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R Coronado

Publications and source records attributed to R Coronado.

At least 55 records · Page 3Linked to original sources
PubMed1991

Activation of the ryanodine receptor Ca2+ release channel of sarcoplasmic reticulum by a novel scorpion venom.

We identified a peptide fraction from the venom of the scorpion Buthotus hottentota that stimulated binding of [3H]ryanodine to ryanodine receptors of skeletal and cardiac sarcoplasmic reticulum and brain microsomes in a highly specific manner. Activity was concentrated in a peptide fraction of Mr 5,000-8,000. Assuming a single active peptide in this fraction, we estimated a dissociation constant of 20-30 nM for the interaction of the peptide with the ryanodine receptor. The whole venom and the purified fraction activated skeletal ryanodine receptor Ca2+ release channels incorporated into planar lipid bilayers. The venom produced a 10-fold increase in the mean open time and induced the appearance of a long lasting subconductance state not seen in controls. Changes were reversible and could be induced by the partially purified venom fraction. This novel scorpion venom should be helpful in establishing the role of ryanodine receptors in the initiation of intracellular Ca2+ release in striated muscle and in nonmuscle cells containing functional ryanodine receptors such as neurons and secretory cells.

Animals↗
PubMed1991

The brain ryanodine receptor: a caffeine-sensitive calcium release channel.

The release of stored Ca2+ from intracellular pools triggers a variety of important neuronal processes. Physiological and pharmacological evidence has indicated the presence of caffeine-sensitive intracellular pools that are distinct from the well-characterized inositol 1,4,5,-trisphosphate (IP3)-gated pools. Here we report that the brain ryanodine receptor functions as a caffeine- and ryanodine-sensitive Ca2+ release channel that is distinct from the brain IP3 receptor. The brain ryanodine receptor has been purified 6700-fold with no change in [3H]ryanodine binding affinity and shown to be a homotetramer composed of an approximately 500 kd protein subunit, which is identified by anti-peptide antibodies against the skeletal and cardiac muscle ryanodine receptors. Our results demonstrate that the brain ryanodine receptor functions as a caffeine-sensitive Ca2+ release channel and thus is the likely gating mechanism for intracellular caffeine-sensitive Ca2+ pools in neurons.

Animals↗
PubMed1991

Altered binding site for Ca2+ in the ryanodine receptor of human malignant hyperthermia.

The binding properties of [3H]ryanodine, a specific ligand of the receptor complex that forms the Ca2+ release channel of sarcoplasmic reticulum, were studied in normal (N) and malignant hyperthermia-susceptible (MH) human skeletal muscle. Integrity of the solubilized ryanodine receptor was demonstrated by single-channel recordings in planar bilayers and by the changes produced by activators and inhibitors of the Ca2+ release channel on the binding properties of [3H]ryanodine. N and MH receptors were capable of binding [3H]ryanodine in a Ca(2+)-dependent manner. Scatchard analysis showed that a single binding site for [3H]ryanodine was present in either N or MH muscle. Binding affinity was approximately the same in N and MH (Kd approximately 7 nM), when the Ca2+ concentration was greater than 30 microM. At 0.3 microM Ca2+, MH receptors displayed a higher affinity for [3H]ryanodine (Kd = 4.1 +/- 1.0 nM) than N receptors (Kd = 7.1 +/- 0.8 nM). The presence of a single Kd for [3H]ryanodine in MH muscle, distinct from that of N muscle, indicated that MH muscle does not have detectable levels of N receptors. Ca2+ dependence of [3H]ryanodine binding further suggested that MH receptors had a higher affinity for Ca2+ (Kd[Ca2+] = 120 +/- 50 nM) than N receptors (Kd[Ca2+] = 250 +/- 80 nM). Caffeine increased [3H]ryanodine binding at submicromolar [Ca2+], and the effect was larger in MH. Apparent affinity constants for caffeine were 13 +/- 1.8 mM in N and 6 +/- 0.8 mM in MH receptors. Evidently, the ryanodine receptor of MH-susceptible human skeletal muscle has an unusually high sensitivity to Ca2+ which is augmented by caffeine.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1990

Direct binding of verapamil to the ryanodine receptor channel of sarcoplasmic reticulum.

Radioligand binding experiments and single channel recordings demonstrate that verapamil interacts with the ryanodine receptor Ca2+ release channel of the sarcoplasmic reticulum of rabbit skeletal muscle. In isolated triads, verapamil decreased binding of [3H]Ryanodine with an IC50 of approximately 8 microM at an optimal pH 8.5 and pCa 4.3. Nitrendipine and d-cis-diltiazem did not interfere with binding of [3H]Ryanodine to triads, suggesting that the action of verapamil does not involve the dihydropyridine receptor. Single channel recordings showed that verapamil blocked Ca2+ release channels by decreasing open probability, duration of open events, and number of events per unit time. A direct interaction of verapamil with the ryanodine receptor peptide was demonstrated after purification of the approximately 400 kDa receptor protein from Chaps-solubilized triads. The purified receptor displayed high affinity for [3H]Ryanodine with a Kd of approximately 5 nM and a Bmax of approximately 400 pmol/mg. Verapamil and D600 decreased [3H]Ryanodine binding noncompetitively by reducing the Bmax. Thus the presence of binding sites for phenylalkylamines in the Ca2+ release channel was confirmed. Verapamil blockade of Ca2+ release channels may explain some of the paralyzing effects of phenylalkylamines observed during excitation-contraction coupling of skeletal muscle.

Animals↗
PubMed1990

Abnormal ryanodine receptor channels in malignant hyperthermia.

Previous studies have demonstrated a defect associated with the calcium release mechanism of sarcoplasmic reticulum (SR) from individuals susceptible to malignant hyperthermia (MH). To examine whether SR calcium release channels were indeed altered in MH, SR vesicles were purified from normal and MH susceptible (MHS) porcine muscle. The Ca2+ dependence of calcium efflux rates from 45Ca2(+)-filled SR vesicles was then compared with the Ca2+ dependence of single-channel recordings of SR vesicles incorporated into planar lipid bilayers. The rate constants of 45Ca2+ efflux from MHS SR were two to threefold larger than from normal SR over a wide range of myoplasmic Ca2+. Normal and MHS single channels were progressively activated in a similar fashion by cis Ca2+ from pCa 7 to 4. However, below pCa 4, normal channels were inactivated by cis Ca2+, whereas MHS channels remained open for significantly longer times. The altered Ca2+ dependence of channel inactivation in MHS SR was also evident when Ca2+ was increased on the trans side while cis Ca2+ was held constant. We propose that a defect in a low-affinity Ca2+ binding site is responsible for the altered gating of MHS SR channels. Such a defect could logically result from a mutation in the gene encoding the calcium release channel, providing a testable hypothesis for the molecular basis of this inherited disorder.

Animals↗
PubMed1990

Ca2+ release by inositol-trisphosphorothioate in isolated triads of rabbit skeletal muscle.

The effectiveness of the nonmetabolizable second messenger analogue DL-myo-inositol 1,4,5-trisphosphorothioate (IPS3) described by Cooke, A. M., R. Gigg, and B. V. L. Potter, (1987b. Jour. Chem. Soc. Chem. Commun. 1525-1526.) was examined in triads purified from rabbit skeletal muscle. A Ca2+ electrode uptake-release assay was used to determine the size and sensitivity of the IPS3-releasable pool of Ca2+ in isolated triads. Uptake was initiated by 1 mM MgATP, pCa 5.8, pH 7.5 Release was initiated when the free Ca2+ had lowered to pCa approximately 7. We found that 5-25 microM myo-inositol 1,4,5-trisphosphate (IP3), and separately IPS3, consistently released 5-20% of the Ca2+ pool actively loaded into triads. Single channel recording was used to determine if ryanodine receptor Ca2+ release channels were affected by IPS3 at the same myoplasmic Ca2+ and IPS3 concentrations. Open probability of ryanodine receptor Ca2+ release channels was monitored in triads fused to bilayers over long periods (200 s) in the absence and following addition of 30 microM IPS3 to the same channel. At myoplasmic pCa approximately 7, IPS3 had no effect in the absence of MgATP (Po = 0.0094 +/- 0.001 in control and Po = 0.01 +/- 0.006 after IPS3) and slightly increased activity in the presence of 1 mM MgATP (Po = 0.024 +/- 0.03 in control and Po = 0.05 +/- 0.03 after IPS3). Equally small effects were observed at higher myoplasmic Ca2+. The onset of channel activation by IPS3 or IP3 was slow, on the time scale 20-60 s. We suggest that in isolated triads of rabbit skeletal muscle, IP3-induced release of stored Ca2+ is probably not mediated by the opening of Ca2+ release channels.

Animals↗
PubMed1990

Internal and external effects of dihydropyridines in the calcium channel of skeletal muscle.

The agonist effect of the dihydropyridine (DHP) (-)Bay K 8644 and the inhibitory effects of nine antagonist DHPs were studied at a constant membrane potential of 0 mV in Ca channels of skeletal muscle transverse tubules incorporated into planar lipid bilayers. Four phenylalkylamines (verapamil, D600, D575, and D890) and d-cis-diltiazem were also tested. In Ca channels activated by 1 microM Bay K 8644, the antagonists nifedipine, nitrendipine, PN200-110, nimodipine, and pure enantiomer antagonists (+)nimodipine, (-)nimodipine, (+)Bay K 8644, inhibited activity in the concentration range of 10 nM to 10 microM. Effective doses (ED50) were 2 to 10 times higher when HDPs were added to the internal side than when added to the external side. This sidedness arises from different structure-activity relationships for DHPs on both sides of the Ca channel since the ranking potency of DHPs is PN200-110 greater than (-)nimodipine greater than nifedipine approximately S207-180 on the external side while PN200-110 greater than S207-180 greater than nifedipine approximately (-)nimodipine on the internal side. A comparison of ED50's for inhibition of single channels by DHPs added to the external side and ED50's for displacement of [3H]PN200-110 bound to the DHP receptor, revealed a good quantitative agreement. However, internal ED50's of channels were consistently higher than radioligand binding affinities by up to two orders of magnitude. Evidently, Ca channels of skeletal muscle are functionally coupled to two DHP receptor sites on opposite sides of the membrane.

Animals↗
PubMed1990

Open-channel subconductance state of K+ channel from cardiac sarcoplasmic reticulum.

We have characterized the K+ channel of canine cardiac sarcoplasmic reticulum in terms of its gating kinetics and conductance states. We demonstrate that the open channel dwells in two states, O1 and O2, where O1 is a true subconductance state of O2. The two open states are linked with a closed state by a cyclic gating scheme. Under certain circumstances, however, important information can be derived using a binary model. Each open state separately exhibited an ohmic current-voltage relation with unitary conductance values of 105 (O1) and 189 (O2) pS in 0.1 M K+. Gating between closed and open states was weakly voltage dependent, and we derive reaction rate constants for the state transitions. Finally, we postulate three models to explain the existence of a subconductance state (blockade, stenosis, flutter). We argue that a flutter model best accounts for our observations of O1.

Animals↗
PubMed1989

Inhibition of dihydropyridine-sensitive calcium channels by the plant alkaloid ryanodine.

At micromolar concentrations, ryanodine interacts with the dihydropyridine receptor of rabbit skeletal muscle transverse tubules. Ryanodine displaces specifically bound [3H]PN200-110 with an apparent inhibition constant of approx. 95 microM and inhibits dihydropyridine-sensitive calcium channels in the same preparation with an IC50 of approx. 45 microM. These concentrations of ryanodine are approximately three orders of magnitude higher than those required to saturate binding of the alkaloid to the ryanodine receptor of sarcoplasmic reticulum and to open the calcium release channel of sarcoplasmic reticulum (i.e. 20 nM (1988) J. Gen. Physiol. 92, 1-26). Thus at sufficiently high dose, ryanodine may affect SR as well as plasma membrane Ca permeabilities.

Alkaloids↗
PubMed1989

Reconstitution of ionic channels from human heart.

This report is the first description of single ion channels from human myocardium. Using explanted human left ventricular tissue, we have studied three K-conducting and two anion-conducting channels. We report our observations of gating and ionic selectivity properties of these channels which, we argue, derive from both sarcolemmal and sarcoplasmic reticulum membranes. We postulate that one channel is the K-conducting channel (SR K channel) from human cardiac sarcoplasmic reticulum. Another channel is similar to a dimeric Cl- channel from Torpedo electroplax, displaying two equally spaced levels of open state conductance.

Animals↗
PubMed1989

Potassium channel of cardiac sarcoplasmic reticulum is a multi-ion channel.

We have characterized mechanisms of ionic permeation in the K channel of canine cardiac sarcoplasmic reticulum (SR K channel). Ionic selectivity, as measured by relative permeabilities, followed Eisenman sequence l, a low field strength sequence. Slope conductance measured in symmetrical solutions across the bilayer followed Eisenman sequence V. In all cases, the selectivity characteristics of the prominent subconductance state (O1) were similar to those of the main-state (O2). Further, our studies have revealed that this channel differs in three significant ways from the highly characterized SR K channel of skeletal muscle. First, the ratio of permeabilities Cs+ to K+ was a complex function of ion concentration. Second, the concentration dependence of conductance was not well described by the Michaelis-Menten formalism. Instead, we modeled the observed relations using a more general approach based on classical rate theory. Third, mole fraction experiments (Cs+ with K+) demonstrated a prominent anomalous effect. Certain of our Cs+ data required the Eyring rate theory approach for adequate interpretation. We adopted a symmetrical energy profile incorporating ion-ion interaction and thereby accounted for much of the data. We conclude that the canine cardiac SR K channel is significantly different from that of skeletal muscle, and it may accommodate more than one ion at a time.

Animals↗
PubMed1989

Reconstitution of the ATP-sensitive potassium channel of skeletal muscle. Activation by a G protein-dependent process.

Potassium channels inhibited by adenosine-5'-trisphosphate, K(ATP), found in the transverse tubular membrane of rabbit skeletal muscle were studied using the planar bilayer recording technique. In addition to the single-channel properties of K(ATP) we report its regulation of Mg2+ and by the guanosine-5'-trisphosphate analogue, GTP-y(gamma)-S. The K(ATP) channel (a) has a conductance of 67 pS in 250 mM internal, 50 mM external KCl, and rectifies weakly at holding potentials more positive than 50 mV, (b) is not activated by internal Ca2+ or membrane depolarization, (c) has a permeability ratio PK/PNa greater than 50, and (d) is inhibited by millimolar internal ATP. Activity of K(ATP), measured as open channel probability as a function of time, was unstable at all holding potentials and decreases continuously within a few minutes after a recording is initiated. After a decrease in activity, GTP-y-S (100 microM) added to the internal side reactivated K(ATP) channels but only transiently. In the presence of internal 1 mM Mg2+, GTP-y-S produced a sustained reactivation lasting 20-45 min. Incubation of purified t-tubule vesicles with AlF4 increased the activity of K(ATP) channels, mimicking the effect of GTP-y-S. The effect of AlF4 and the requirement of GTP-y-S plus Mg2+ for sustained channel activation suggests that a nucleotide-binding G protein regulates ATP-sensitive K channels in the t-tuble membrane of rabbit skeletal muscle.

Adenosine Triphosphate↗
PubMed1989

The probe, a balloon-on-the-wire: clinical experience with a new low-profile, fixed-wire balloon catheter system.

We reviewed the clinical records of the 1st 144 consecutive patients in whom the Probe trade mark, a balloon-on-the-wire, was used for percutaneous transluminal coronary angioplasty at the Texas Heart Institute. The goal of our retrospective study was to establish the efficacy and safety of this new balloon catheter. The Probe was used in 227 lesions, most of which were considered severe and difficult to pass. The Probe was the 1st catheter used in 160 lesions (70%), and in 67 lesions (30%) the Probe was used after other balloon catheters. In 70.9% (161/227) of lesions treated, the Probe reduced the stenosis to less than 50% of the luminal diameter. Of 144 patients treated, 116 (81%) had a successful result: 98 of these had adequate recanalization of all vessels treated, while 17 had adequate recanalization of the most significant vessels. A relatively high number of lesions (17 lesions, 7.5%) became totally occluded during the procedure. Eight patients (6%) required emergency surgery because of impending infarction. No hospital deaths occurred, and there were only 2 patients who suffered transmural myocardial infarction. Of the 160 Probe devices used, 23 (14%) malfunctioned: the balloon ruptured in 11 procedures; the balloon twisted, causing "balloon volvulus," in 5; the balloon failed to deflate in 4; and the tip detached in 3. The Probe has significant advantages over other balloon systems for treating severe coronary lesions because of its low profile, but it is also less reliable and safe. Our results show that the Probe should be used with great care, and only in treating lesions not amenable to treatment with removable-guidewire catheters.

Journal Article↗
PubMed1989

Septal myotomy-myomectomy versus mitral valve replacement in hypertrophic cardiomyopathy. Ten-year follow-up in 185 patients.

Between 1963 and 1985, 185 patients with hypertrophic cardiomyopathy (HCM) were treated with septal myotomy-myomectomy (MM) or mitral valve replacement (MVR) at our institution; 127 of these underwent septal MM, and 58 underwent MVR alone. The 1-month mortality was 4.7% for the septal MM group and 6.9% for the MVR group (p = NS). The mean time of postoperative follow-up was 118 months, ranging between 1 and 196 months. The annual mortality was 0.7% for the septal MM group and 1.3% for the MVR group (p = NS). In the MVR group, 98% of patients had been assigned to New York Heart Association (NYHA) functional classes III and IV before surgery; only 24% were classified as such at 10-year follow-up (p less than 0.001). In the septal MM group, 90% were in NYHA functional classes III and IV before surgery whereas only 27% were in these two classes postoperatively (p less than 0.001). A comparison of preoperative and postoperative hemodynamic findings revealed a significant reduction in left ventricular outflow gradient at rest: from 69 +/- 41 mm Hg preoperatively to 10 +/- 22 mm Hg postoperatively (p less than 0.001) in the septal MM group and from 75 +/- 45 mm Hg preoperatively to 10 +/- 21 mm Hg postoperatively (p less than 0.001) in the MVR group. In addition, the MVR group had a significant postoperative reduction in mean left ventricular end-diastolic pressure, from 21 mm Hg preoperatively to 15 mm Hg postoperatively (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Reconstitution and phosphorylation of chloride channels from airway epithelium membranes.

Airway epithelial chloride secretion is controlled by the apical-membrane chloride permeability. Purified apical-membrane vesicles from bovine tracheal epithelium have now been shown to contain functional chloride channels by using the planar-bilayer technique. Three types of chloride channels were observed; a voltage-dependent, calcium-independent, 71-picoSiemen (in 150 mM NaCl) channel accounted for more than 80 percent of the vesicular chloride conductance and was under strict control of phosphorylation. The channel underwent a fast rundown in less than 2 to 3 minutes of recording, and reactivation required in situ exposure to a phosphorylating "cocktail" containing the catalytic subunit of the adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase. Mean open time and open probability were increased after phosphorylation, whereas slope conductance remained unchanged. Thus, metabolic control of tracheal chloride single channels can now be studied in vitro.

Animals↗
PubMed1988

Opening of dihydropyridine calcium channels in skeletal muscle membranes by inositol trisphosphate.

In many non-muscle cells, D-inositol 1,4,5-trisphosphate (InsP3) has been shown to release Ca2+ from intracellular stores, presumably from the endoplasmic reticulum. It is thought to be a ubiquitous second messenger that is produced in, and released from, the plasma membrane in response to extracellular receptor stimulation. By analogy, InsP3 in muscle cells has been postulated to open calcium channels in the sarcoplasmic reticulum (SR) membrane, which is the intracellular Ca2+ store that releases Ca2+ during muscle contraction. We report here that InsP3 may have a second site of action. We show that InsP3 opens dihydropyridine-sensitive Ca2+ channels in a vesicular preparation of rabbit skeletal muscle transverse tubules. InsP3-activated channels and channels activated by a dihydropyridine agonist in the same preparation have similar slope conductance and extrapolated reversal potential and are blocked by a dihydropyridine antagonist. This suggests that in skeletal muscle, InsP3 can modulate Ca2+ channels of transverse tubules from plasma membrane, in contrast to the previous suggestion that the functional locus of InsP3 is exclusively in the sarcoplasmic reticulum membrane.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗