,5)PS3 on [3H]-InsP6 and [3H]-Ins(1,4,5)P3 binding were determined.
Main Results:
- High-affinity [3H]-InsP6 binding sites were identified across various regions of the rat heart, with distinct dissociation constants (KD) and maximal binding capacities (Bmax).
- Inositol phosphates exhibited a specific order of potency in inhibiting [3H]-InsP6 binding, confirming the presence of an InsP6 binding site.
- Ins(1,4,5)PS3 demonstrated potent inhibition of [3H]-InsP6 binding in the heart and comparable inhibition of [3H]-Ins(1,4,5)P3 binding in the brain, indicating a lack of specificity.
Conclusions:
- The study confirms the presence of specific, high-affinity InsP6 binding sites within the rat heart.
- The findings suggest that InsP6 may play a distinct functional role in cardiac tissue, separate from Ins(1,4,5)P3.
- Further investigation is warranted to elucidate the precise physiological functions of InsP6 and its associated receptors in cardiac cells, particularly concerning calcium regulation.