Getting old without type 2 IP3 receptors

Gq-protein coupled receptor (GPCR) stimulation promotes PLC function, generating diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). The latter may promote Ca2+ translocation from intracellular stores altering Ca2+ homeostasis in cardiomyocytes. The aim of this study was to establish whether GPCR agonists enhance IP3 receptor (IP3R) activity, affecting the electromechanical properties of LV myocytes. For this purpose, the functional responses of myocytes to GPCR agonists ATP or ET-1 were established. In field-stimulated cells, GPCR activators increased diastolic Ca2+, transient amplitude, and contractility; extra-systolic Ca2+ releases and aftercontractions were promoted. These responses were prevented by inhibition of PLC, or blockade of IP3Rs. Since DAG promotes PKC activity, the effects of GPCR stimulation were tested in the presence of the PKC inhibitor chelerythrine. This compound failed to abrogate the effects of ATP and ET-1, indicating that PKC-independent pathways play a critical role in mediating the observed cellular responses to GPCR stimulation. Additionally, an AAV9 vector carrying EGFP and sh-RNA targeting IP3R type-2 was employed in vivo to downregulate IP3Rs. GPCRs activation failed to increase Ca2+ transients and to induce extra-systolic Ca2+ elevations in EGFP-positive myocytes. Conversely, these responses were preserved in EGFP-negative cells. In patch-clamped myocytes, changes in Ca2+ transient properties following GPCR activation were accompanied by a decrease in resting potential, action potential (AP) prolongation, and emergence of arrhythmic events. Similar electrical disturbances were detected by direct activation of IP3R with IP3 dialysis, or by enhancing the affinity of the receptors to its ligand, with thimerosal. To establish whether Ca2+ mobilized from the sarcoplasmic reticulum (SR) to the cytoplasm via IP3Rs was responsible for the electrical alterations caused by GPCR agonists, experiments were performed in which SR Ca2+ was depleted, or cytosolic Ca2+ was buffered. Under these conditions, ATP and ET-1 failed to prolong the AP and to induce arrhythmias. In conclusion, the GPCR/IP3R axis regulates Ca2+ homeostasis, contractile performance and the electrical stability of LV myocytes.

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Type 2 IP3 receptors are involved in uranyl acetate induced apoptosis in HEK 293 cells

Toxicology ◽

10.1016/j.tox.2009.05.006 ◽

2009 ◽

Vol 262 (1) ◽

pp. 73-79 ◽

Cited By ~ 10

Author(s):

Juraj Kopacek ◽

Karol Ondrias ◽

Barbora Sedlakova ◽

Jana Tomaskova ◽

Lucia Zahradnikova ◽

...

Keyword(s):

Uranyl Acetate ◽

Ip3 Receptors ◽

Hek 293 ◽

Hek 293 Cells ◽

293 Cells ◽

Induced Apoptosis

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Expression of mRNAs for different types of IP3 receptors in rat kidneys

AJP Renal Physiology ◽

10.1152/ajprenal.1995.268.6.f1046 ◽

1995 ◽

Vol 268 (6) ◽

pp. F1046-F1052 ◽

Cited By ~ 2

Author(s):

T. Yang ◽

Y. Terada ◽

H. Nonoguchi ◽

K. Tomita ◽

F. Marumo

Keyword(s):

Collecting Duct ◽

Rat Kidney ◽

Ip3 Receptors ◽

Ip3 Receptor ◽

Receptor Mrna ◽

Collecting Ducts ◽

Different Types ◽

Medullary Collecting Duct

Cloning studies have extensively characterized two types of inositol 1,4,5-trisphosphate (IP3) receptors from the rat. An IP3 receptor from the cerebellum is referred to as type 1, and a second, recently described, receptor is referred to as the type 2 IP3 receptor. The significance of different types of IP3 receptors, especially in vivo in the kidney, is not fully understood. We investigated the localization of mRNAs encoding these two types of IP3 receptors in microdissected nephron segments of rats using reverse transcription and polymerase chain reaction (RT-PCR) followed by Southern blot analysis. Type 1 IP3 receptor mRNA displayed a widespread, although not uniform, distribution along the nephron. In contrast, type 2 IP3 receptor mRNA was confined almost exclusively to collecting ducts, suggesting specific expression of type 2 IP3 receptor in collecting ducts. We then detected mRNAs for the two types of IP3 receptors in collecting ducts in dehydrated rats. Dehydration downregulated type 2 IP3 receptor mRNA in cortical collecting duct, outer medullary collecting duct, and the initial part of inner medullary collecting duct (IMCD), but not in the terminal part of IMCD. It had no effect on type 1 IP3 receptor mRNA expression in collecting ducts. We propose that different types of IP3 receptors may have different functions in the rat kidney. the initial part of inner medullary collecting duct (IMCD), but not in the terminal part of IMCD. It had no effect on type 1 IP3 receptor mRNA expression in collecting ducts. We propose that different types of IP3 receptors may have different functions in the rat kidney.

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Type 2 and type 3 inositol 1,4,5-trisphosphate (IP3) receptors promote the differentiation of granule cell precursors in the postnatal cerebellum

Journal of Neurochemistry ◽

10.1111/j.1471-4159.2008.05221.x ◽

2008 ◽

Vol 105 (4) ◽

pp. 1153-1164 ◽

Cited By ~ 8

Author(s):

Akira Futatsugi ◽

Etsuko Ebisui ◽

Katsuhiko Mikoshiba

Keyword(s):

Granule Cell ◽

Ip3 Receptors ◽

Inositol 1,4,5 Trisphosphate ◽

Type 3 ◽

Granule Cell Precursors

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Decreased olfactory mucus secretion and nasal abnormality in mice lacking type 2 and type 3 IP3 receptors

European Journal of Neuroscience ◽

10.1111/j.1460-9568.2008.06240.x ◽

2008 ◽

Vol 27 (10) ◽

pp. 2665-2675 ◽

Cited By ~ 23

Author(s):

Nanaho Fukuda ◽

Mika Shirasu ◽

Koji Sato ◽

Etsuko Ebisui ◽

Kazushige Touhara ◽

...

Keyword(s):

Mucus Secretion ◽

Ip3 Receptors ◽

Type 3

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Selective recognition of inositol phosphates by subtypes of the inositol trisphosphate receptor

Biochemical Journal ◽

10.1042/bj3550059 ◽

2001 ◽

Vol 355 (1) ◽

pp. 59-69 ◽

Cited By ~ 20

Author(s):

Edmund P. NEROU ◽

Andrew M. RILEY ◽

Barry V. L. POTTER ◽

Colin W. TAYLOR

Keyword(s):

Hydroxy Group ◽

Inositol Phosphates ◽

Inositol Trisphosphate ◽

Receptor Subtypes ◽

Ip3 Receptors ◽

Ip3 Receptor ◽

Subtype Selectivity ◽

Type 3

Synthetic analogues of inositol trisphosphate (IP3), all of which included structures equivalent to the 4,5-bisphosphate of (1,4,5)IP3, were used to probe the recognition properties of rat full-length type 1, 2 and 3 IP3 receptors expressed in insect Spodoptera frugiperda 9 cells. Using equilibrium competition binding with [3H](1,4,5)IP3 in Ca2+-free cytosol-like medium, the relative affinities of the receptor subtypes for (1,4,5)IP3 were type 3 (Kd = 11±2nM)>type 2 (Kd = 17±2nM) > type 1 (Kd = 24±4nM). (1,4,5)IP3 binding was reversibly stimulated by increased pH, but the subtypes differed in their sensitivity to pH (type 1 > type 2>type 3). For all three subtypes, the equatorial 6-hydroxy group of (1,4,5)IP3 was essential for high-affinity binding, the equatorial 3-hydroxy group significantly improved affinity, and the axial 2-hydroxy group was insignificant; a 1-phosphate (or in its absence, a 2-phosphate) improved binding affinity. The subtypes differed in the extents to which they tolerated inversion of the 3-hydroxy group of (1,4,5)IP3 (type 1>type 2>type 3), and this probably accounts for the selectivity of (1,4,6)IP3 for type 1 receptors. They also differed in their tolerance of inversion, removal or substitution (by phosphate) of the 2-hydroxy group (types 2 and 3>type 1), hence the selectivity of (1,2,4,5)IP4 for type 2 and 3 receptors. Removal of the 3-hydroxy group or its replacement by fluorine or CH2OH was best tolerated by type 3 receptors, and accounts for the selectivity of 3-deoxy(1,4,5)IP3 for type 3 receptors. Our results provide the first systematic analysis of the recognition properties of IP3 receptor subtypes and have identified the 2- and 3-positions of (1,4,5)IP3 as key determinants of subtype selectivity.

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Selective coupling of type 6 adenylyl cyclase with type 2 IP3 receptors mediates direct sensitization of IP3 receptors by cAMP

The Journal of Cell Biology ◽

10.1083/jcb.200803172 ◽

2008 ◽

Vol 183 (2) ◽

pp. 297-311 ◽

Cited By ~ 74

Author(s):

Stephen C. Tovey ◽

Skarlatos G. Dedos ◽

Emily J.A. Taylor ◽

Jarrod E. Church ◽

Colin W. Taylor

Keyword(s):

Adenylyl Cyclase ◽

Spatial Organization ◽

Cyclic Adenosine Monophosphate ◽

Adenosine Monophosphate ◽

Ip3 Receptors ◽

Human Embryonic Kidney Cells ◽

Intracellular Messengers ◽

Localized Delivery ◽

Interfering Rna

Interactions between cyclic adenosine monophosphate (cAMP) and Ca2+ are widespread, and for both intracellular messengers, their spatial organization is important. Parathyroid hormone (PTH) stimulates formation of cAMP and sensitizes inositol 1,4,5-trisphosphate receptors (IP3R) to IP3. We show that PTH communicates with IP3R via “cAMP junctions” that allow local delivery of a supramaximal concentration of cAMP to IP3R, directly increasing their sensitivity to IP3. These junctions are robust binary switches that are digitally recruited by increasing concentrations of PTH. Human embryonic kidney cells express several isoforms of adenylyl cyclase (AC) and IP3R, but IP3R2 and AC6 are specifically associated, and inhibition of AC6 or IP3R2 expression by small interfering RNA selectively attenuates potentiation of Ca2+ signals by PTH. We define two modes of cAMP signaling: binary, where cAMP passes directly from AC6 to IP3R2; and analogue, where local gradients of cAMP concentration regulate cAMP effectors more remote from AC. Binary signaling requires localized delivery of cAMP, whereas analogue signaling is more dependent on localized cAMP degradation.

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