No abstract available.
Muscle, Skeletal* ; Ryanodine Receptor Calcium Release Channel* ; Ryanodine* ; Sarcoplasmic Reticulum*

Heart Diseases ; Humans ; Ryanodine Receptor Calcium Release Channel

The secretion of insulin from pancreatic beta-cells is triggered by the influx of Ca2+ through voltage-dependent Ca2+ channels. The resulting elevation of intracellular calcium ([Ca2+]i) triggers additional Ca2+ release from internal stores. Less well understood are the mechanisms involved in Ca2+ mobilization from internal stores after activation of Ca2+ influx. The mobilization process is known as calcium-induced calcium release (CICR). In this study, our goal was to investigate the existence of and the role of caffeine-sensitive ryanodine receptors (RyRs) in a rat pancreatic beta-cell line, INS-1 cells. To measure cytosolic and stored Ca2+, respectively, cultured INS-1 cells were loaded with fura-2/AM or furaptra/AM. [Ca2+]i was repetitively increased by caffeine stimulation in normal Ca2+ buffer. However, peak [Ca2+]i was only observed after the first caffeine stimulation in Ca2+ free buffer and this increase was markedly blocked by ruthenium red, a RyR blocker. KCl-induced elevations in [Ca2+]i were reduced by pretreatment with ruthenium red, as well as by depletion of internal Ca2+ stores using cyclopiazonic acid (CPA) or caffeine. Caffeine-induced Ca2+ mobilization ceased after the internal stores were depleted by carbamylcholine (CCh) or CPA. In permeabilized INS-1 cells, Ca2+ release from internal stores was activated by caffeine, Ca2+, or ryanodine. Furthermore, ruthenium red completely blocked the CICR response in permeabilized cells. RyRs were widely distributed throughout the intracellular compartment of INS-1 cells. These results suggest that caffeine-sensitive RyRs exist and modulate the CICR response from internal stores in INS-1 pancreatic beta-cells.
Animals ; Caffeine ; Calcium ; Carbachol ; Cytosol ; Indoles ; Insulin ; Insulinoma ; Rats ; Ruthenium Red ; Ryanodine ; Ryanodine Receptor Calcium Release Channel

In the heart, Na+-Ca2+ exchange (NCX) is the major Ca2+ extrusion mechanism. NCX has been considered as a relaxation mechanism, as it reduces global [Ca2+]i raised during activation. However, if NCX locates in the close proximity to the ryanodine receptor, then NCX would curtail Ca2+ before its diffusion to global Ca2+i. This will result in a global [Ca2+]i decrease especially during its ascending phase rather than descending phase. Therefore, NCX would decrease the myocardial contractility rather than inducing relaxation in the heart. This possibility was examined in this study by comparing NCX-induced extrusion of Ca2+ after its release from SR in the presence and absence of global Ca2+i transient in the isolated single rat ventricular myocytes by using patch-clamp technique in a whole-cell configuration. Global Ca2+i transient was controlled by an internal dialysis with different concentrations of BAPTA added in the pipette. During stimulation with a ramp pulse from +100 mV to -100 mV for 200 ms, global Ca2+i transient was suppressed only mildly, and completely at 1 mmol/L, and 10 mmol/L BAPTA, respectively. In these situations, ryanodine-sensitive inward NCX current was compared using 100micromol/L ryanodine, Na+ depletion, 5 mmol/L NiCl2 and 1micromol/L nifedipine. Surprisingly, the result showed that the ryanodine-sensitive inward NCX current was well preserved after 10 mmol/L BAPTA to 91 % of that obtained after 1 mmol/L BAPTA. From this result, it is concluded that most of the NCX-induced Ca2+ extrusion occurs before the Ca2+ diffuses to global Ca2+i in the rat ventricular myocyte.
Animals ; Architectural Accessibility ; Dialysis ; Diffusion* ; Heart ; Muscle Cells* ; Nifedipine ; Patch-Clamp Techniques ; Rats* ; Relaxation ; Ryanodine ; Ryanodine Receptor Calcium Release Channel

Nitric Oxide (NO) is an important signaling molecule in the nociceptive process. Our previous study suggested that high concentrations of sodium nitroprusside (SNP), a NO donor, induce a membrane hyperpolarization and outward current through large conductances calcium-activated potassium (BKca) channels in substantia gelatinosa (SG) neurons. In this study, patch clamp recording in spinal slices was used to investigate the sources of Ca2+ that induces Ca2+-activated potassium currents. Application of SNP induced a membrane hyperpolarization, which was significantly inhibited by hemoglobin and 2-(4-carboxyphenyl) -4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide potassium salt (c-PTIO), NO scavengers. SNP-induced hyperpolarization was decreased in the presence of charybdotoxin, a selective BKCa channel blocker. In addition, SNP-induced response was significantly blocked by pretreatment of thapsigargin which can remove Ca2+ in endoplasmic reticulum, and decreased by pretreatment of dentrolene, a ryanodine receptors (RyR) blocker. These data suggested that NO induces a membrane hyperpolarization through BKca channels, which are activated by intracellular Ca2+ increase via activation of RyR of Ca2+ stores.
Animals ; Calcium* ; Charybdotoxin ; Endoplasmic Reticulum ; Humans ; Membranes ; Neurons* ; Nitric Oxide ; Nitroprusside ; Potassium ; Rats* ; Ryanodine Receptor Calcium Release Channel ; Ryanodine* ; Substantia Gelatinosa* ; Thapsigargin ; Tissue Donors

BACKGROUND AND PURPOSE: At least 100 Ryanodine receptor type 1 (RYR1) mutations associated with malignant hyperthermia (MH) and central core disease (CCD) have been identified, but 2 RYR1 mutations accompanying multiminicore myopathy in an MH and/or CCD family have been reported only rarely. METHODS: Fifty-three members of a large MH family were investigated with clinical, histopathologic, RYR1 mutation, and haplotyping studies. Blood creatine kinase (CK) and myoglobin levels were also measured where possible. RESULTS: Sequencing of the entire RYR1 coding region identified a double RYR1 mutation (R2435H and A4295V) in MH/CCD regions 2 and 3. Haplotyping analysis revealed that the two missense heterozygous mutations (c.7304G>A and c.12891C>T) were always present on a common haplotype allele, and were closely cosegregated with histological multiminicores and elevated serum CK. All the subjects with the double mutation showed elevated serum CK and myoglobin, and the obtained muscle biopsy samples showed multiminicore lesions, but only two family members presented a late-onset, slowly progressive myopathy. CONCLUSIONS: We found multiminicore myopathy with clinical and histological variability in a large MH family with an unusual double RYR1 mutation, including a typical CCD-causing known mutant. These results suggest that multiminicore lesions are associated with the presence of more than two mutations in the RYR1 gene.
Alleles ; Biopsy ; Clinical Coding ; Creatine Kinase ; Haplotypes ; Humans ; Malignant Hyperthermia ; Muscles ; Muscular Diseases ; Myoglobin ; Myopathies, Structural, Congenital ; Myopathy, Central Core ; Ophthalmoplegia ; Ryanodine ; Ryanodine Receptor Calcium Release Channel

AIMThe characteristics of ryanodine receptor in rat cardiac sarcoplasmic reticulum (SR) and nuclear envelope (NE) were studied.

METHODSVelocity and isopyknic gradient centrifugation was employed to fractionate rat SR and NE. Ryanodine receptor was assayed with [3H] ryanodine saturate binding to the preparations.

RESULTSThe maximal binding (Bmax) and dissociating constant (Kd) of ryanodine receptor in rat cardiac NE were, 1.7% and 60% of those in SR respectively. Phosphorylation in vitro by PKA and PKC increased Bmax of the receptors in SR by 372% and 121%, and augmented those in NE by 221% and 306%, without any effects on Kd.

CONCLUSIONRyanodine receptors were present in rat myocardial NE, with lower density and higher affinity than those located in SR, which can be activated by PKA and PKC.

Animals ; Calcium ; metabolism ; Kinetics ; Myocardium ; metabolism ; Nuclear Envelope ; metabolism ; physiology ; Phosphorylation ; Rats ; Rats, Sprague-Dawley ; Ryanodine ; metabolism ; Ryanodine Receptor Calcium Release Channel ; metabolism ; Sarcoplasmic Reticulum ; metabolism ; physiology

OBJECTIVETo examine the effects of procaine and lidocaine on intracellular Ca(2+) release from sarcoplasmic reticulum ryanodine-sensitive Ca(2+) stores.

METHODSThe experiment was performed on hippocampal slices from 60-80 g male Mongolian gerbils. Levels of intracellular Ca(2+) concentration in the slices were measured by microfluorometry. The slices were perfused with 50 mmol/L KCl containing medium for 30 seconds. Then, the medium was switched to physiological medium. After 5 min of incubation, the slice was perfused with 20 mmol/L caffeine containing physiology medium for 2 min. Following incubation, the slice was superfused with physiological medium until the end of the experiment. The effects of procaine and lidocanin (100 micro mol/L) on caffeine-evoked Ca(2+) release were evaluated by adding them to the medium after high K(+) medium perfusion.

RESULTSCaffeine induced a marked increase in intracellular Ca(2+) concentration which was then decreased 12% upon the addition of procaine (P < 0.05); however, lidocaine, did not induce a similar inhibitory reaction.

CONCLUSIONProcaine inhibits ryanodine-receptor mediated Ca(2+) release from intracellular Ca(2+) stores, while lidocaine may inhibit Ca(2+) release through other mechanisms.

Anesthetics, Local ; pharmacology ; Animals ; Calcium ; metabolism ; Gerbillinae ; Hippocampus ; drug effects ; metabolism ; Lidocaine ; pharmacology ; Male ; Procaine ; pharmacology ; Ryanodine ; pharmacology ; Ryanodine Receptor Calcium Release Channel ; physiology

Vascular smooth muscle cells can obtain a proliferative function in environments such as atherosclerosis in vivo or primary culture in vitro. Proliferation of vascular smooth muscle cells is accompanied by changes in ryanodine receptors (RyRs). In several studies, the cytosolic Ca2+ response to caffeine is decreased during smooth muscle cell culture. Although caffeine is commonly used to investigate RyR function because it is difficult to measure Ca2+ release from the sarcoplasmic reticulum (SR) directly, caffeine has additional off-target effects, including blocking inositol trisphosphate receptors and store-operated Ca2+ entry. Using freshly dissociated rat aortic smooth muscle cells (RASMCs) and cultured RASMCs, we sought to provide direct evidence for the operation of RyRs through the Ca2+- induced Ca2+-release pathway by directly measuring Ca2+ release from SR in permeabilized cells. An additional goal was to elucidate alterations of RyRs that occurred during culture. Perfusion of permeabilized, freshly dissociated RASMCs with Ca2+ stimulated Ca2+ release from the SR. Caffeine and ryanodine also induced Ca2+ release from the SR in dissociated RASMCs. In contrast, ryanodine, caffeine and Ca2+ failed to trigger Ca2+ release in cultured RASMCs. These results are consistent with results obtained by immunocytochemistry, which showed that RyRs were expressed in dissociated RASMCs, but not in cultured RASMCs. This study is the first to demonstrate Ca2+ release from the SR by cytosolic Ca2+ elevation in vascular smooth muscle cells, and also supports previous studies on the alterations of RyRs in vascular smooth muscle cells associated with culture.
Animals ; Atherosclerosis ; Caffeine ; Cell Culture Techniques ; Cytosol ; Immunohistochemistry ; Inositol ; Muscle, Smooth ; Muscle, Smooth, Vascular ; Myocytes, Smooth Muscle ; Perfusion ; Rats ; Ryanodine ; Ryanodine Receptor Calcium Release Channel ; Sarcoplasmic Reticulum

To investigate the properties of ryanodine binding sites of the bird skeletal SR vesicles, SDS PAGE, purification of RyR, and (3H)ryanodine binding study were carried out in the SR vesicles prepared from the chicken pectoral muscle. The chicken SR vesicles have two high molecular weight (HMW) protein bands as in eel SR vesicles on SDS PAGE. The HMW bands on SDS PAGE were found in the (3H) ryanodine peak fraction (Fr3-5) obtained from the purification step of the ryanodine receptor protein. Bmax and KD of the chicken (3H)ryanodine binding sites were 12.52 pmol/mg protein and 14.53 nM, respectively. Specific (3H)ryanodine binding was almost maximal at 50~100 micrometer Ca2+, but was not increased by 5 mM AMP and not inhibited by high Ca2+. Binding was significantly inhibited by 20~100 micrometer ruthenium red and 1 mM tetracaine, but slightly inhibited by Mg2+. From the above results, it is suggested that chicken SR vesicles have the ryanodine binding sites to which the binding of ryanodine is almost maximal at 50~10 micrometer Ca2+, is significantly inhibited by ruthenium red and tetracaine, slightly inhibited by Mg2+, but not affected by AMP and not inhibited by high Ca2+.
Binding Sites* ; Birds ; Chickens* ; Eels ; Electrophoresis, Polyacrylamide Gel ; Molecular Weight ; Ruthenium Red ; Ryanodine ; Ryanodine Receptor Calcium Release Channel ; Sarcoplasmic Reticulum ; Tetracaine