Tissue distribution of ryanodine receptor isoforms and alleles determined by reverse transcription polymerase chain reaction

Expression of the ryanodine receptor isoforms in immune cells

Ryanodine receptor (RYR) is a Ca(2+) channel that mediates Ca(2+) release from intracellular stores. We have used RT-PCR analysis and examined its expression in primary peripheral mononuclear cells (PBMCs) and in 164 hemopoietic cell lines. In PBMCs, type 1 RYR (RYR1) was expressed in CD19(+) B lymphocytes, but less frequently in CD3(+) T lymphocytes and in CD14(+) monocytes. Type 2 RYR (RYR2) was mainly detected in CD3(+) T cells. Induction of RYR1 and/or RYR2 mRNA was found after treatment with stromal cell-derived factor 1, macrophage-inflammatory protein-1alpha (MIP1alpha) or TGF-beta. Type 3 RYR (RYR3) was not detected in PBMCs. Many hemopoietic cell lines expressed not only RYR1 or RYR2 but also RYR3. The expression of the isoforms was not associated with specific cell lineage. We showed that the RYR-stimulating agent 4-chloro-m-cresol (4CmC) induced Ca(2+) release and thereby confirmed functional expression of the RYR in the cell lines expressing RYR mRNA. Moreover, concordant induction of RYR mRNA with Ca(2+) channel function was found in Jurkat T cells. In untreated Jurkat T cells, 4CmC (>1 mM) had no effect on Ca(2+) release, whereas 4CmC (<400 microM) caused Ca(2+) release after the induction of RYR2 and RYR3 that occurred after treatment with stromal cell-derived factor 1, macrophage-inflammatory protein-1alpha, or TGF-beta. Our results demonstrate expression of all three isoforms of RYR mRNA in hemopoietic cells. Induction of RYRs in response to chemokines and TGF-beta suggests roles in regulating Ca(2+)-mediated cellular responses during the immune response.

Increased expression of isoform 1 of the sarcoplasmic reticulum Ca(2+)-release channel in failing human heart

BACKGROUND

The sarcoplasmic reticulum (SR) Ca(2+)-release channel plays a key role in the excitation-contraction coupling of cardiac myocytes. Because respective alterations have been reported in human heart failure, we investigated isoform expression of the SR Ca(2+)-release channel in human hearts from patients with terminal heart failure (dilated cardiomyopathy [DCM], n=8) and nonfailing organ donors (NF, n=8).

METHODS AND RESULTS

Expression of mRNA of SR Ca(2+)-release channel isoforms in isolated human cardiomyocytes and myocardial tissue was analyzed by reverse-transcription polymerase chain reaction. Protein expression was quantified in myocardial tissue with [(3)H]-ryanodine binding and with Western blots, expressed as densitometric units per microgram of protein (DU), and cellular localization was visualized with immunohistochemistry. We found mRNA expression of isoforms 1, 2, and 3 in cardiomyocytes and myocardial tissue both in NF and DCM. Total SR Ca(2+)-release channel protein expression in NF (B(max) 2.16+/-0.43 pmol/mg protein) and in DCM (B(max) 2.33+/-0.22 pmol/mg protein) myocardium was unchanged. Expression of isoform 1 of the SR Ca(2+)-release channel was significantly (P=0.0037) increased in DCM myocardium (NF 1.97+/-0.25 versus DCM 3.37+/-0.31 DU), whereas protein expression of isoform 2 (NF 14.62+/-0.87 versus DCM 13.52+/-0.43 DU) and isoform 3 (NF 1.39+/-0.13 versus DCM 1.35+/-0.19 DU) was unchanged. All 3 isoforms of the protein could be localized in human ventricular myocytes with fluorescence immunohistochemistry.

CONCLUSIONS

All 3 isoforms of the SR Ca(2+)-release channel were determined in human ventricular cardiomyocytes. Increased expression of isoform 1 of the SR Ca(2+)-release channel could contribute to impaired excitation-contraction coupling in human heart failure.

Dantrolene inhibition of ryanodine receptor Ca2+ release channels. Molecular mechanism and isoform selectivity

As an inhibitor of Ca(2+) release through ryanodine receptor (RYR) channels, the skeletal muscle relaxant dantrolene has proven to be both a valuable experimental probe of intracellular Ca(2+) signaling and a lifesaving treatment for the pharmacogenetic disorder malignant hyperthermia. However, the molecular basis and specificity of the actions of dantrolene on RYR channels have remained in question. Here we utilize [(3)H]ryanodine binding to further investigate the actions of dantrolene on the three mammalian RYR isoforms. The inhibition of the pig skeletal muscle RYR1 by dantrolene (10 microm) was associated with a 3-fold increase in the K(d) of [(3)H]ryanodine binding to sarcoplasmic reticulum (SR) vesicles such that dantrolene effectively reversed the 3-fold decrease in the K(d) for [(3)H]ryanodine binding resulting from the malignant hyperthermia RYR1 Arg(615) --> Cys mutation. Dantrolene inhibition of the RYR1 was dependent on the presence of the adenine nucleotide and calmodulin and reflected a selective decrease in the apparent affinity of RYR1 activation sites for Ca(2+) relative to Mg(2+). In contrast to the RYR1 isoform, the cardiac RYR2 isoform was unaffected by dantrolene, both in native cardiac SR vesicles and when heterologously expressed in HEK-293 cells. By comparison, the RYR3 isoform expressed in HEK-293 cells was significantly inhibited by dantrolene, and the extent of RYR3 inhibition was similar to that displayed by the RYR1 in native SR vesicles. Our results thus indicate that both the RYR1 and the RYR3, but not the RYR2, may be targets for dantrolene inhibition in vivo.

RYR1 and RYR3 have different roles in the assembly of calcium release units of skeletal muscle

Calcium release units (CRUs) are junctions between the sarcoplasmic reticulum (SR) and exterior membranes that mediates excitation contraction (e-c) coupling in muscle cells. In skeletal muscle CRUs contain two isoforms of the sarcoplasmic reticulum Ca(2+)release channel: ryanodine receptors type 1 and type 3 (RyR1 and RyR3). 1B5s are a mouse skeletal muscle cell line that carries a null mutation for RyR1 and does not express either RyR1 or RyR3. These cells develop dyspedic SR/exterior membrane junctions (i.e., dyspedic calcium release units, dCRUs) that contain dihydropyridine receptors (DHPRs) and triadin, two essential components of CRUs, but no RyRs (or feet). Lack of RyRs in turn affects the disposition of DHPRs, which is normally dictated by a linkage to RyR subunits. In the dCRUs of 1B5 cells, DHPRs are neither grouped into tetrads nor aligned in two orthogonal directions. We have explored the structural role of RyR3 in the assembly of CRUs in 1B5 cells independently expressing either RyR1 or RyR3. Either isoform colocalizes with DHPRs and triadin at the cell periphery. Electron microscopy shows that expression of either isoform results in CRUs containing arrays of feet, indicating the ability of both isoforms to be targeted to dCRUs and to assemble in ordered arrays in the absence of the other. However, a significant difference between RyR1- and RyR3-rescued junctions is revealed by freeze fracture. While cells transfected with RyR1 show restoration of DHPR tetrads and DHPR orthogonal alignment indicative of a link to RyRs, those transfected with RyR3 do not. This indicates that RyR3 fails to link to DHPRs in a specific manner. This morphological evidence supports the hypothesis that activation of RyR3 in skeletal muscle cells must be indirect and provides the basis for failure of e-c coupling in muscle cells containing RyR3 but lacking RyR1 (see the accompanying report, ).

Characterization of [(3)H]ryanodine binding sites in mammalian lung

The ryanodine-sensitive calcium channels, also called ryanodine receptors, are intracellular Ca(2+)-release channels that have been shown to bind the neutral plant alkaloid ryanodine with nanomolar affinity. The activity of the skeletal muscle (RyR1), cardiac muscle (RyR2), and brain (RyR3) ryanodine receptor isoforms have been shown to be highly regulated by physiological factors including pH, temperature, and ionic strength; endogenous compounds including Ca(2+), Mg(2+), and adenosine triphosphate (ATP); and pharmacological agents including caffeine, ruthenium red, and neomycin. RyR3 is reportedly expressed in diverse tissues including lung; however, specific [(3)H]ryanodine binding sites in mammalian lung tissue have not been characterized. In this study, hamster lung ryanodine binding proteins were shown to specifically bind [(3)H]ryanodine with an affinity similar to that of RyR isoforms found in other tissues and this binding was shown to be sensitive to Ca(2+) concentration, stimulation by caffeine and spermine, and inhibition by Mg(2+), ruthenium red, and neomycin. The solubilized, intact ryanodine binding protein from hamster lung demonstrated approximately the same 30S sedimentation coefficient as RyR1 and RyR2, but a putative ryanodine receptor subunit from hamster lung was not found to cross-react with antibodies specific for the three known isoforms. We conclude that the hamster lung ryanodine binding protein demonstrates sedimentation and binding characteristics that are similar to those of the known RyR isoforms, but may exhibit antigenic dissimilarity from the typical RyR isoforms found in muscle and brain.

Intracellular Ca(2+) handling in vascular smooth muscle cells is affected by proliferation

Despite intensive interest in the dedifferentiation process of vascular smooth muscle cells, very little data are available on intracellular Ca(2+) signaling. The present study was designed to investigate the evolution of the intracellular Ca(2+) pools when rat aortic smooth muscle cells (RASMCs) proliferate and to define the mechanisms involved in the functional alterations. RASMCs were cultured in different conditions, and [Ca(2+)](i) was measured by use of fura 2. Expression of the sarco(endo)plasmic reticulum Ca(2+) pumps (SERCA2a and SERCA2b), Ca(2+) channels, the ryanodine receptor (RyR), and the inositol trisphosphate receptor (IP3R) was studied by reverse transcription-polymerase chain reaction and immunofluorescence. Antibodies specific for myosin heavy chain isoforms were used as indicators of the differentiation state of the cell, whereas an anti-proliferating cell nuclear antigen antibody was a marker of proliferation. SERCA2a, SERCA2b, RyR3, and IP3R-1 mainly were present in the aorta in situ and in freshly isolated RASMCs. These cells used the 2 types of Ca(2+) channels to release Ca(2+) from a common thapsigargin-sensitive store. Proliferation of RASMCs, induced by serum or by platelet-derived growth factor-BB, resulted in the disappearance of RyR and SERCA2a mRNAs and proteins and in the loss of the caffeine- and ryanodine-sensitive pool. The differentiated nonproliferative phenotype was maintained in low serum or in cells cultured at high density. In these conditions, RyR and SERCA2a were also present in RASMCs. Thus, expression of RyR and SERCA2a is repressed by cell proliferation, inducing loss of the corresponding Ca(2+) pool. In arterial smooth muscle, Ca(2+) release through RyRs is involved in vasodilation, and suppression of the ryanodine-sensitive pool might thus alter the control of vascular tone.

Identification of a polymorphic ryanodine receptor gene from Heliothis virescens (Lepidoptera: noctuidae)

cDNAs encoding the C-terminal 1172 amino acids of a ryanodine receptor (RyR) from the lepidopteran pest Heliothis virescens (Hv-RyR) have been cloned and characterised. Sequence comparisons, organisational studies on corresponding genomic regions and a genetic segregation analysis provide evidence for two polymorphic alleles of the Hv-RyR locus. Comparison of the Hv-RyR C-terminal amino acid sequence with equivalent regions of other RyRs reveals a high level of overall amino acid homology (74% identity with D. melanogaster and between 47.9 and 50.1% with vertebrate isoforms). Homologies are however not uniformly distributed, though regions of high and low similarity are consistent with patterns in other RyR isoforms. The structural similarity of Hv-RyR with other RyRs is also indicated by comparison of hydropathy profiles and other previously described functional domains. Such results are consistent with this region of Hv-RyR containing the Ca(2+) channel itself and being intimately involved in RyR regulation. Potential uses of the cDNAs described in the discovery and development of novel ryanodine like insecticides are discussed.

Calcium sparks in smooth muscle

Local intracellular Ca(2+) transients, termed Ca(2+) sparks, are caused by the coordinated opening of a cluster of ryanodine-sensitive Ca(2+) release channels in the sarcoplasmic reticulum of smooth muscle cells. Ca(2+) sparks are activated by Ca(2+) entry through dihydropyridine-sensitive voltage-dependent Ca(2+) channels, although the precise mechanisms of communication of Ca(2+) entry to Ca(2+) spark activation are not clear in smooth muscle. Ca(2+) sparks act as a positive-feedback element to increase smooth muscle contractility, directly by contributing to the global cytoplasmic Ca(2+) concentration ([Ca(2+)]) and indirectly by increasing Ca(2+) entry through membrane potential depolarization, caused by activation of Ca(2+) spark-activated Cl(-) channels. Ca(2+) sparks also have a profound negative-feedback effect on contractility by decreasing Ca(2+) entry through membrane potential hyperpolarization, caused by activation of large-conductance, Ca(2+)-sensitive K(+) channels. In this review, the roles of Ca(2+) sparks in positive- and negative-feedback regulation of smooth muscle function are explored. We also propose that frequency and amplitude modulation of Ca(2+) sparks by contractile and relaxant agents is an important mechanism to regulate smooth muscle function.

The effects of mutated skeletal ryanodine receptors on calreticulin and calsequestrin expression in the brain and pituitary gland of boars

Mutations in skeletal ryanodine receptors (sRyR) result in malignant hyperthermia in humans and Porcine Stress Syndrome (PSS) in pigs. Whether the sRyR is expressed in neuronal tissue and what impact it has on neuronal function is relatively unexplored. We have hypothesized that the presence of mutated sRyR may be accompanied by compensatory changes in Ca(2+)-binding protein expression. We were interested in whether pigs heterozygous for mutated sRyR would show changes in the expression of Ca(2+)-binding proteins, in specific regions of the brain, and whether changes in this expression would be accompanied by the presence of sRyR within that region. The objectives of the current experiments were to determine (1) whether calreticulin (CR) and calsequestrin (CS) are expressed in the pituitary gland and brain of the pig, (2) if boars heterozygous for mutated sRyR differed from wild-type boars in the expression of CR or CS, and (3) if altered Ca(2+)-binding protein expression would be accompanied by the presence of sRyR mRNA. Boars either heterozygous or wild-type (n=6) for the mutation in sRyR known to cause PSS, were euthanized and the pituitary gland and brains were collected for western blotting for CR and CS. An additional four wild-type boars were sacrificed and brains were collected for in situ hybridization for sRyR mRNA. Immunoreactive CR was expressed in porcine tissues with highest (p<0.0001) expression in the pituitary gland and lower but equivalent expression in the hypothalamus, frontal cortex, and hippocampus. Immunoreactive CS was not detectable in the pituitary gland while low levels were observed in the hypothalamus and frontal cortex. Dramatically higher (p<0.0001) levels of CS were found in the hippocampus. Genotype did not affect CR expression in the pituitary gland or any brain region examined. Immunoreactive CS levels were lower (p<0.002) in the hippocampus of heterozygous compared to wild-type boars. In situ hybridization experiments revealed the presence of sRyR mRNA in the hippocampus equally distributed across all cell subfields. In conclusion, both CR and CS were expressed in the porcine brain with specific patterns of expression across the brain regions examined. Boars heterozygous for mutated sRyR had lower CS in the hippocampus, which was accompanied by the expression of mRNA for sRyR.

Regional alterations in SR Ca(2+)-ATPase, phospholamban, and HSP-70 expression in chronic hibernating myocardium

We sought to identify mechanisms for chronic dysfunction in hibernating myocardium. Pigs were instrumented with a left anterior descending artery stenosis for 3 mo. Angiography demonstrated high-grade stenoses and hibernating myocardium with 1) severe anterior hypokinesis (P < 0.001 vs. shams), 2) reduced subendocardial perfusion [0.73 +/- 0.05 (SE) vs. 1.01 +/- 0.06 ml. min(-1). g(-1) in normal, P < 0.001], and 3) critically reduced adenosine flow (1.0 +/- 0.17 vs. 3.84 +/- 0.26 ml. min(-1). g(-1) in normal, P < 0.001). Histology did not reveal necrosis. Northern blot analysis of hibernating myocardium demonstrated regional downregulation in mRNAs for sarcoplasmic reticulum (SR) proteins phospholamban (0.76 +/- 0.08 vs. 1.07 +/- 0.06, P < 0.02) and SR Ca(2+)-ATPase (0.83 +/- 0.06 vs. 1.02 +/- 0.06, P < 0.05) with no change in calsequestrin (1.08 +/- 0.06 vs. 0.96 +/- 0.05, P = not significant). Heat shock protein (HSP)-70 mRNA was regionally induced in hibernating myocardium (2.4 +/- 0.3 vs. 1.0 +/- 0.11, P < 0.01). Directionally similar changes were confirmed by Western blot analysis of respective proteins. Our results indicate that hibernating myocardium exhibits a molecular phenotype that on a regional basis is similar to end-stage ischemic cardiomyopathy. This supports the hypothesis that SR dysfunction from reversible ischemia may be an early defect in the progression of left ventricular dysfunction.

Pregnant rat myometrial cells show heterogeneous ryanodine- and caffeine-sensitive calcium stores

Intracellular Ca(2+) release channels such as ryanodine receptors play crucial roles in the Ca(2+)-mediated signaling that triggers excitation-contraction coupling in muscles. Although the existence and the role of these channels are well characterized in skeletal and cardiac muscles, their existence in smooth muscles, and more particularly in the myometrium, is very controversial. We have now clearly demonstrated the expression of ryanodine receptor Ca(2+) release channels in rat myometrial smooth muscle, and for the first time, intracellular Ca(2+) concentration experiments with indo 1 on single myometrial cells have revealed the existence of a functional ryanodine- and caffeine-sensitive Ca(2+) release mechanism in 30% of rat myometrial cells. RT-PCR and RNase protection assay on whole myometrial smooth muscle demonstrate the existence of all three ryr mRNAs in the myometrium: ryr3 mRNA is the predominant subtype, with much lower levels of expression for ryr1 and ryr2 mRNAs, suggesting that the ryanodine Ca(2+) release mechanism in rat myometrium is largely encoded by ryr3. Moreover, using intracellular Ca(2+) concentration measurements and RNase protection assays, we have demonstrated that the expression, the percentage of cells responding to ryanodine, and the function of these channels are not modified during pregnancy.

Excitation-contraction coupling in gastrointestinal and other smooth muscles

The main contributors to increases in [Ca2+]i and tension are the entry of Ca2+ through voltage-dependent channels opened by depolarization or during action potential (AP) or slow-wave discharge, and Ca2+ release from store sites in the cell by the action of IP3 or by Ca(2+)-induced Ca(2+)-release (CICR). The entry of Ca2+ during an AP triggers CICR from up to 20 or more subplasmalemmal store sites (seen as hot spots, using fluorescent indicators); Ca2+ waves then spread from these hot spots, which results in a rise in [Ca2+]i throughout the cell. Spontaneous transient releases of store Ca2+, previously detected as spontaneous transient outward currents (STOCs), are seen as sparks when fluorescent indicators are used. Sparks occur at certain preferred locations--frequent discharge sites (FDSs)--and these and hot spots may represent aggregations of sarcoplasmic reticulum scattered throughout the cytoplasm. Activation of receptors for excitatory signal molecules generally depolarizes the cell while it increases the production of IP3 (causing calcium store release) and diacylglycerols (which activate protein kinases). Activation of receptors for inhibitory signal molecules increases the activity of protein kinases through increases in cAMP or cGMP and often hyperpolarizes the cell. Other receptors link to tyrosine kinases, which trigger signal cascades interacting with trimeric G-protein systems.

Ryanodine receptor gene expression thymomas

Ryanodine receptor (RyR) antibodies are present in sera of myasthenics with thymoma, and their titer correlates with morbidity and mortality. We investigated whether skeletal muscle RyR expression in thymic tissues could be the source of immune sensitization to the RyR. Skeletal muscle RyR gene expression was investigated using reverse transcription followed by semiquantitative polymerase chain reaction. Hyperplastic and normal thymuses expressed significant levels of RyR, but RyR gene transcripts was statistically less likely in thymomas than in hyperplastic and normal thymus (P < 0.05). The presence of RyR transcripts in thymomas did not correlate with myasthenic manifestations, thymic pathology, or serum RyR antibodies. We conclude that the skeletal muscle RyR in thymoma is not the inciting antigen for immune sensitization to RyR epitopes in thymoma-associated myasthenia gravis.

The structure, function, and cellular regulation of ryanodine-sensitive Ca2+ release channels

The fundamental biological process of Ca2+ signaling is known to be important in most eukaryotic cells, and inositol 1,2,5-trisphosphate and ryanodine receptors, intracellular Ca2+ release channels encoded by two distantly related gene families, are central to this phenomenon. Ryanodine receptors in the sarcoplasmic reticulum of skeletal and cardiac muscle have a predominant role in excitation-contraction coupling, but the channels are also present in the endoplasmic reticulum of noncontractile tissues including the central nervous system and the immune system. In all, three highly homologous ryanodine receptor isoforms have been identified, all very large proteins which assemble as (homo)tetramers of approximately 2 MDa. They contain large cytoplasmically disposed regulatory domains and are always associated with other structural or regulatory proteins, including calmodulin and immunophilins, which can have marked effects on channel function. The type 1 isoform in skeletal muscle is electromechanically coupled to surface membrane voltage sensors, whereas the remaining isoforms appear to be activated solely by endogenous cytoplasmic second messengers or other ligands, including Ca2+ itself ("Ca(2+)-induced Ca2+ release"). This review concentrates on ryanodine receptor structure-function relationships as probed by a variety of methods and on the molecular mechanisms of channel modulation at the cellular level (including evidence for the regulation of gene expression and transcription). It also touches on the relevance of ryanodine receptors to complex cellular functions and disease.

Partial cloning and differential expression of ryanodine receptor/calcium-release channel genes in human tissues including the hippocampus and cerebellum

Cellular Ca2+ signalling is an important factor in the control of neuronal metabolism and electrical activity. Although the roles of Ca2+-release channels are well established for skeletal and cardiac muscle, less is known about their expression and roles in the central nervous system, especially in the human brain. We have isolated partial complementary DNAs derived from the human ryanodine receptor Ca2+-release channel genes (ryr1, ryr2 and ryr3), and examined their expression in the human hippocampus and cerebellum. For comparison, we have included in our analysis an inositol trisphosphate Ca2+-release channel type I complementary RNA probe. All four messenger RNAs show widespread distribution in the human hippocampus, where ryr2 is the most abundant isoform, and all four are expressed in the human cerebellum. However, striking differences were seen between ryr and inositol trisphosphate Ca2+-release channel type I complementary RNA expression in the cerebellum, with inositol trisphosphate Ca2+-release channel type I messenger RNA being largely restricted to, and very highly expressed, in Purkinje cells, whereas ryr1, ryr2 and ryr3 were all expressed predominantly in the granular layer. The widespread expression of ryr isoforms in the human hippocampus and cerebellum suggests that ryanodine receptor proteins may have a central role in Ca2+ signalling and Ca2+ homeostasis in the human central nervous system. These may include roles in fundamental processes like synaptic plasticity. Furthermore, these Ca2+-release channels may be involved in pathogenic processes such as excitotoxicity, where excessive rises in intracellular Ca2+ concentration mediate neuronal cell death.

Purification and characterization of ryanodine receptor 3 from mammalian tissue

The ryanodine receptors are intracellular Ca2+ release channels that play a key role in cell signaling via Ca2+. There are three isoforms. Isoform 1 from skeletal muscle and isoform 2 from heart have been characterized. Isoform 3 is widely distributed in many mammalian tissues although in minuscule amounts. Its low abundance has hampered its study. We now describe methodology to isolate mammalian isoform 3 in amounts sufficient for biochemical and biophysical characterization. Bovine diaphragm sarcoplasmic reticulum fractions enriched in terminal cisternae containing both isoforms 1 (>95%) and 3 (<5% of the ryanodine binding) served as starting source. Isoform 3 was selectively immunoprecipitated from the 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonic acid (CHAPS)-solubilized fraction and eluted with peptide epitope. Isoform 3 thus prepared is highly purified as characterized by SDS-polyacryamide gel electrophoresis, Coomassie Blue staining, and by high affinity ryanodine binding. The purified isoform 3 was incorporated into planar lipid bilayers, and its channel properties were studied. Channel characteristics in common with the other two isoforms are slope conductance, higher selectivity to Ca2+ versus K+ (PCa/K approximately 6), and response to drugs and ligands. In its response to Ca2+ and ATP, it more closely resembles isoform 2. The first two-dimensional structure of isoform 3 was obtained by cryoelectron microscopy and image enhancement techniques.

cDNA cloning and sequencing of the human ryanodine receptor type 3 (RYR3) reveals a novel alternative splice site in the RYR3 gene

The human ryanodine receptor type 3 (RYR3) was cloned from a fetal brain cDNA library and its complete sequence was determined (EMBL accession number AJ001515). The sequenced cDNA spanned 15,564 bp and contained an open reading frame of 14,613 bp. The corresponding protein consisted of 4870 amino acids with a calculated molecular mass of 552 kDa. Amino acid sequence identities to the RYR3 proteins from rabbit, mink, and chicken were 96%, 95%, and 83% respectively. A previously unidentified alternative splice site was detected generating a transcript that lacked bases 11,569-11,650 and encoded a truncated protein.

Localization of ryanodine receptors in smooth muscle

The ryanodine receptor (RyR) in aortic and vas deferens smooth muscle was localized using immunofluorescence confocal microscopy and immunoelectron microscopy. Indirect immunofluorescent labeling of aortic smooth muscle with anti-RyR antibodies showed a patchy network-like staining pattern throughout the cell cytoplasm, excluding nuclei, in aortic smooth muscle and localized predominantly to the cell periphery in the vas deferens. This distribution is consistent with that of the sarcoplasmic reticulum (SR) network, as demonstrated by electron micrographs of osmium ferrocyanide-stained SR in the two smooth muscles. Immunoelectron microscopy of vas deferens smooth muscle showed anti-RyR antibodies localized to both the sparse central and predominant peripheral SR elements. We conclude that RyR-Ca2+-release channels are present in both the peripheral and central SR in aortic and vas deferens smooth muscle. This distribution is consistent with the possibility that both regions are release sites, as indicated by results of electron probe analysis, which show a decrease in the Ca2+ content of both peripheral and internal SR in stimulated smooth muscles. The complex distribution of inositol 1,4,5-trisphosphate and ryanodine receptors (present study) is compatible with their proposed roles as agonist-induced Ca2+-release channels and origins of Ca2+ sparks, Ca2+ oscillations, and Ca2+ waves.

Intracellular calcium signalling in striated muscle cells

Calcium signalling in cells is dependent on a communication between channels/ transporters in two membrane structures: the cell membrane and the membranes of endo- and sarcoplasmic reticula (ER/SR). In general, cytosolic Ca2+ can be raised by influx of calcium over the cell membrane through three types of channels: voltage-, receptor-, and store-operated channels (VOCs, ROCs and SOCs). This small Ca2+ influx is most often amplified by a Ca2+ release from the ER/SR through two types of channels: the IP3-receptor and the ryanodine receptor (RyR), which are huge proteins identified and cloned in recent years. We focus on the 'synaptic' connection between VOCs (L-type calcium channels) and RyRs of the SR in heart and skeletal muscle. Depolarization of the cell membrane (an action potential) opens the VOC and moves it in the membrane. One VOC triggers opening of a certain number of underlying RyRs that together release a quantum of calcium from the SR, a calcium spark. The communication between the VOC and RyRs is probably achieved primarily by a mechanical link in skeletal muscle (voltage-controlled calcium release), and by the small inward calcium flux through the VOC in the heart (calcium-induced calcium release, CICR). Conditions as different as heart failure, myasthenia gravis, malignant hyperthermia, and skeletal muscle fatigue, may be examples of deteriorated control or function of the RyR.

Characterization of type 3 ryanodine receptor (RyR3) of sarcoplasmic reticulum from rabbit skeletal muscles

We investigated type 3 isoform (RyR3) of ryanodine receptor in rabbit skeletal muscles using an antibody specific for RyR3. By Western blot analysis and by immunoprecipitation, a single polypeptide for RyR3 was detected in sarcoplasmic reticulum vesicles from rabbit diaphragm but not in those from back muscle. The molecular mass was slightly smaller than that of RyR1, the major isoform in skeletal muscles. Each of RyR1 and RyR3 formed a homotetramer in rabbit diaphragm. RyR3 had a single class of [3H]ryanodine binding sites of high affinity (KD = 1.6 nM). From the Bmax of the binding, the content of RyR3 was estimated to be only 0.6% of RyR1 in rabbit diaphragm. -3H-Ryanodine binding to RyR3 was biphasically dependent on Ca2+, as is true of RyR1, and was stimulated further by adenine nucleotide, caffeine, or high salt concentration. Procaine and ruthenium red inhibited the binding. RyR3 was more resistant to Mg2+ inhibition than RyR1. Interestingly, RyR3 showed about a 7-fold lower Ca2+ sensitivity for activation than RyR1. Comparison with the counterparts in bullfrog skeletal muscles indicates that the Ca2+ sensitivities of RyR3 homologs are similar to each other, whereas those of RyR1 homologs are species-specific.

Ortho-substituted polychlorinated biphenyls alter microsomal calcium transport by direct interaction with ryanodine receptors of mammalian brain

A stringent structure-activity relationship among polychlorinated biphenyls (PCBs) possessing two or more ortho-chlorine substituents is observed for activation of ryanodine receptors in mammalian brain, revealing an arylhydrocarbon receptor-independent mechanism through which non-coplanar PCBs disrupt neuronal Ca2+ signaling. Of the congeners assayed, non-coplanar PCB 95 exhibits the highest potency (EC50 = 12-24 microM) toward activating high affinity [3H]ryanodine-binding in rat hippocampus, cerebellum, and cerebral cortex. Coplanar PCB 66 and PCB 126 have no ryanodine receptor activity in all brain regions examined. PCB 95 enhances [3H]ryanodine-binding affinity and capacity by significantly altering modulation by Ca2+ and Mg2+, thereby stabilizing a high affinity conformation of the ryanodine receptor. Ca2+ transport measurements using cortical microsomes reveal that PCB 95 discriminates between inositol 1,4,5-trisphosphate- and ryanodine-sensitive stores. PCB 95 selectively mobilizes Ca2+ from ryanodine-sensitive stores in a dose-dependent manner (EC50 = 3.5 microM) and is completely inhibited by ryanodine receptor blockers, whereas coplanar PCBs are inactive. These data demonstrate that ortho-substituted PCBs disrupt Ca2+ transport in central neurons by direct interaction with ryanodine receptors, showing high selectivity and specificity. Alteration of Ca2+ signaling mediated by ryanodine receptors in specific regions of the central nervous system may account, at least in part, for the significant impact of these agents toward neurodevelopment and neuroplasticity in mammals.

Structural components of ryanodine responsible for modulation of sarcoplasmic reticulum calcium channel function

Comparative molecular field analysis (CoMFA) was used to analyze the relationship between the structure of a group of ryanoids and the modulation of the calcium channel function of the ryanodine receptor. The conductance properties of ryanodine receptors purified from sheep heart were measured using the planar, lipid bilayer technique. The magnitude of the ryanoid-induced fractional conductance was strongly correlated to specific structural loci on the ligand. Briefly, electrostatic effects were more prominent than steric effects. The 10-position of the ryanoid had the greatest influence on fractional conductance. Different regions of the ligand have opposing effects on fractional conductance. For example, steric bulk at the 10-position is correlated with decreased fractional conductance, whereas steric bulk at the 2-position (isopropyl position) is correlated with increased fractional conductance. In contrast to fractional conductance, the 3-position (the pyrrole locus) had the greatest influence on ligand binding, whereas the 10-position had comparatively little influence on binding. Two possible models of ryanodine action, a direct (or channel plug) mechanism and an allosteric mechanism, were examined in light of the CoMFA. Taken together, the data do not appear to be consistent with direct interaction between ryanodine and the translocating ion. The data appear to be more consistent with an allosteric mechanism. It is suggested the ryanoids act by inducing or stabilizing a conformational change in the ryanodine receptor that results in the observed alterations in cation conductance.

Differences in sarcoplasmic reticulum gene expression in myocardium from patients undergoing cardiac surgery. Quantification of steady-state levels of messenger RNA using the reverse transcription-polymerase chain reaction

Little is known about any alterations in sarcoplasmic reticulum (SR) gene expression associated with cardiac diseases of varying degrees of severity. We assessed, using the reverse transcription-polymerase chain reaction (RT-PCR) technique, SR Ca2+ transport protein gene expression in small tissue samples from failing hearts in patients undergoing cardiac surgery. Total RNA was extracted from 30- to 50-mg samples from the hearts of 13 patients with coronary artery disease, congenital heart disease, or valvular heart disease. We used RT-PCR to synthesize and amplify cDNA encoding cardiac SR Ca(2+)-ATPase, ryanodine receptor (RYR), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The amount of each mRNA in the sample was expressed relative to the amount of GAPDH mRNA. The expression level of each mRNA was correlated with the cardiac functional index. The mRNA levels for Ca(2+)-ATPase and RYR varied between heart samples, but showed a positive correlation with left ventricular ejection fraction. Ca(2+)-ATPase mRNA levels showed in inverse relationship with plasma brain natriuretic peptide. In addition, we isolated partial cDNA encoding a human cardiac RYR. The cDNA consisted of 487 nucleotides, and the nucleotide and deduced amino acid sequences showed 93% and 99% homology, respectively, to those of rabbit cardiac RYR. These results suggest that decreased levels of mRNA for SR Ca2+ transport protein could be related to abnormal cardiac function, regardless of the etiology of the heart disease. RT-PCR provides a rapid and economical way of quantifying the expression of multiple genes in small specimens and may, therefore, aid understanding of the pathophysiology and treatment of heart disease.

Ryanodine receptor expression in the kidney and a non-excitable kidney epithelial cell

An oligonucleotide probe to a conserved 3' region within the three identified ryanodine receptor-calcium release channel isoforms hybridized to a single clone from a rabbit kidney cDNA library. The kidney clone encoded the carboxyl-terminal 338 amino acids within the putative transmembrane domain of the type 2 ryanodine receptor sequence. Reverse transcriptase-polymerase chain reaction with isoform-specific oligonucleotide primers demonstrated the presence of the type 2 ryanodine receptor transcript in rabbit kidney, as well as in a non-excitable cell line, LLC-RK1, derived from rabbit kidney epithelial cells. Amplification by rapid amplification of 5' cDNA ends indicated the kidney type 2 ryanodine receptor transcript extended >7000 base pairs from the stop codon and is therefore not homologous to the short RyR-1 transcript of approximately 2500 base pairs previously observed in rabbit brain. [3H]Ryanodine binding and immunoblot analysis with a type 2 ryanodine receptor-specific antibody demonstrated that the native type 2 ryanodine receptor protein is expressed in the kidney. These observations suggest that the type 2 ryanodine receptor isoform may play a functional role in regulating intracellular calcium homeostasis in non-excitable cells.

No association between the neuroleptic malignant syndrome and mutations in the RYR1 gene associated malignant hyperthermia

The neuroleptic malignant syndrome (NMS) is a drug-induced disease caused by neuroleptics, but the pathogenesis of NMS is unknown. Since NMS is similar to malignant hyperthermia (MH) in clinical features and treatment, 6 mutations in the skeletal muscle ryanodine receptor (RYR1) gene, which were associated with MH, were investigated in unrelated NMS patients by single-strand conformation polymorphism analysis (SSCP). As a result, MH-susceptible RYR1 mutations were not detected in our NMS patients. A single base substitution, C7278T, was detected in one patient whose serum CPK level was repetitively elevated, but his other major symptoms did not fulfil the clinical criteria for NMS. Our results do not support the association between the neuroleptic malignant syndrome and mutations in the RYR1 gene associated with malignant hyperthermia.

Tissue-specific alternative splicing of mouse brain type ryanodine receptor/calcium release channel mRNA

We detected alternative splicing of the mouse brain type ryanodine receptor (RyR3) mRNA. The splicing variant was located in the transmembrane segment. The non-splicing type (RyR3-II) included a stretch of 341 bp, and that of the 13th codon was stop codon TAA. Reverse transcription-polymerase chain reaction (RT-PCR) analysis shows that RyR3-II mRNA was expressed in various peripheral tissues and brain at all developmental stages. However, interestingly, the splicing type (RyR3-I) mRNA was detected only in the cerebrum. These findings suggest that the splicing variants RyR3-I and RyR3-II may generate functional differences of RyR3 in a tissue-specific manner.

The porcine skeletal muscle ryanodine receptor gene structure coding region 1 to 10614 harbouring 71 exons

The skeletal muscle ryanodine receptor (RYR1) belongs to a family of calcium release channels that are expressed in different tissues. The RYR1 gene is one of the largest genes characterized, so far, containing a 15253 nucleotide ORF in swine. To study the genomic organization of the porcine skeletal muscle ryanodine receptor gene we have isolated seven genomic fragments spanning 72.7 kb of chromosomal DNA of chromosome 6q12. This region harbours exons 1 to 71 coding for 3538 amino acids (69.6%) of the ryanodine receptor 1.

Cloning and characterization of the 5'-upstream regulatory region of the Ca(2+)-release channel gene of cardiac sarcoplasmic reticulum

To elucidate the transcriptional regulation mechanism for the Ca(2+)-release channel gene of the cardiac sarcoplasmic reticulum (RYR2), we isolated and analyzed the 5'-upstream flanking region of the gene. Sequence analysis indicated that the core promoter region lacks canonical TATA and CAAT boxes, but contains three overlapping GC boxes. A gel shift assay indicated that Sp1 binds to the region containing the GC boxes. Different 5'-deletion constructs in the 5'-flanking region of the RYR2 gene were fused to the luciferase gene, and their promoter activity in rat neonatal cardiac myocytes was subsequently determined. The results revealed the presence of a region containing positive regulatory elements in the 5'-flanking region. Analyses of substitutional mutations introduced into the GC boxes and the regulatory region indicated that in addition to the GC box located at -56 to -51, two regulatory elements (RYR2P1 and RYR2P2) are essential for the promoter activity. These results indicated that Sp1 and transcription factors that bind to RYR2P1 and RYR2P2 cooperatively enhance the expression of the RYR2 gene. In a transient transfection experiment involving promoter-luciferase gene constructs in skeletal muscle cells, we identified a negative regulatory region between positions -209 and -90 that represses the expression of the RYR2 gene in skeletal muscle cells.

The pyrrole locus is the major orienting factor in ryanodine binding

Ryanodine, a natural product, is a complex modulator of a class of intracellular Ca2+ release channels commonly called the ryanodine receptors. Ryanodine analogs can cause the channel to persist in long-lived, subconductance states or, at high ligand concentrations, in closed, nonconducting states. In this paper, we further explore the relationship between structure and ryanodine binding to striated muscle. Ryanodine, 3-epiryanodine, and 10-ryanodine are three structural isomers of ryanodine. The dissociation constants of these compounds were measured using rabbit skeletal muscle ryanodine receptors. Placing the pyrrole carbonyl group at the 3-epi- and 10-positions of ryanodol largely restores the large loss of binding energy observed when ryanodine is hydrolyzed to ryanodol. Comparative molecular field analysis successfully predicts the enhanced binding and indicates that the pyrrole group controls the orientation of ligand binding. We propose that the ryanoids are reorientated in the binding site of the ryanodine receptors such that the pyrrole always occupies the same subsite. By applying this model, the binding constants of other ryanoids are predicted.

Calcium dependence of ryanodine-sensitive calcium channels from brain cortex endoplasmic reticulum

Endoplasmic reticulum vesicles isolated from rat brain cortex and fused with lipid bilayers displayed ryanodine-sensitive calcium channels, with three cytoplasmic calcium dependences. A: Channels (n=5) stimulated by Ca2+ (K0.5=1.2 microM and nHill=1.9) and not inhibited up to 0.5 mM Ca2+. B: Channels (n=14) cooperatively activated (K0.5=6.9 microM and nHill=1.8), and inhibited by Ca2+ (K0.5=152 microM and nHill=1.8). C: Low Po (<0.1) channels (n=22), non-cooperatively activated and inhibited with the same K0.5=26.3 microM Ca2+. These three types of responses to cytoplasmic [Ca2+] may underlie separate calcium release pathways in neurons of rat brain cortex.

Expression and function of ryanodine receptors in nonexcitable cells

We have used reverse transcriptase-polymerase chain reaction to investigate the expression of ryanodine receptors in several excitable and nonexcitable cell types. Consistent with previous reports, we detected ryanodine receptor expression in brain, heart, and skeletal muscle. In addition, we detected ryanodine receptor expression in various other excitable cells including PC 12 and A7r5 cells. Several muscle cell lines (BC3H1, C2C12, L6, and Sol8) weakly expressed ryanodine receptor when undifferentiated but strongly expressed type 1 and type 3 ryanodine receptor isoforms when differentiated into a muscle phenotype. Only 2 (HeLa and LLC-PK1 cells) out of 11 nonexcitable cell types examined expressed ryanodine receptors. Expression of ryanodine receptors at the protein level in these cells was confirmed using [3H]ryanodine binding. We also investigated the function of ryanodine receptors in Ca2+ signaling in HeLa cells using single-cell Fura-2 imaging. Neither caffeine nor ryanodine caused a detectable elevation of cytoplasmic Ca2+ in single HeLa cells. However, ryanodine caused a significant decrease in the amplitude of Ca 2+ signals evoked by repetitive stimulation with ATP. These studies show that ryanodine receptors are expressed in some nonexcitable cell types and furthermore suggest that the ryanodine receptors may be involved in a subtle regulation of intracellular Ca2+ responses.

Regulation of tissue-specific expression of the skeletal muscle ryanodine receptor gene

The ryanodine receptors (RYR) are a family of calcium release channels that are expressed in a variety of tissues. Three genes, i. e. ryr1, ryr2, and ryr3, have been identified coding for a skeletal muscle, cardiac muscle, and brain isoform, respectively. Although, the skeletal muscle isoform (RYR1) was shown to be expressed predominantly in skeletal muscle, expression was also detected in the esophagus and brain. To analyze the transcriptional regulation of the RYR1 gene, we have constructed chimeric genes composed of the upstream region of the RYR1 gene and the bacterial chloramphenicol acetyltransferase (CAT) gene and transiently transfected them into primary cultured porcine myoblasts, myotubes, and fibroblasts. A 443-base pair region upstream from the transcription start site was sufficient to direct CAT activity without tissue specificity. Deletion of a 61-base pair fragment from the 5'-end of the promoter resulted in a marked reduction of CAT activity in all three tissue types. A similar reduction of expression was observed when using a construct with the first intron in antisense orientation upstream from the promoter. In contrast, the first intron in sense orientation enhanced expression only in myotubes, while expression was repressed in fibroblasts and myoblasts. Gel retardation analyses showed DNA binding activity in nuclear extracts for two upstream DNA sequence elements. Our data suggest that (i) RYR1 gene expression is regulated by at least two novel transcription factors (designated RYREF-1 and RYREF-2), and (ii) tissue specificity results from a transcriptional repression in nonmuscle cells mediated by the first intron.

Dihydropyridine receptor-ryanodine receptor interactions in skeletal muscle excitation-contraction coupling

Much recent progress has been made in our understanding of the mechanism of sarcoplasmic reticulum Ca2+ release in skeletal muscle. Vertebrate skeletal muscle excitation-contraction (E-C) coupling is thought to occur by a "mechanical coupling" mechanism involving protein-protein interactions that lead to activation of the sarcoplasmic reticulum (SR) ryanodine receptor (RyR)/Ca2+ release channel by the voltage-sensing transverse (T-) tubule dihydropyridine receptor (DHPR)/Ca2+ channel. In a subsequent step, the released Ca2+ amplify SR Ca2+ release by activating release channels that are not linked to the DHPR. Experiments with mutant muscle cells have indicated that skeletal muscle specific DHPR and RyR isoforms are required for skeletal muscle E-C coupling. A direct functional and structural interaction between a DHPR-derived peptide and the RyR has been described. The interaction between the DHPR and RyR may be stabilized by other proteins such as triadin (a SR junctional protein) and modulated by phosphorylation of the DHPR.

Isolation and partial cloning of ryanodine-sensitive Ca2+ release channel protein isoforms from human myometrial smooth muscle

Partial cDNAs of the ryanodine receptor were cloned using PCR analysis from reverse transcribed total and mRNA, extracted from freshly isolated pregnant, non-pregnant, and cultured human myometrial smooth muscle. The identity of these clones was confirmed by nucleotide sequencing of the fragments and indicate the expression of both the skeletal and brain ryanodine receptor isoforms in these preparations. In freshly isolated non-pregnant myometrial tissue, membrane fractions displaying specific [3H]ryanodine binding activities were isolated using density gradient centrifugation. SDS-PAGE of the sucrose gradient fractions indicated the specific comigration of a polypeptide with a molecular mass of approximately 544 kDa with the ryanodine binding activity.

Embryonic chicken skeletal muscle cells fail to develop normal excitation-contraction coupling in the absence of the alpha ryanodine receptor. Implications for a two-ryanodine receptor system

Two ryanodine receptor (RyR), sarcoplasmic reticulum Ca2+ release channels, alpha and beta, co-exist in chicken skeletal muscles. To investigate a two-RyR Ca2+ release system, we compared electrically evoked Ca2+ transients in Crooked Neck Dwarf (cn/cn) cultured muscle cells, which do not make alpha RyR, and normal (+/?) cells. At day 3 in culture, Ca2+ release in +/? cells required extracellular Ca2+ (Ca2+o), and Ca2+ transients had slow kinetics. At day 5, Ca2+ release was Ca2+o-independent in 40% of the cells, and transients were more rapid. By day 7, all +/? cells had Ca2+o-independent Ca2+ release. Contractions were observed in +/? cells on all days. Ca2+ transients were observed in cn/cn cells on days 3, 5, and 7, but in each case they were Ca2+o-dependent and exhibited slow kinetics. Localized vesiculations, not contractions, occurred in cn/cn cells. By day 10, Ca2+ transients were no longer observed in cn/cn cells even in Ca2+o. Sarcoplasmic reticulum Ca2+ was not depleted, as caffeine induced Ca2+ transients. Thus, in the absence of alpha RyR there is a failure to develop Ca2+o-independent Ca2+ release and contractions and to sustain Ca2+o-dependent release. Moreover, contributions by the alpha RyR cannot be duplicated by the beta RyR alone.