High Time Resolution Analysis of Voltage-Dependent and Voltage-Independent Calcium Sparks in Frog Skeletal Muscle Fibers
In amphibian skeletal muscle calcium (Ca2+) sparks occur both as voltage-dependent and voltage-independent ligand-activated release events. However, whether their properties and their origin show similarities are still in debate. Elevated K+, constant Cl– content solutions were used to initiate smal...
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Frontiers Media S.A.
2020-12-01
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| Series: | Frontiers in Physiology |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fphys.2020.599822/full |
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| author | Henrietta Cserne Szappanos Henrietta Cserne Szappanos János Vincze Dóra Bodnár Beatrix Dienes Martin F. Schneider László Csernoch Péter Szentesi |
| author_facet | Henrietta Cserne Szappanos Henrietta Cserne Szappanos János Vincze Dóra Bodnár Beatrix Dienes Martin F. Schneider László Csernoch Péter Szentesi |
| author_sort | Henrietta Cserne Szappanos |
| collection | DOAJ |
| description | In amphibian skeletal muscle calcium (Ca2+) sparks occur both as voltage-dependent and voltage-independent ligand-activated release events. However, whether their properties and their origin show similarities are still in debate. Elevated K+, constant Cl– content solutions were used to initiate small depolarizations of the resting membrane potential to activate dihydropyridine receptors (DHPR) and caffeine to open ryanodine receptors (RyR) on intact fibers. The properties of Ca2+ sparks observed under control conditions were compared to those measured on depolarized cells and those after caffeine treatment. Calcium sparks were recorded on intact frog skeletal muscle fibers using high time resolution confocal microscopy (x-y scan: 30 Hz). Sparks were elicited by 1 mmol/l caffeine or subthreshold depolarization to different membrane potentials. Both treatments increased the frequency of sparks and altered their morphology. Images were analyzed by custom-made computer programs. Both the amplitude (in ΔF/F0; 0.259 ± 0.001 vs. 0.164 ± 0.001; n = 24942 and 43326, respectively; mean ± SE, p < 0.001) and the full width at half maximum (FWHM, in μm; parallel with fiber axis: 2.34 ± 0.01 vs. 1.92 ± 0.01, p < 0.001; perpendicular to fiber axis: 2.08 ± 0.01 vs. 1.68 ± 0.01, p < 0.001) of sparks was significantly greater after caffeine treatment than on depolarized cells. 9.8% of the sparks detected on depolarized fibers and about one third of the caffeine activated sparks (29.7%) overlapped with another one on the previous frame on x-y scans. Centre of overlapping sparks travelled significantly longer distances between consecutive frames after caffeine treatment then after depolarization (in μm; 1.66 ± 0.01 vs. 0.95 ± 0.01, p < 0.001). Our results suggest that the two types of ryanodine receptors, the junctional RyRs controlled by DHPRs and the parajunctional RyRs are activated independently, using alternate ways, with the possibility of cooperation between neighboring release channels. |
| first_indexed | 2024-12-14T04:16:02Z |
| format | Article |
| id | doaj.art-ff6e5e6b8cb841cd8fd95f9b3d1e5747 |
| institution | Directory Open Access Journal |
| issn | 1664-042X |
| language | English |
| last_indexed | 2024-12-14T04:16:02Z |
| publishDate | 2020-12-01 |
| publisher | Frontiers Media S.A. |
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| series | Frontiers in Physiology |
| spelling | doaj.art-ff6e5e6b8cb841cd8fd95f9b3d1e57472022-12-21T23:17:33ZengFrontiers Media S.A.Frontiers in Physiology1664-042X2020-12-011110.3389/fphys.2020.599822599822High Time Resolution Analysis of Voltage-Dependent and Voltage-Independent Calcium Sparks in Frog Skeletal Muscle FibersHenrietta Cserne Szappanos0Henrietta Cserne Szappanos1János Vincze2Dóra Bodnár3Beatrix Dienes4Martin F. Schneider5László Csernoch6Péter Szentesi7Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, Baltimore, MD, United StatesDepartment of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, HungaryDepartment of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, HungaryDepartment of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, HungaryDepartment of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, HungaryDepartment of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, Baltimore, MD, United StatesDepartment of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, HungaryDepartment of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, HungaryIn amphibian skeletal muscle calcium (Ca2+) sparks occur both as voltage-dependent and voltage-independent ligand-activated release events. However, whether their properties and their origin show similarities are still in debate. Elevated K+, constant Cl– content solutions were used to initiate small depolarizations of the resting membrane potential to activate dihydropyridine receptors (DHPR) and caffeine to open ryanodine receptors (RyR) on intact fibers. The properties of Ca2+ sparks observed under control conditions were compared to those measured on depolarized cells and those after caffeine treatment. Calcium sparks were recorded on intact frog skeletal muscle fibers using high time resolution confocal microscopy (x-y scan: 30 Hz). Sparks were elicited by 1 mmol/l caffeine or subthreshold depolarization to different membrane potentials. Both treatments increased the frequency of sparks and altered their morphology. Images were analyzed by custom-made computer programs. Both the amplitude (in ΔF/F0; 0.259 ± 0.001 vs. 0.164 ± 0.001; n = 24942 and 43326, respectively; mean ± SE, p < 0.001) and the full width at half maximum (FWHM, in μm; parallel with fiber axis: 2.34 ± 0.01 vs. 1.92 ± 0.01, p < 0.001; perpendicular to fiber axis: 2.08 ± 0.01 vs. 1.68 ± 0.01, p < 0.001) of sparks was significantly greater after caffeine treatment than on depolarized cells. 9.8% of the sparks detected on depolarized fibers and about one third of the caffeine activated sparks (29.7%) overlapped with another one on the previous frame on x-y scans. Centre of overlapping sparks travelled significantly longer distances between consecutive frames after caffeine treatment then after depolarization (in μm; 1.66 ± 0.01 vs. 0.95 ± 0.01, p < 0.001). Our results suggest that the two types of ryanodine receptors, the junctional RyRs controlled by DHPRs and the parajunctional RyRs are activated independently, using alternate ways, with the possibility of cooperation between neighboring release channels.https://www.frontiersin.org/articles/10.3389/fphys.2020.599822/fullskeletal musclefrogexcitation-contraction couplingryanodine receptorcalcium-induced calcium releasemembrane depolarization |
| spellingShingle | Henrietta Cserne Szappanos Henrietta Cserne Szappanos János Vincze Dóra Bodnár Beatrix Dienes Martin F. Schneider László Csernoch Péter Szentesi High Time Resolution Analysis of Voltage-Dependent and Voltage-Independent Calcium Sparks in Frog Skeletal Muscle Fibers Frontiers in Physiology skeletal muscle frog excitation-contraction coupling ryanodine receptor calcium-induced calcium release membrane depolarization |
| title | High Time Resolution Analysis of Voltage-Dependent and Voltage-Independent Calcium Sparks in Frog Skeletal Muscle Fibers |
| title_full | High Time Resolution Analysis of Voltage-Dependent and Voltage-Independent Calcium Sparks in Frog Skeletal Muscle Fibers |
| title_fullStr | High Time Resolution Analysis of Voltage-Dependent and Voltage-Independent Calcium Sparks in Frog Skeletal Muscle Fibers |
| title_full_unstemmed | High Time Resolution Analysis of Voltage-Dependent and Voltage-Independent Calcium Sparks in Frog Skeletal Muscle Fibers |
| title_short | High Time Resolution Analysis of Voltage-Dependent and Voltage-Independent Calcium Sparks in Frog Skeletal Muscle Fibers |
| title_sort | high time resolution analysis of voltage dependent and voltage independent calcium sparks in frog skeletal muscle fibers |
| topic | skeletal muscle frog excitation-contraction coupling ryanodine receptor calcium-induced calcium release membrane depolarization |
| url | https://www.frontiersin.org/articles/10.3389/fphys.2020.599822/full |
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