1
|
Place AR, Ramos-Franco J, Waters AL, Hamann MT. A Toxic Sterolysin From a 1950s Culture of Gymnodinium Veneficum Ballantine. Res Sq 2024:rs.3.rs-3970188. [PMID: 38585775 PMCID: PMC10996815 DOI: 10.21203/rs.3.rs-3970188/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/09/2024]
Abstract
In 1957 Abbott and Ballentine described a highly toxic activity from a dinoflagellate isolated from the English Channel. in 1949 by Mary Park. From a culture maintained at Plymouth Laboratory since 1950, we have been able to isolate two toxic molecules (Abbotoxin and 59-E-Chloro-Abbotoxin), determine the planar structures by analysis of HRMS and 1D and 2D NMR spectra and found them to be karlotoxin (KmTx) congeners. Both toxins kill larval zebrafish with symptoms identical to that described by Abbot and Ballantine for gobies (Gobius virescens). Using surface plasma resonance the sterol binding specificity of karlotoxins is shown to require desmethyl sterols. Our results with black lipid membranes indicate that karlotoxin forms large-conductance channels in the lipid membrane, which are characterized by large ionic conductance, poor ionic selectivity, and a complex gating behavior that exhibits strong voltage dependence and multiple gating patterns. In addition, we show that KmTx 2 pore formation is a highly targeted mechanism involving sterol-specificity. This is the first report of the functional properties of the membrane pores formed by karlotoxins and are consistent with the intial observations of Abbott and Ballentine from 1957.
Collapse
Affiliation(s)
- Allen R Place
- University of Maryland Center for Environmental Sciences
| | | | | | | |
Collapse
|
2
|
Tambeaux A, Aguilar-Sánchez Y, Santiago DJ, Mascitti M, DiNovo KM, Mejía-Alvarez R, Fill M, Wayne Chen SR, Ramos-Franco J. Ligand sensitivity of type-1 inositol 1,4,5-trisphosphate receptor is enhanced by the D2594K mutation. Pflugers Arch 2023; 475:569-581. [PMID: 36881190 PMCID: PMC10105685 DOI: 10.1007/s00424-023-02796-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Revised: 02/06/2023] [Accepted: 02/12/2023] [Indexed: 03/08/2023]
Abstract
Inositol 1,4,5-trisphosphate receptor (IP3R) and ryanodine receptor (RyR) are homologous cation channels that mediate release of Ca2+ from the endoplasmic/sarcoplasmic reticulum (ER/SR) and thereby are involved in many physiological processes. In previous studies, we determined that when the D2594 residue, located at or near the gate of the IP3R type 1, was replaced by lysine (D2594K), a gain of function was obtained. This mutant phenotype was characterized by increased IP3 sensitivity. We hypothesized the IP3R1-D2594 determines the ligand sensitivity of the channel by electrostatically affecting the stability of the closed and open states. To test this possibility, the relationship between the D2594 site and IP3R1 regulation by IP3, cytosolic, and luminal Ca2+ was determined at the cellular, subcellular, and single-channel levels using fluorescence Ca2+ imaging and single-channel reconstitution. We found that in cells, D2594K mutation enhances the IP3 ligand sensitivity. Single-channel IP3R1 studies revealed that the conductance of IP3R1-WT and -D2594K channels is similar. However, IP3R1-D2594K channels exhibit higher IP3 sensitivity, with substantially greater efficacy. In addition, like its wild type (WT) counterpart, IP3R1-D2594K showed a bell-shape cytosolic Ca2+-dependency, but D2594K had greater activity at each tested cytosolic free Ca2+ concentration. The IP3R1-D2594K also had altered luminal Ca2+ sensitivity. Unlike IP3R1-WT, D2594K channel activity did not decrease at low luminal Ca2+ levels. Taken together, our functional studies indicate that the substitution of a negatively charged residue by a positive one at the channels' pore cytosolic exit affects the channel's gating behavior thereby explaining the enhanced ligand-channel's sensitivity.
Collapse
Affiliation(s)
- Allison Tambeaux
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA
| | - Yuriana Aguilar-Sánchez
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA.,Molecular Physiology & Biophysics, Baylor College of Medicine, Houston, TX, USA
| | - Demetrio J Santiago
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA.,Centro Nacional de Investigaciones Cardiovasculares, Madrid, Spain
| | | | - Karyn M DiNovo
- Department of Physiology, Midwestern University, Downers Grove, IL, USA
| | | | - Michael Fill
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA
| | - S R Wayne Chen
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA.,Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, AB, Canada
| | - Josefina Ramos-Franco
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA.
| |
Collapse
|
3
|
Sun B, Ni M, Tian S, Guo W, Cai S, Sondergaard MT, Chen Y, Mu Y, Estillore JP, Wang R, Chen J, Overgaard MT, Fill M, Ramos-Franco J, Nyegaard M, Wayne Chen SR. A gain-of-function mutation in the ITPR1 gating domain causes male infertility in mice. J Cell Physiol 2022; 237:3305-3316. [PMID: 35621185 DOI: 10.1002/jcp.30783] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Revised: 04/16/2022] [Accepted: 05/06/2022] [Indexed: 11/10/2022]
Abstract
Inositol 1,4,5-trisphosphate receptor 1 (ITPR1) is an intracellular Ca2+ release channel critical for numerous cellular processes. Despite its ubiquitous physiological significance, ITPR1 mutations have thus far been linked to primarily movement disorders. Surprisingly, most disease-associated ITPR1 mutations generate a loss of function. This leaves our understanding of ITPR1-associated pathology oddly one-sided, as little is known about the pathological consequences of ITPR1 gain of function (GOF). To this end, we generated an ITPR1 gating domain mutation (D2594K) that substantially enhanced the inositol trisphosphate (IP3 )-sensitivity of ITPR1, and a mouse model expressing this ITPR1-D2594K+/- GOF mutation. We found that heterozygous ITPR1-D2594K+/- mutant mice exhibited male infertility, azoospermia, and acrosome loss. Furthermore, we functionally characterized a human ITPR1 variant V494I identified in the UK Biobank database as potentially associated with disorders of the testis. We found that the ITPR1-V494I variant significantly enhanced IP3 -induced Ca2+ release in HEK293 cells. Thus, ITPR1 hyperactivity may increase the risk of testicular dysfunction.
Collapse
Affiliation(s)
- Bo Sun
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada.,Laboratory of Molecular Pharmacology, Medical School, Kunming University of Science and Technology, Kunming, China
| | - Mingke Ni
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Shanshan Tian
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Wenting Guo
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Shitian Cai
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Mads T Sondergaard
- Department of Chemistry and Bioscience, Aalborg University, Aalborg, Denmark
| | - Yongxiang Chen
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Yongxin Mu
- Department of Medicine, University of California at San Diego, La Jolla, California, USA
| | - John P Estillore
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Ruiwu Wang
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada
| | - Ju Chen
- Department of Medicine, University of California at San Diego, La Jolla, California, USA
| | - Michael T Overgaard
- Department of Chemistry and Bioscience, Aalborg University, Aalborg, Denmark
| | - Michael Fill
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois, USA
| | - Josefina Ramos-Franco
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois, USA
| | - Mette Nyegaard
- Department of Biomedicine, Aarhus University, Aarhus, Denmark.,Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Sui Rong Wayne Chen
- Department of Physiology and Pharmacology, Libin Cardiovascular Institute, University of Calgary, Calgary, Alberta, Canada.,Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois, USA
| |
Collapse
|
4
|
Blancard M, Touat-Hamici Z, Aguilar-Sanchez Y, Yin L, Vaksmann G, Roux-Buisson N, Fressart V, Denjoy I, Klug D, Neyroud N, Ramos-Franco J, Gomez AM, Guicheney P. A Type 2 Ryanodine Receptor Variant in the Helical Domain 2 Associated with an Impairment of the Adrenergic Response. J Pers Med 2021; 11:579. [PMID: 34202968 PMCID: PMC8235491 DOI: 10.3390/jpm11060579] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 06/16/2021] [Accepted: 06/16/2021] [Indexed: 11/17/2022] Open
Abstract
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is triggered by exercise or acute emotion in patients with normal resting electrocardiogram. The major disease-causing gene is RYR2, encoding the cardiac ryanodine receptor (RyR2). We report a novel RYR2 variant, p.Asp3291Val, outside the four CPVT mutation hotspots, in three CPVT families with numerous sudden deaths. This missense variant was first identified in a four-generation family, where eight sudden cardiac deaths occurred before the age of 30 in the context of adrenergic stress. All affected subjects harbored at least one copy of the RYR2 variant. Three affected sisters were homozygous for the variant. The same variant was found in two additional CPVT families. It is located in the helical domain 2 and changes a negatively charged amino acid widely conserved through evolution. Functional analysis of D3291V channels revealed a normal response to cytosolic Ca2+, a markedly reduced luminal Ca2+ sensitivity and, more importantly, an absence of normal response to 8-bromo-cAMP and forskolin stimulation in both transfected HEK293 and HL-1 cells. Our data support that the D3291V-RyR2 is a loss-of-function RyR2 variant responsible for an atypical form of CPVT inducing a mild dysfunction in basal conditions but leading potentially to fatal events through its unresponsiveness to adrenergic stimulation.
Collapse
Affiliation(s)
- Malorie Blancard
- Inserm, UMRS 1166, Institute of Cardiometabolism and Nutrition (ICAN), Sorbonne Université, 75013 Paris, France; (Z.T.-H.); (N.N.); (P.G.)
| | - Zahia Touat-Hamici
- Inserm, UMRS 1166, Institute of Cardiometabolism and Nutrition (ICAN), Sorbonne Université, 75013 Paris, France; (Z.T.-H.); (N.N.); (P.G.)
| | - Yuriana Aguilar-Sanchez
- Department of Physiology & Biophysics, Rush University Medical Center, Chicago, IL 60612, USA; (Y.A.-S.); (J.R.-F.)
| | - Liheng Yin
- Inserm, UMRS 1180, Université Paris Saclay, 92290 Châtenay-Malabry, France; (L.Y.); (A.M.G.)
| | - Guy Vaksmann
- Service de Cardiologie Pédiatrique, Hôpital Privé de la Louvière, 59042 Lille, France;
| | | | | | - Isabelle Denjoy
- Département de Cardiologie, Centre de Référence des Maladies Cardiaques Héréditaires, Hôpital Bichat, AP-HP, 75018 Paris, France;
| | - Didier Klug
- Hôpital Cardiologique, CHRU de Lille, 59000 Lille, France;
| | - Nathalie Neyroud
- Inserm, UMRS 1166, Institute of Cardiometabolism and Nutrition (ICAN), Sorbonne Université, 75013 Paris, France; (Z.T.-H.); (N.N.); (P.G.)
| | - Josefina Ramos-Franco
- Department of Physiology & Biophysics, Rush University Medical Center, Chicago, IL 60612, USA; (Y.A.-S.); (J.R.-F.)
| | - Ana Maria Gomez
- Inserm, UMRS 1180, Université Paris Saclay, 92290 Châtenay-Malabry, France; (L.Y.); (A.M.G.)
| | - Pascale Guicheney
- Inserm, UMRS 1166, Institute of Cardiometabolism and Nutrition (ICAN), Sorbonne Université, 75013 Paris, France; (Z.T.-H.); (N.N.); (P.G.)
| |
Collapse
|
5
|
Yin L, Zahradnikova A, Rizzetto R, Boncompagni S, Rabesahala de Meritens C, Zhang Y, Joanne P, Marqués-Sulé E, Aguilar-Sánchez Y, Fernández-Tenorio M, Villejoubert O, Li L, Wang YY, Mateo P, Nicolas V, Gerbaud P, Lai FA, Perrier R, Álvarez JL, Niggli E, Valdivia HH, Valdivia CR, Ramos-Franco J, Zorio E, Zissimopoulos S, Protasi F, Benitah JP, Gómez AM. Impaired Binding to Junctophilin-2 and Nanostructural Alteration in CPVT Mutation. Circ Res 2021; 129:e35-e52. [PMID: 34111951 DOI: 10.1161/circresaha.121.319094] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
[Figure: see text].
Collapse
Affiliation(s)
- Liheng Yin
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Alexandra Zahradnikova
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Riccardo Rizzetto
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Simona Boncompagni
- CAST, Department of Neuroscience, Imaging and Clinical Sciences (DNICS), Medicine and Ageing Sciences (DMSI), University Gabriele d'Annunzio, Chieti, Italy (S.B., F.P.)
| | | | - Yadan Zhang
- Swansea University Medical School, Institute of Life Science, Swansea, SA2 8PP, UK (C.R.d.M., Y.Z., S.Z.)
| | - Pierre Joanne
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Elena Marqués-Sulé
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.).,Physiotherapy, University of Valencia, Valencia, Spain (E.M.-S.)
| | - Yuriana Aguilar-Sánchez
- Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA (Y.A.-S., J.R.-F.)
| | | | - Olivier Villejoubert
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Linwei Li
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Yue Yi Wang
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Philippe Mateo
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | | | - Pascale Gerbaud
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - F Anthony Lai
- College of Medicine, Biomedical & Pharmaceutical Research Unit, QU Health, & Biomedical Research Centre, Qatar University, Doha, Qatar (F.A.L.)
| | | | - Julio L Álvarez
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.).,Institute of Cardiology, Havana, Cuba (J.L.A.)
| | - Ernst Niggli
- Physiology, University of Bern, Bern, Switzerland (M.F.-T., E.N.)
| | - Héctor H Valdivia
- Medicine and Cardiovascular Research Center, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin (H.H.V., C.R.V.)
| | - Carmen R Valdivia
- Medicine and Cardiovascular Research Center, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin (H.H.V., C.R.V.)
| | - Josefina Ramos-Franco
- Physiology and Biophysics, Rush University Medical Center, Chicago, IL, USA (Y.A.-S., J.R.-F.)
| | - Esther Zorio
- Cardiology Department and Unidad de Cardiopatías Familiares, Muerte Súbita y Mecanismos de Enfermedad (CaFaMuSMe), Hospital Universitario y Politécnico La Fe and Instituto de Investigación Sanitaria La Fe, Valencia, Spain (E.Z.).,Center for Biomedical Network Research on Cardiovascular diseases (CIBERCV), Madrid, Spain (E.Z.)
| | - Spyros Zissimopoulos
- Swansea University Medical School, Institute of Life Science, Swansea, SA2 8PP, UK (C.R.d.M., Y.Z., S.Z.)
| | - Feliciano Protasi
- CAST, Department of Neuroscience, Imaging and Clinical Sciences (DNICS), Medicine and Ageing Sciences (DMSI), University Gabriele d'Annunzio, Chieti, Italy (S.B., F.P.)
| | - Jean-Pierre Benitah
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| | - Ana M Gómez
- Signaling and Cardiovascular Pathophysiology - UMR-S 1180, Inserm, Université Paris-Saclay 92296 Châtenay-Malabry, France (L.Y., A.Z., R.R., P.J., E.M.-S., O.V., L.L., Y.Y.W., P.M., P.G., R.P., J.L.A., J.-P.B., A.M.G.)
| |
Collapse
|
6
|
Aguilar-Sanchez Y, Rodriguez de Yurre A, Argenziano M, Escobar AL, Ramos-Franco J. Transmural Autonomic Regulation of Cardiac Contractility at the Intact Heart Level. Front Physiol 2019; 10:773. [PMID: 31333477 PMCID: PMC6616252 DOI: 10.3389/fphys.2019.00773] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 06/03/2019] [Indexed: 01/14/2023] Open
Abstract
The relationship between cardiac excitability and contractility depends on when Ca2+ influx occurs during the ventricular action potential (AP). In mammals, it is accepted that Ca2+ influx through the L-type Ca2+ channels occurs during AP phase 2. However, in murine models, experimental evidence shows Ca2+ influx takes place during phase 1. Interestingly, Ca2+ influx that activates contraction is highly regulated by the autonomic nervous system. Indeed, autonomic regulation exerts multiple effects on Ca2+ handling and cardiac electrophysiology. In this paper, we explore autonomic regulation in endocardial and epicardial layers of intact beating mice hearts to evaluate their role on cardiac excitability and contractility. We hypothesize that in mouse cardiac ventricles the influx of Ca2+ that triggers excitation–contraction coupling (ECC) does not occur during phase 2. Using pulsed local field fluorescence microscopy and loose patch photolysis, we show sympathetic stimulation by isoproterenol increased the amplitude of Ca2+ transients in both layers. This increase in contractility was driven by an increase in amplitude and duration of the L-type Ca2+ current during phase 1. Interestingly, the β-adrenergic increase of Ca2+ influx slowed the repolarization of phase 1, suggesting a competition between Ca2+ and K+ currents during this phase. In addition, cAMP activated L-type Ca2+ currents before SR Ca2+ release activated the Na+-Ca2+ exchanger currents, indicating Cav1.2 channels are the initial target of PKA phosphorylation. In contrast, parasympathetic stimulation by carbachol did not have a substantial effect on amplitude and kinetics of endocardial and epicardial Ca2+ transients. However, carbachol transiently decreased the duration of the AP late phase 2 repolarization. The carbachol-induced shortening of phase 2 did not have a considerable effect on ventricular pressure and systolic Ca2+ dynamics. Interestingly, blockade of muscarinic receptors by atropine prolonged the duration of phase 2 indicating that, in isolated hearts, there is an intrinsic release of acetylcholine. In addition, the acceleration of repolarization induced by carbachol was blocked by the acetylcholine-mediated K+ current inhibition. Our results reveal the transmural ramifications of autonomic regulation in intact mice hearts and support our hypothesis that Ca2+ influx that triggers ECC occurs in AP phase 1 and not in phase 2.
Collapse
Affiliation(s)
- Yuriana Aguilar-Sanchez
- Department of Physiology and Biophysics, School of Medicine, Rush University Medical Center, Chicago, IL, United States
| | - Ainhoa Rodriguez de Yurre
- Laboratorio de Cardio Inmunologia, Instituto de Biofisica Carlos Chagas Filho, Rio de Janeiro, Brazil
| | - Mariana Argenziano
- Division of Human Genetics, Children's Hospital of Philadelphia, Philadelphia, PA, United States
| | - Ariel L Escobar
- Department of Bioengineering, School of Engineering, University of California, Merced, Merced, CA, United States
| | - Josefina Ramos-Franco
- Department of Physiology and Biophysics, School of Medicine, Rush University Medical Center, Chicago, IL, United States
| |
Collapse
|
7
|
Affiliation(s)
- Josefina Ramos-Franco
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL 60612
| | - Michael Fill
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL 60612
| |
Collapse
|
8
|
Ramos-Franco J, Aguilar-Sanchez Y, Escobar AL. Intact Heart Loose Patch Photolysis Reveals Ionic Current Kinetics During Ventricular Action Potentials. Circ Res 2015; 118:203-15. [PMID: 26565013 DOI: 10.1161/circresaha.115.307399] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Accepted: 11/12/2015] [Indexed: 12/16/2022]
Abstract
RATIONALE Assessing the underlying ionic currents during a triggered action potential (AP) in intact perfused hearts offers the opportunity to link molecular mechanisms with pathophysiological problems in cardiovascular research. The developed loose patch photolysis technique can provide striking new insights into cardiac function at the whole heart level during health and disease. OBJECTIVE To measure transmembrane ionic currents during an AP to determine how and when surface Ca(2+) influx that triggers Ca(2+)-induced Ca(2+) release occurs and how Ca(2+)-activated conductances can contribute to the genesis of AP phase 2. METHODS AND RESULTS Loose patch photolysis allows the measurement of transmembrane ionic currents in intact hearts. During a triggered AP, a voltage-dependent Ca(2+) conductance was fractionally activated (dis-inhibited) by rapidly photo-degrading nifedipine, the Ca(2+) channel blocker. The ionic currents during a mouse ventricular AP showed a fast early component and a slower late component. Pharmacological studies established that the molecular basis underlying the early component was driven by an influx of Ca(2+) through the L-type channel, CaV 1.2. The late component was identified as an Na(+)-Ca(2+) exchanger current mediated by Ca(2+) released from the sarcoplasmic reticulum. CONCLUSIONS The novel loose patch photolysis technique allowed the dissection of transmembrane ionic currents in the intact heart. We were able to determine that during an AP, L-type Ca(2+) current contributes to phase 1, whereas Na(+)-Ca(2+) exchanger contributes to phase 2. In addition, loose patch photolysis revealed that the influx of Ca(2+) through L-type Ca(2+) channels terminates because of voltage-dependent deactivation and not by Ca(2+)-dependent inactivation, as commonly believed.
Collapse
Affiliation(s)
- Josefina Ramos-Franco
- From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA
| | - Yuriana Aguilar-Sanchez
- From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA
| | - Ariel L Escobar
- From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA.
| |
Collapse
|
9
|
Ramos-Franco J, Aguilar-Sanchez Y, Escobar AL. Na-Ca Exchanger Current during the Cardiac Cycle in Intact Perfused Mouse Heart. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
|
10
|
Escobar AL, Perez CG, Reyes ME, Lucero SG, Kornyeyev D, Mejía-Alvarez R, Ramos-Franco J. Role of inositol 1,4,5-trisphosphate in the regulation of ventricular Ca(2+) signaling in intact mouse heart. J Mol Cell Cardiol 2012; 53:768-79. [PMID: 22960455 DOI: 10.1016/j.yjmcc.2012.08.019] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 07/25/2012] [Accepted: 08/23/2012] [Indexed: 11/27/2022]
Abstract
Inositol 1,4,5-trisphosphate (InsP(3)R)-mediated Ca(2+) signaling is a major pathway regulating multiple cellular functions in excitable and non-excitable cells. Although InsP(3)-mediated Ca(2+) signaling has been extensively described, its influence on ventricular myocardium activity has not been addressed in contracting hearts at the whole-organ level. In this work, InsP(3)-sensitive intracellular Ca(2+) signals were studied in intact hearts using laser scanning confocal microscopy and pulsed local-field fluorescence microscopy. Intracellular [InsP(3)] was rapidly increased by UV flash photolysis of membrane-permeant caged InsP(3). Our results indicate that the basal [Ca(2+)] increased after the flash photolysis of caged InsP(3) without affecting the action potential (AP)-induced Ca(2+) transients. The amplitude of the basal [Ca(2+)] elevation depended on the intracellular [InsP(3)] reached after the UV flash. Pretreatment with ryanodine failed to abolish the InsP(3)-induced Ca(2+) release (IICR), indicating that this response was not mediated by ryanodine receptors (RyR). Thapsigargin prevented Ca(2+) release from both RyR- and InsP(3)R-containing Ca(2+) stores, suggesting that these pools have similar Ca(2+) reuptake mechanisms. These results were reproduced in acutely isolated cells where photorelease of InsP(3) was able to induce changes in endothelial cells but not in AP-induced transients from cardiomyocytes. Taken together, these results suggest that IICR does not directly regulate cardiac excitation-contraction coupling. To our knowledge, this is the first demonstration of IICR in intact hearts. Consequently, our work provides a reference framework of the spatiotemporal attributes of the IICR under physiological conditions.
Collapse
Affiliation(s)
- Ariel L Escobar
- School of Engineering, University of California Merced, Merced, CA 95344, USA
| | | | | | | | | | | | | |
Collapse
|
11
|
Porta M, Zima AV, Nani A, Diaz-Sylvester PL, Copello JA, Ramos-Franco J, Blatter LA, Fill M. Single ryanodine receptor channel basis of caffeine's action on Ca2+ sparks. Biophys J 2011; 100:931-8. [PMID: 21320437 DOI: 10.1016/j.bpj.2011.01.017] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2010] [Revised: 01/03/2011] [Accepted: 01/10/2011] [Indexed: 10/18/2022] Open
Abstract
Caffeine (1, 3, 7-trimethylxanthine) is a widely used pharmacological agonist of the cardiac ryanodine receptor (RyR2) Ca(2+) release channel. It is also a well-known stimulant that can produce adverse side effects, including arrhythmias. Here, the action of caffeine on single RyR2 channels in bilayers and Ca(2+) sparks in permeabilized ventricular cardiomyocytes is defined. Single RyR2 caffeine activation depended on the free Ca(2+) level on both sides of the channel. Cytosolic Ca(2+) enhanced RyR2 caffeine affinity, whereas luminal Ca(2+) essentially scaled maximal caffeine activation. Caffeine activated single RyR2 channels in diastolic quasi-cell-like solutions (cytosolic MgATP, pCa 7) with an EC(50) of 9.0 ± 0.4 mM. Low-dose caffeine (0.15 mM) increased Ca(2+) spark frequency ∼75% and single RyR2 opening frequency ∼150%. This implies that not all spontaneous RyR2 openings during diastole are associated with Ca(2+) sparks. Assuming that only the longest openings evoke sparks, our data suggest that a spark may result only when a spontaneous single RyR2 opening lasts >6 ms.
Collapse
Affiliation(s)
- Maura Porta
- Department of Physiology, Midwestern University, Downers Grove, Illinois, USA
| | | | | | | | | | | | | | | |
Collapse
|
12
|
Qin J, Valle G, Nani A, Chen H, Ramos-Franco J, Nori A, Volpe P, Fill M. Ryanodine receptor luminal Ca2+ regulation: swapping calsequestrin and channel isoforms. Biophys J 2009; 97:1961-70. [PMID: 19804727 DOI: 10.1016/j.bpj.2009.07.030] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2009] [Revised: 07/10/2009] [Accepted: 07/21/2009] [Indexed: 11/20/2022] Open
Abstract
Sarcoplasmic reticulum (SR) Ca(2+) release in striated muscle is mediated by a multiprotein complex that includes the ryanodine receptor (RyR) Ca(2+) channel and the intra-SR Ca(2+) buffering protein calsequestrin (CSQ). Besides its buffering role, CSQ is thought to regulate RyR channel function. Here, CSQ-dependent luminal Ca(2+) regulation of skeletal (RyR1) and cardiac (RyR2) channels is explored. Skeletal (CSQ1) or cardiac (CSQ2) calsequestrin were systematically added to the luminal side of single RyR1 or RyR2 channels. The luminal Ca(2+) dependence of open probability (Po) over the physiologically relevant range (0.05-1 mM Ca(2+)) was defined for each of the four RyR/CSQ isoform pairings. We found that the luminal Ca(2+) sensitivity of single RyR2 channels was substantial when either CSQ isoform was present. In contrast, no significant luminal Ca(2+) sensitivity of single RyR1 channels was detected in the presence of either CSQ isoform. We conclude that CSQ-dependent luminal Ca(2+) regulation of single RyR2 channels lacks CSQ isoform specificity, and that CSQ-dependent luminal Ca(2+) regulation in skeletal muscle likely plays a relatively minor (if any) role in regulating the RyR1 channel activity, indicating that the chief role of CSQ1 in this tissue is as an intra-SR Ca(2+) buffer.
Collapse
Affiliation(s)
- Jia Qin
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois, USA
| | | | | | | | | | | | | | | |
Collapse
|
13
|
Snopko RM, Ramos-Franco J, Di Maio A, Karko KL, Manley C, Piedras-Rentería E, Mejía-Alvarez R. Ca2+ sparks and cellular distribution of ryanodine receptors in developing cardiomyocytes from rat. J Mol Cell Cardiol 2008; 44:1032-1044. [PMID: 18468619 DOI: 10.1016/j.yjmcc.2008.03.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2007] [Revised: 03/18/2008] [Accepted: 03/18/2008] [Indexed: 10/22/2022]
Abstract
Although abundant ryanodine receptors (RyRs) exist in cardiomyocytes from newborn (NB) rat and despite the maturity of their single-channel properties, the RyR contribution to excitation-contraction (E-C) coupling is minimal. Immature arrangement of RyRs in the Ca(2+) release site of the sarcoplasmic reticulum and/or distant RyRs location from the sarcolemmal Ca(2+) signal could explain this quiescence. Consequently, Ca(2+) sparks and their cellular distribution were studied in NB myocytes and correlated with the formation of dyads and transverse (T) tubules. Ca(2+) sparks were recorded in fluo-4-loaded intact ventricular myocytes acutely dissociated from adult and NB rats (0-9 days old). Sparks were defined/compared in the center and periphery of the cell. Co-immunolocalization of RyRs with dihydropyridine receptors (DHPR) was used to estimate dyad formation, while the development of T tubules was studied using di-8-ANEPPS and diIC12. Our results indicate that in NB cells, Ca(2+) sparks exhibited lower amplitude (1.7+/-0.5 vs. 3.6+/-1.7 F/F(0)), shorter duration (47+/-3.2 vs. 54.1+/-3 ms), and larger width (1.7+/-0.8 vs. 1.2+/-0.4 microm) than in adult. Although no significant changes were observed in the overall frequency, central sparks increased from approximately 60% at 0-1 day to 82% at 7-9 days. While immunolocalization revealed many central release sites at 7-8 days, fluorescence labeling of the plasma membrane showed less abundant internal T tubules. This could imply that although during the first week, release sites emerge forming dyads with DHPR-containing T tubules; some of these T tubules may not be connected to the surface, explaining the RyR quiescence during E-C coupling in NB.
Collapse
Affiliation(s)
- Rose M Snopko
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA
| | - Josefina Ramos-Franco
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612, USA
| | - Alessandro Di Maio
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Kimberly L Karko
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA
| | - Christopher Manley
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA
| | - Erika Piedras-Rentería
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA
| | - Rafael Mejía-Alvarez
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
| |
Collapse
|
14
|
Snopko RM, Aromolaran AS, Karko KL, Ramos-Franco J, Blatter LA, Mejía-Alvarez R. Cell culture modifies Ca2+ signaling during excitation-contraction coupling in neonate cardiac myocytes. Cell Calcium 2006; 41:13-25. [PMID: 16908061 DOI: 10.1016/j.ceca.2006.04.033] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Revised: 03/22/2006] [Accepted: 04/22/2006] [Indexed: 12/30/2022]
Abstract
In heart, the excitation-contraction coupling (ECC) mechanism changes during development. Primary cell culture has been used to study Ca(2+) signaling in newborn (NB) rat heart. In this work, the effects of cell culture on the action potential (AP) and ECC Ca(2+) signaling during development were investigated. Specifically, AP, Ca(2+) currents (I(Ca)), and ryanodine receptor (RyR) properties (i.e. density, distribution, and contribution to Ca(2+) transients and Ca(2+) sparks) were defined in cultured myocytes (CM) from 0-day-old NB rat at different times in culture (1-4 days). Compared with acutely dissociated myocytes (ADM) from NB of equivalent ages (1-4 days), CM showed lower RyR density (50% at 1 day, 25% at 4 days), but larger RyR contribution to the Ca(2+) transient (25% at 1 day, 57% at 4 days). Additionally, Ca(2+) sparks were larger, longer, wider, and more frequent in CM than in ADM. RyR cellular distribution also showed different arrangement. While in CM, RyRs were located peripherally, in ADM of equivalent ages a sarcomeric arrangement was predominant. Finally, CM showed a two-fold increase in sarcolemmal Ca(2+) entry during the AP. These results indicated that primary culture is a feasible model to study Ca(2+) signaling in heart; however, it does not precisely reproduce what occurs in ECC during development.
Collapse
Affiliation(s)
- Rose M Snopko
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, 2160 S. First Avenue, Maywood IL 60153, USA
| | | | | | | | | | | |
Collapse
|
15
|
Pérez CG, Copello JA, Li Y, Karko KL, Gómez L, Ramos-Franco J, Fill M, Escobar AL, Mejía-Alvarez R. Ryanodine receptor function in newborn rat heart. Am J Physiol Heart Circ Physiol 2005; 288:H2527-40. [PMID: 15626694 DOI: 10.1152/ajpheart.00188.2004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The role of ryanodine receptor (RyR) in cardiac excitation-contraction (E-C) coupling in newborns (NB) is not completely understood. To determine whether RyR functional properties change during development, we evaluated cellular distribution and functionality of sarcoplasmic reticulum (SR) in NB rats. Sarcomeric arrangement of immunostained SR Ca2+-ATPase (SERCA2a) and the presence of sizeable caffeine-induced Ca2+ transients demonstrated that functional SR exists in NB. E-C coupling properties were then defined in NB and compared with those in adult rats (AD). Ca2+ transients in NB reflected predominantly sarcolemmal Ca2+ entry, whereas the RyR-mediated component was ∼13%. Finally, the RyR density and functional properties at the single-channel level in NB were compared with those in AD. Ligand binding assays revealed that in NB, RyR density can be up to 36% of that found in AD, suggesting that some RyRs do not contribute to the Ca2+ transient. To test the hypothesis that RyR functional properties change during development, we incorporated single RyRs into lipid bilayers. Our results show that permeation and gating kinetics of NB RyRs are identical to those of AD. Also, endogenous ligands had similar effects on NB and AD RyRs: sigmoidal Ca2+ dependence, stronger Mg2+-induced inhibition at low cytoplasmic Ca2+ concentrations, comparable ATP-activating potency, and caffeine sensitivity. These observations indicate that NB rat heart contains fully functional RyRs and that the smaller contribution of RyR-mediated Ca2+ release to the intracellular Ca2+ transient in NB is not due to different single RyR channel properties or to the absence of functional intracellular Ca2+ stores.
Collapse
Affiliation(s)
- Claudia G Pérez
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois 60153, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Ramos J, Jung W, Ramos-Franco J, Mignery GA, Fill M. Single channel function of inositol 1,4,5-trisphosphate receptor type-1 and -2 isoform domain-swap chimeras. J Gen Physiol 2003; 121:399-411. [PMID: 12695486 PMCID: PMC2217376 DOI: 10.1085/jgp.200208718] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The InsP3R proteins have three recognized domains, the InsP3-binding, regulatory/coupling, and channel domains (Mignery, G.A., and T.C. Südhof. 1990. EMBO J. 9:3893-3898). The InsP3 binding domain and the channel-forming domain are at opposite ends of the protein. Ligand regulation of the channel must involve communication between these different regions of the protein. This communication likely involves the interceding sequence (i.e., the regulatory/coupling domain). The single channel functional attributes of the full-length recombinant type-1, -2, and -3 InsP3R channels have been defined. Here, two type-1/type-2 InsP3R regulatory/coupling domain chimeras were created and their single channel function defined. One chimera (1-2-1) contained the type-2 regulatory/coupling domain in a type-1 backbone. The other chimera (2-1-2) contained the type-1 regulatory/coupling domain in a type-2 backbone. These chimeric proteins were expressed in COS cells, isolated, and then reconstituted in proteoliposomes. The proteoliposomes were incorporated into artificial planar lipid bilayers and the single-channel function of the chimeras defined. The chimeras had permeation properties like that of wild-type channels. The ligand regulatory properties of the chimeras were altered. The InsP3 and Ca2+ regulation had some unique features but also had features in common with wild-type channels. These results suggest that different independent structural determinants govern InsP3R permeation and ligand regulation. It also suggests that ligand regulation is a multideterminant process that involves several different regions of the protein. This study also demonstrates that a chimera approach can be applied to define InsP3R structure-function.
Collapse
Affiliation(s)
- Jorge Ramos
- Department of Physiology, Loyola University Chicago, 2160 South First Avenue, Maywood, IL 60153, USA
| | | | | | | | | |
Collapse
|
17
|
Abstract
A full-length rat type 2 inositol 1,4,5-trisphosphate (InsP(3)) receptor cDNA construct was generated and expressed in COS-1 cells. Targeting of the full-length recombinant type 2 receptor protein to the endoplasmic reticulum was confirmed by immunocytochemistry using isoform specific affinity-purified antibodies and InsP(3)R-green fluorescent protein chimeras. The receptor protein was solubilized and incorporated into proteoliposomes for functional characterization. Single-channel recordings from proteoliposomes fused into planar lipid bilayers revealed that the recombinant protein formed InsP(3)- and Ca(2+)-sensitive ion channels. The unitary conductance ( approximately 250 pS; 220/20 mM Cs(+) as charge carrier), gating, InsP(3), and Ca(2+) sensitivities were similar to those previously described for the native type 2 InsP(3)R channel. However, the maximum open probability of the recombinant channel was slightly lower than that of its native counterpart. These data show that our full-length rat type 2 InsP(3)R cDNA construct encodes a protein that forms an ion channel with functional attributes like those of the native type 2 InsP(3)R channel. The possibility of measuring the function of single recombinant type 2 InsP(3)R is a significant step toward the use of molecular tools to define the determinants of isoform-specific InsP(3)R function and regulation.
Collapse
Affiliation(s)
- J Ramos-Franco
- Department of Physiology, Loyola University Chicago, Maywood, Illinois 60153 USA
| | | | | | | | | | | |
Collapse
|
18
|
Abstract
The inositol 1,4,5-trisphosphate receptor (InsP(3)R) forms ligand-regulated intracellular Ca(2+) release channels in the endoplasmic reticulum of all mammalian cells. The InsP(3)R has been suggested to have six transmembrane regions (TMRs) near its carboxyl terminus. A TMR-deletion mutation strategy was applied to define the location of the InsP(3)R pore. Mutant InsP(3)Rs were expressed in COS-1 cells and single channel function was defined in planar lipid bilayers. Mutants having the fifth and sixth TMR (and the interceding lumenal loop), but missing all other TMRs, formed channels with permeation properties similar to wild-type channels (gCs = 284; gCa = 60 pS; P(Ca)/P(Cs) = 6.3). These mutant channels bound InsP(3), but ligand occupancy did not regulate the constitutively open pore (P(o) > 0.80). We propose that a region of 191 amino acids (including the fifth and sixth TMR, residues 2398-2589) near the COOH terminus of the protein forms the InsP(3)R pore. Further, we have produced a constitutively open InsP(3)R pore mutant that is ideal for future site-directed mutagenesis studies of the structure-function relationships that define Ca(2+) permeation through the InsP(3)R channel.
Collapse
Affiliation(s)
- Josefina Ramos-Franco
- From the Department of Physiology, Loyola University Chicago, Maywood, Illinois 60153-5500
| | - Daniel Galvan
- From the Department of Physiology, Loyola University Chicago, Maywood, Illinois 60153-5500
| | - Gregory A. Mignery
- From the Department of Physiology, Loyola University Chicago, Maywood, Illinois 60153-5500
| | - Michael Fill
- From the Department of Physiology, Loyola University Chicago, Maywood, Illinois 60153-5500
| |
Collapse
|
19
|
Ramos-Franco J, Caenepeel S, Fill M, Mignery G. Single channel function of recombinant type-1 inositol 1,4,5-trisphosphate receptor ligand binding domain splice variants. Biophys J 1998; 75:2783-93. [PMID: 9826600 PMCID: PMC1299951 DOI: 10.1016/s0006-3495(98)77721-5] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
In this study we describe the expression and function of the two rat type-1 inositol 1,4,5-trisphosphate receptor (InsP3R) ligand binding domain splice variants (SI+/-/SII+). Receptor protein from COS-1 cells transfected with the type-1 InsP3R expression plasmids (pInsP3R-T1, pInsP3R-T1ALT) or control DNA were incorporated into planar lipid bilayers and the single channel properties of the recombinant receptors were defined. The unitary conductance of the two splice variants were approximately 290 pS with Cs+ as charge carrier and approximately 65 pS with Ca2+ as charge carrier. Both InsP3R expression products consistently behaved like those of the native type-1 receptor isoform isolated from cerebellum in terms of their InsP3, Ca2+, and heparin sensitivity. An InsP3 receptor ligand binding domain truncation lacking the 310 amino-terminal amino acids (pInsP3R-DeltaT1ALT) formed tetrameric complexes but failed to bind InsP3 with high affinity, and did not form functional Ca2+ channels when reconstituted in lipid bilayers. These data suggest that 1) the ligand binding alternative splice site is functionally inert in terms of InsP3 binding and single channel function, and 2) the single channel properties of the expressed recombinant type-1 channel are essentially identical to those of the native channel. This work establishes a foundation from which molecular/biophysical approaches can be used to define the structure-function properties of the InsP3 receptor channel family.
Collapse
Affiliation(s)
- J Ramos-Franco
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois 60153 USA
| | | | | | | |
Collapse
|
20
|
Abstract
The inositol 1,4,5-trisphosphate receptor (InsP3R) family of Ca2+ release channels is central to intracellular Ca2+ signaling in mammalian cells. The InsP3R channels release Ca2+ from intracellular compartments to generate localized Ca2+ transients that govern a myriad of cellular signaling phenomena (Berridge, 1993. Nature. 361:315-325; Joseph, 1996. Cell Signal. 8:1-7; Kume et al., 1997. Science. 278:1940-1943; Berridge, 1997. Nature. 368:759-760). express multiple InsP3R isoforms, but only the function of the single type 1 InsP3R channel is known. Here the single-channel function of single type 2 InsP3R channel is defined for the first time. The type 2 InsP3R forms channels with permeation properties similar to that of the type 1 receptor. The InsP3 regulation and Ca2+ regulation of type 1 and type 2 InsP3R channels are strikingly different. Both InsP3 and Ca2+ are more effective at activating single type 2 InsP3R, indicating that single type 2 channels mobilize substantially more Ca2+ than single type 1 channels in cells. Furthermore, high cytoplasmic Ca2+ concentrations inactivate type 1, but not type 2, InsP3R channels. This indicates that type 2 InsP3R channel is different from the type 1 channel in that its activity will not be inherently self-limiting, because Ca2+ passing through an active type 2 channel cannot feed back and turn the channel off. Thus the InsP3R identity will help define the spatial and temporal nature of local Ca2+ signaling events and may contribute to the segregation of parallel InsP3 signaling cascades in mammalian cells.
Collapse
Affiliation(s)
- J Ramos-Franco
- Loyola University Chicago, Stritch School of Medicine, Department of Physiology, and Cardiovascular Institute, Maywood, Illinois 60153 USA
| | | | | |
Collapse
|
21
|
Perez PJ, Ramos-Franco J, Fill M, Mignery GA. Identification and functional reconstitution of the type 2 inositol 1,4,5-trisphosphate receptor from ventricular cardiac myocytes. J Biol Chem 1997; 272:23961-9. [PMID: 9295347 DOI: 10.1074/jbc.272.38.23961] [Citation(s) in RCA: 125] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The inositol 1,4,5-trisphosphate receptor (InsP3R) is an intracellular Ca2+ release channel that mediates the rise in cytoplasmic calcium in response to receptor-activated production of InsP3. The InsP3R-mediated signaling pathway appears to be ubiquitous and is involved in many cellular processes including cell division, smooth muscle contraction, and neuronal signaling. Different regions of the heart also express InsP3 receptors. We report here that acutely dissociated ventricular myocytes from ferret and rat hearts express significant levels of InsP3R as indicated by immunoblotting with a receptor consensus antibody. InsP3 binding experiments (KD = 23.6 nM and Bmax = 0.46 pmol/mg) suggest the myocytes contain the high affinity type 2 InsP3 receptor. Exhaustive mRNA screening by polymerase chain reaction, RNase protection, and subsequent DNA sequencing positively identify the InsP3R as type 2. The type 2 receptor from ferret heart was then incorporated into planar lipid bilayers and formed Ca2+-selective, InsP3-activated, heparin-blocked ion channels. We conclude that the predominant InsP3 receptor isoform expressed in cardiac myocytes is type 2 and that it forms a functional InsP3-gated Ca2+ channel when reconstituted in planar lipid bilayers.
Collapse
Affiliation(s)
- P J Perez
- Department of Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois 60153, USA
| | | | | | | |
Collapse
|
22
|
Abstract
Platelet-activating factor (PAF), a potent signaling lipid implicated as a mediator of pathological responses, has both negative chronotropic and inotropic effects on the heart, although the mechanism(s) involved is not well defined. Because activation of the muscarinic acetylcholine-activated K+ current (IK(ACh)) also produces a negative chronotropic and inotropic response in myocardium, this study examines whether PAF has effects on IK(ACh) in isolated bullfrog atrial myocytes under whole-cell voltage-clamp conditions. We find that 2 microM PAF increases the rate of GTP-gamma-S-mediated IK(ACh) activation (from 0.30 +/- 0.01 min-1 [n = 20] to 0.73 +/- 0.07 min-1 [n = 12], p < 0.005, in the absence of acetylcholine). This effect of 2 microM PAF was blocked by the PAF antagonist CV-3988 (5 microM, 0.33 +/- 0.14 min-1 [n = 12]), suggesting the presence of specific PAF receptors coupled to IK(ACh) activation. Further support for mediation by specific G protein-coupled PAF receptors derives from the inability of PAF to modulate IK(ACh) after maximal activation in the presence of GTP-gamma-S. Eicosatetraynoic acid (ETYA, an inhibitor of 5- and 12-lipoxygenases) did not prevent the PAF-mediated increase in the rate of IK(ACh) activation (10 microM ETYA, 0.28 +/- 0.03 min-1 [n = 7]; 10 microM ETYA plus 2 microM PAF, 0.58 +/- 0.13 min-1 [n = 8]; p < 0.05), suggesting that the observed PAF effect is not mediated by increases in arachidonic acid metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- J Ramos-Franco
- Department of Physiology, School of Medicine, Johns Hopkins University, Baltimore, MD 21205
| | | | | |
Collapse
|
23
|
Abstract
The regulation of calcium-activated K (KCa) channels by a G protein-mediated mechanism was studied. KCa channels were reconstituted in planar lipid bilayers by fusion of membrane vesicles from rat or pig myometrium. The regulatory process was studied by exploring the actions of GTP and GTP gamma S on single channel activity. KCa channels had a conductance of 260 +/- 6 pS (n = 25, +/- SE, 250/50 mM KCl gradient) and were voltage dependent. The open probability (Po) vs. voltage relationships were well fit by a Boltzmann distribution. The slope factor (11 mV) was insensitive to internal Ca2+. The half activation potential (V1/2) was shifted -70 mV by raising internal Ca2+ from pCa 6.2 to pCa 4. Addition of GTP or GTP gamma S activated channel activity only in the presence of Mg2+, a characteristic typical of G protein-mediated mechanisms. The Po increased from 0.18 +/- 0.08 to 0.49 +/- 0.07 (n = 7, 0 mV, pCa 6 to 6.8). The channel was also activated (Po increased from 0.03 to 0.37) in the presence of AMP-PNP, a nonphosphorylating ATP analogue, suggesting a direct G protein gating of KCa channels. Upon nucleotide activation, mean open time increased by a factor of 2.7 +/- 0.7 and mean closed time decreased by 0.2 +/- 0.07 of their initial values (n = 6). Norepinephrine (NE) or isoproterenol potentiated the GTP-mediated activation of KCa channels (Po increased from 0.17 +/- 0.06 to 0.35 +/- 0.07, n = 10). These results suggest that myometrium possesses beta-adrenergic receptors coupled to a GTP-dependent protein that can directly gate KCa channels. Furthermore, KCa channels, beta-adrenergic receptors, and G proteins can be reconstituted in lipid bilayers as a stable, functionally coupled, molecular complex.
Collapse
Affiliation(s)
- L Toro
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030
| | | | | |
Collapse
|