RESUMO
La participación del canal de Ca2+/receptor de rianodina en el acoplamiento excitación-contracción cardiaco se conoce desde finales de los años ochenta, cuando en varios trabajos trascendentales se comunicó por primera vez su purificación y se encontró que correspondía a las estructuras conocidas como «pies¼ localizadas en las cisternas terminales del retículo sarcoplásmico. Adicionalmente a su papel como canal responsable del aumento global y transitorio de Ca2+ que activa a la maquinaria contráctil durante el ciclo cardiaco, el receptor de rianodina también libera Ca2+ durante la fase de relajación, dando lugar a la fuga de Ca2+ en la diástole que en condiciones fisiológicas regula el nivel de Ca2+ luminal, pero cuando se encuentra alterada participa en la generación de arritmias adquiridas o hereditarias. Recientemente, el esfuerzo de diversos grupos de investigación se ha enfocado en el desarrollo de herramientas farmacológicas para controlar la fuga diastólica de Ca2+ que se presenta alterada en algunas enfermedades cardiacas. En esta revisión nos enfocamos en describir la participación del receptor de rianodina cardiaco en la fuga diastólica de Ca2+ así como los diversos enfoques terapéuticos que se han implementado para controlar su actividad exacerbada en la diástole.
The participation of the ionic Ca2+ release channel/ryanodine receptor in cardiac excitation-contraction coupling is well known since the late '80s, when various seminal papers communicated its purification for the first time and its identity with the "foot" structures located at the terminal cisternae of the sarcoplasmic reticulum. In addition to its main role as the Ca2+ channel responsible for the transient Ca2+ increase that activates the contractile machinery of the cardiomyocytes, the ryanodine receptor releases Ca2+ during the relaxation phase of the cardiac cycle, giving rise to a diastolic Ca2+ leak. In normal physiological conditions, diastolic Ca2+ leak regulates the proper level of luminal Ca2+, but in pathological conditions it participates in the generation of both, acquired and hereditary arrhythmias. Very recently, several groups have focused their efforts into the development of pharmacological tools to control the altered diastolic Ca2+ leak via ryanodine receptors. In this review, we focus our interest on describing the participation of cardiac ryanodine receptor in the diastolic Ca2+ leak under physiological or pathological conditions and also on the therapeutic approaches to control its undesired exacerbated activity during diastole.
Assuntos
Humanos , Arritmias Cardíacas/etiologia , Cálcio/fisiologia , Canal de Liberação de Cálcio do Receptor de Rianodina/fisiologia , DiástoleRESUMO
The participation of the ionic Ca(2+) release channel/ryanodine receptor in cardiac excitation-contraction coupling is well known since the late '80s, when various seminal papers communicated its purification for the first time and its identity with the "foot" structures located at the terminal cisternae of the sarcoplasmic reticulum. In addition to its main role as the Ca(2+) channel responsible for the transient Ca(2+) increase that activates the contractile machinery of the cardiomyocytes, the ryanodine receptor releases Ca(2+) during the relaxation phase of the cardiac cycle, giving rise to a diastolic Ca(2+) leak. In normal physiological conditions, diastolic Ca(2+) leak regulates the proper level of luminal Ca(2+), but in pathological conditions it participates in the generation of both, acquired and hereditary arrhythmias. Very recently, several groups have focused their efforts into the development of pharmacological tools to control the altered diastolic Ca(2+) leak via ryanodine receptors. In this review, we focus our interest on describing the participation of cardiac ryanodine receptor in the diastolic Ca(2+) leak under physiological or pathological conditions and also on the therapeutic approaches to control its undesired exacerbated activity during diastole.
Assuntos
Arritmias Cardíacas/etiologia , Cálcio/fisiologia , Canal de Liberação de Cálcio do Receptor de Rianodina/fisiologia , Diástole , HumanosRESUMO
Scorpion venoms are rich in ion channel-modifying peptides, which have proven to be invaluable probes of ion channel structure-function relationship. We previously isolated imperatoxin A (IpTxa), a 3.7 kDa peptide activator of Ca(2+)-release channels/ryanodine receptors (RyRs) [1,2,3] and founding member of the calcin family of scorpion peptides. IpTxa folds into a compact, mostly hydrophobic molecule with a cluster of positively-charged, basic residues polarized on one side of the molecule that possibly interacts with the phospholipids of cell membranes. To investigate whether IpTxa permeates external cellular membranes and targets RyRs in vivo, we perfused IpTxa on intact cardiomyocytes while recording field-stimulated intracellular Ca(2+) transients. To further investigate the cell-penetrating capabilities of the toxin, we prepared thiolated, fluorescent derivatives of IpTxa. Biological activity and spectroscopic properties indicate that these derivatives retain high affinity for RyRs and are only 5- to 10-fold less active than native IpTxa. Our results demonstrate that IpTxa is capable of crossing cell membranes to alter the release of Ca(2+)in vivo, and has the capacity to carry a large, membrane-impermeable cargo across the plasma membrane, a finding with exciting implications for novel drug delivery.
RESUMO
BACKGROUND AND PURPOSE: Members of the calcin family, presently including imperatoxin A, maurocalcin, opicalcins and hemicalcin, are basic, 33-mer peptide activators of ryanodine receptors (RyRs), the calcium channels of the sarcoplasmic reticulum (SR) that provide the majority of calcium for muscle contraction. Here we describe hadrucalcin, a novel member of this family. EXPERIMENTAL APPROACH: Hadrucalcin was isolated from the venom of Hadrurus gertschi. Amino acid sequence and mass were determined by Edman degradation and mass spectrometry respectively. A cDNA library was constructed to generate clones for DNA sequence determination. Biological activity of native toxin was confirmed with [(3)H]ryanodine binding, by using SR vesicles from cardiac and skeletal muscle, and with single skeletal (RyR1) and cardiac (RyR2) channels reconstituted in lipid bilayers. Hadrucalcin was applied to intact ventricular myocytes to investigate effects on calcium transients. The secondary structure of hadrucalcin was computer-modelled by using atomic coordinates from maurocalcin, a structurally similar peptide. KEY RESULTS: Hadrucalcin is distinguished from previously described congeners by two additional amino acids in its primary sequence and the lack of prominent amphipathicity. Hadrucalcin activated RyRs with high affinity (EC(50)= 37 nmol.L(-1)), induced a long-lasting subconductance state on RyR1 and RyR2, and rapidly (lag time approximately 2 s) penetrated ventricular cardiomyocytes, eliciting discharge of internal calcium stores and spontaneous contractions. CONCLUSIONS AND IMPLICATIONS: Hadrucalcin is a cell-permeant, powerful activator of RyRs, which has translational potential for targeted delivery of drugs to RyR as novel therapeutic intervention in arrhythmogenic disease.
Assuntos
Agonistas dos Canais de Cálcio/farmacologia , Peptídeos/farmacologia , Canal de Liberação de Cálcio do Receptor de Rianodina/fisiologia , Venenos de Escorpião/farmacologia , Escorpiões/química , Sequência de Aminoácidos , Animais , Sequência de Bases , Cálcio/metabolismo , Agonistas dos Canais de Cálcio/química , Permeabilidade da Membrana Celular , Cães , Feminino , Masculino , Camundongos , Modelos Moleculares , Dados de Sequência Molecular , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/fisiologia , Peptídeos/química , Estrutura Secundária de Proteína , Coelhos , Ensaio Radioligante , Venenos de Escorpião/química , Alinhamento de SequênciaRESUMO
Activation of Ca2+ release channels/ryanodine receptors (RyR) by the inward Ca2+ current (I(Ca)) gives rise to Ca(2+)-induced Ca2+ release (CICR), the amplifying Ca2+ signaling mechanism that triggers contraction of the heart. CICR, in theory, is a high-gain, self-regenerating process, but an unidentified mechanism stabilizes it in vivo. Sorcin, a 21.6 kDa Ca(2+)-binding protein, binds to cardiac RyRs with high affinity and completely inhibits channel activity. Sorcin significantly inhibits both the spontaneous activity of RyRs in quiescent cells (visualized as Ca2+ sparks) and the I(Ca)-triggered activity of RyRs that gives rise to [Ca2+]i transients. Since sorcin decreases the amplitude of the [Ca2+]i transient without affecting the amplitude of I(Ca), the overall effect of sorcin is to reduce the "gain" of excitation-contraction coupling. Immunocytochemical staining shows that sorcin localizes to the dyadic space of ventricular cardiac myocytes. Ca2+ induces conformational changes and promotes translocation of sorcin between soluble and membranous compartments, but the [Ca2+] required for the latter process (ED50 = approximately 200 microM) appears to be reached only within the dyadic space. Thus, sorcin is a potent inhibitor of both spontaneous and I(Ca)-triggered RyR activity and may play a role in helping terminate the positive feedback loop of CICR.
Assuntos
Proteínas de Ligação ao Cálcio/fisiologia , Contração Miocárdica/fisiologia , Miócitos Cardíacos/metabolismo , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Retículo Sarcoplasmático/metabolismo , Animais , Cálcio/metabolismo , Sinalização do Cálcio/fisiologia , Imuno-HistoquímicaRESUMO
Activation of Ca2+ release channels/ryanodine receptors (RyR) by the inward Ca2+ current (ICa) gives rise to Ca2+-induced Ca2+ release (CICR), the amplifying Ca2+ signaling mechanism that triggers contraction of the heart. CICR, in theory, is a high-gain, self-regenerating process, but an unidentified mechanism stabilizes it in vivo. Sorcin, a 21.6 kDa Ca2+-binding protein, binds to cardiac RyRs with high affinity and completely inhibits channel activity. Sorcin significantly inhibits both the spontaneous activity of RyRs in quiescent cells (visualized as Ca2+ sparks) and the ICa-triggered activity of RyRs that gives rise to [Ca2+]i transients. Since sorcin decreases the amplitude of the [Ca2+]i transient without affecting the amplitude of ICa, the overall effect of sorcin is to reduce the "gain" of excitation-contraction coupling. Immunocytochemical staining shows that sorcin localizes to the dyadic space of ventricular cardiac myocytes. Ca2+ induces conformational changes and promotes translocation of sorcin between soluble and membranous compartments, but the [Ca2+] required for the latter process (ED50 = ~200 mM) appears to be reached only within the dyadic space. Thus, sorcin is a potent inhibitor of both spontaneous and ICa-triggered RyR activity and may play a role in helping terminate the positive feedback loop of CICR.