Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “IP3R”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

7 recordsLinked to original sources
PubMed1992

Inositol 1,4,5-trisphosphate receptors. Localization in epithelial tissue.

Using a polyclonal antiserum raised against the inositol 1,4,5-trisphosphate receptor (IP3R) purified from rat cerebellum, we examined the subcellular distribution of IP3R in canine pancreatic homogenates. IP3R was present primarily in a smooth microsomal fraction (low density), a (high density) rough microsomal (RM) fraction previously shown to consist of highly purified rough endoplasmic reticulum (RER) vesicles, and, to a much lesser extent, in an intermediate density microsomal fraction which did not contain markers for RER or plasma membrane. When the RM fraction was subjected to isopycnic centrifugation on sucrose gradients, IP3R equilibrated at high sucrose densities. When ribosomes were extracted from the RM fraction by treatment with puromycin/high salt, IP3R equilibrated at considerably lighter sucrose densities. This shift in density indicated that IP3R which was present in the RM fraction is associated with the RER. Because of a significant amount of IP3R fractionating into the smooth microsomal fraction (which contains plasma membrane, among other "smooth" membranes) and a considerable amount of IP3R present in the nuclear pellet which is also enriched in plasma membrane, we examined the possibility that IP3R may be present in plasma membrane. Further subfractionation of a crude plasma membrane pellet from rat liver revealed that IP3R coenriched with a plasma membrane marker and strongly suggested an association of IP3R with plasma membrane. The issue of why the same receptor is found in multiple biochemically and morphologically distinct membrane fractions is discussed in terms of the possibility of RER subcompartmentalization and IP3R subtypes. The fractionation pattern of IP3R in pancreas is significantly different from that previously reported for calcium (Ca2+)-binding proteins and an intracellular Ca-ATPase (Nigam, S. K. and Towers, T. (1990) J. Cell Biol. 111, 197-200), raising questions as to links between these latter proteins and IP3 sensitive Ca2+ pools. Nevertheless, although the fractionation patterns are different, all of these proteins are clearly associated with the RER.

Animals↗
PubMed1992

Three additional inositol 1,4,5-trisphosphate receptors: molecular cloning and differential localization in brain and peripheral tissues.

Three inositol 1,4,5-trisphosphate receptor (IP3R) cDNAs, designated IP3R-II, -III, and -IV, were cloned from a mouse placenta cDNA library. All three display strong homology in membrane-spanning domains M7 and M8 to the originally cloned cerebellar IP3R-I, with divergences predominantly in cytoplasmic domains. Levels of mRNA for the three additional IP3Rs in general are substantially lower than for IP3R-I, though in the gastrointestinal tract the levels of IP3R-III may be comparable to IP3R-I. Cerebellar Purkinje cells express at least two and possibly three distinct IP3Rs, suggesting heterogeneity of IP3 action within a single cell.

Amino Acid Sequence↗
PubMed1992

Plasma membrane inositol 1,4,5-trisphosphate receptor of lymphocytes: selective enrichment in sialic acid and unique binding specificity.

The inositol 1,4,5-trisphosphate receptor (IP3R) associated with plasma membranes of lymphocytes differs in terminal sugar content and binding specificity from the cerebellar receptor, which is localized to endoplasmic reticulum. Lectin column chromatography reveals that 30% of IP3R in the thymus contains sialic acid, reflecting a plasma membrane association, in contrast to 5% of cerebellar IP3R. IP3R in thymus and plasma membrane fractions of Jurkat lymphocytes differs from IP3R of Jurkat microsomes and cerebellum in inositol phosphate specificity. The plasma membrane IP3R has lower affinity for IP3 but higher affinity for inositol 1,3,4,5-tetrakisphosphate, which may reflect a unique regulation of calcium at the plasma membrane by inositol phosphates.

Animals↗
PubMed2026

Intermembrane coupling between Bcl-xL and the IP3 receptor supports local Ca2+ transfer at ER-mitochondrial contacts.

Bcl-xL, an anti-apoptotic Bcl-2 family protein, engages laterally with Bak/Bax in the outer mitochondrial membrane (OMM) to inhibit apoptosis and interacts with the IP3 receptor Ca2+ channels (IP3Rs) in the endoplasmic reticulum (ER) membrane to control Ca2+ release. It is unknown if OMM-localized Bcl-xL can also interact in trans with IP3Rs at ER-mitochondrial contacts to form a tethering complex that supports IP3R-mediated local Ca2+ transfer from ER to mitochondria. We establish that IP3R-mitochondria Ca2+ signal propagation depends on Bcl-xL. By targeting Bcl-xL specifically to different subcellular compartments, we find that OMM-localized Bcl-xL increases the efficacy of ER-mitochondrial Ca2+ transfer without changing ER Ca2+ release, despite attenuating mitochondrial Ca2+ uptake. We find interaction between Bcl-xL and each IP3R isoform occurring at the mitochondria and a complex formed by OMM-localized Bcl-xL and IP3Rs. OMM Bcl-xL interacts with IP3Rs in trans at ER-mitochondrial contacts to optimize local Ca2+ signal propagation into the mitochondria.

Bcl-xL↗
PubMed1992

Calcium channels expressed in vascular smooth muscle.

BACKGROUND: Regulation of intracellular calcium levels is known to activate signal transduction pathways, leading to well-defined patterns of gene expression. METHODS AND RESULTS: Among the calcium-responsive genes are those involved in the growth and proliferative responses of vascular smooth muscle cells. Cytoplasmic calcium also plays a role in activating a host of cellular functions including smooth muscle contraction and growth factor release. Calcium channels participate in the regulation of cytoplasmic calcium concentration in vascular smooth muscle. Two major classes of calcium channels are expressed in vascular smooth muscle cells: voltage-dependent calcium channels on the plasmalemma and intracellular calcium release channels on the endoplasmic reticulum. The voltage-dependent calcium channel is activated by depolarization of the plasmalemma. This calcium channel belongs to the super gene family that includes the voltage-dependent potassium and sodium channels. These three cation channels share a common transmembrane topography. The major intracellular calcium release channel in vascular smooth muscle is the inositol 1,4,5-trisphosphate receptor (IP3R) on the endoplasmic reticulum. The IP3R is activated by IP3, a second messenger generated at the plasmalemma, which mediates numerous cellular responses including smooth muscle contraction. Also present in smooth muscle cells is the ryanodine receptor (RYR)/calcium release channel of the sarcoplasmic reticulum. CONCLUSIONS: The RYR is the major intracellular calcium release channel of striated muscles and is expressed in relatively low levels in vascular smooth muscle. The IP3R and RYR are members of a gene family encoding intracellular calcium release channels with characteristic fourfold symmetric structures.

Amino Acid Sequence↗
PubMed1991

The properties of intracellular calcium stores in cultured rat cerebellar neurons.

Cerebellar Purkinje neurons contain a remarkable array of cellular components potentially concerned with regulation of the free cytoplasmic Ca2+ concentration, [Ca2+]i. These include high concentrations of Ca(2+)-binding proteins, inositol 1,4,5-triphosphate receptors (IP3R), and ryanodine receptors (RyR). The latter two molecules are thought to be associated with intracellular Ca2+ stores. We have examined the properties of such stores in cultured rat cerebellar neurons taken from 16 d rat embryos. In this system, about half of the neurons could be identified as Purkinje-like cells, as indicated by staining for the Ca(2+)-binding protein calbindin D-28k, as well as for IP3R and RyR. In double immunofluorescent staining, the IP3R and RyR immunoreactivity primarily colocalized with the staining for calbindin. The cells responded to glutamate, kainate, and quisqualate with large increases in the somatic [Ca2+]i but failed to respond directly to NMDA (10-50 microM). Furthermore, the neurons expressed active membrane conductances, repetitive action potential firing, and spontaneous firing patterns similar to those reported for cerebellar Purkinje neurons in vivo. Action potential firing produced changes in somatic [Ca2+]i that were quite small or absent in most cells. However, blocking spike repolarization with tetraethylammonium (5 mM) produced substantial transient elevations in somatic [Ca2+]i, suggesting the expression of some Ca2+ channels in the somatic membrane. Caffeine (10 mM) released Ca2+ from intracellular stores in about one-half of the cultured neurons. This effect could be repeated if the stores were first reloaded by a depolarization-induced elevation in [Ca2+]i. The effects of caffeine were reduced by prolonged application of ryanodine (10 microM). We were also able to demonstrate that the caffeine-sensitive Ca2+ stores could regulate electrophysiological events in some cells, altering patterns of spontaneous activity. Furthermore, in the presence of caffeine, [Ca2+]i signals induced by an evoked spike train were larger and accompanied by long-lasting after hyperpolarizations. We conclude that in addition to providing a releasable pool of Ca2+, the caffeine-sensitive stores also influence cellular events by their contribution to Ca2+ buffering.

Animals↗
PubMed2026

Signaling mechanisms of vasopressin/oxytocin-type neuropeptide-induced muscle contraction in the sea cucumber Apostichopus japonicus.

The myoregulatory action of vasopressin/oxytocin (VP/OT)-type neuropeptides is evolutionarily conserved across Bilateria. In vertebrates, the signaling cascades involved have been comprehensively characterized in several muscle types, including uterine and gastrointestinal smooth muscles. VP/OT-type neuropeptide-induced muscle contraction or relaxation has been reported in a variety of invertebrates, but the downstream signaling pathways responsible for these effects have yet to be elucidated. Here, using heterologous cell systems and in vitro pharmacological experiments, we investigated the signaling pathways underlying VP/OT-type neuropeptide (holotocin) induced contraction of the longitudinal muscle of the body wall (LMBW) in the sea cucumber Apostichopus japonicus (phylum Echinodermata), a deuterostome invertebrate. Holotocin-induced contraction of the LMBW comprised two distinct phases: an initial rapid phasic contraction followed by a sustained tonic contraction. Pharmacological experiments revealed that upon binding to its receptor AjHOR, holotocin activates a Gαq-dependent pathway, leading to phospholipase C (PLC) activation and subsequent hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 triggers Ca2+ release from intracellular Ca2+ stores via IP₃ receptors (IP3R), but depletion of intracellular Ca2+ does not activate store-operated Ca2+ entry (SOCE). DAG activates protein kinase C (PKC), which may modulate the activity of ion channels in the plasma membrane, resulting in membrane depolarization, opening of voltage-gated Ca2+ channels (VGCCs), and subsequent influx of extracellular Ca2+. Overall, this study reveals similarities and differences in the signaling pathways mediating smooth muscle contraction in invertebrates and vertebrates, providing new insights into the evolution of these mechanisms across the Bilateria.

Ca(2+)↗