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Olivera JF, Pizarro G. Quantal Properties of Voltage-Dependent Ca 2+ Release in Frog Skeletal Muscle Persist After Reduction of [Ca 2+] in the Sarcoplasmic Reticulum. J Membr Biol 2024; 257:37-50. [PMID: 38460011 DOI: 10.1007/s00232-024-00309-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Accepted: 02/09/2024] [Indexed: 03/11/2024]
Abstract
In skeletal muscle, the Ca2+ release flux elicited by a voltage clamp pulse rises to an early peak that inactivates rapidly to a much lower steady level. Using a double pulse protocol the fast inactivation follows an arithmetic rule: if the conditioning depolarization is less than or equal to the test depolarization, then decay (peak minus steady level) in the conditioning release is approximately equal to suppression (unconditioned minus conditioned peak) of the test release. This is due to quantal activation by voltage, analogous to the quantal activation of IP3 receptor channels. Two mechanisms are possible. One is the existence of subsets of channels with different sensitivities to voltage. The other is that the clusters of Ca2+-gated Ryanodine Receptor (RyR) β in the parajunctional terminal cisternae might constitute the quantal units. These Ca2+-gated channels are activated by the release of Ca2+ through the voltage-gated RyR α channels. If the RyR β were at the basis of quantal release, it should be modified by strong inhibition of the primary voltage-gated release. This was attained in two ways, by sarcoplasmic reticulum (SR) Ca2+ depletion and by voltage-dependent inactivation. Both procedures reduced global Ca2+ release flux, but SR Ca2+ depletion reduced the single RyR current as well. The effect of both interventions on the quantal properties of Ca2+ release in frog skeletal muscle fibers were studied under voltage clamp. The quantal properties of release were preserved regardless of the inhibitory maneuver applied. These findings put a limit on the role of the Ca2+-activated component of release in generating quantal activation.
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Affiliation(s)
- J F Olivera
- Departamento de Biofísica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay
| | - G Pizarro
- Departamento de Biofísica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
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Zhu J, Fan Y, Lu Q, Yang Y, Li H, Liu X, Zhang H, Sun B, Liu Q, Zhao J, Yang Z, Li L, Feng H, Xu J. Increased transient receptor potential canonical 3 activity is involved in the pathogenesis of detrusor overactivity by dynamic interaction with Na +/Ca 2+ exchanger 1. J Transl Med 2022; 102:48-56. [PMID: 34497367 DOI: 10.1038/s41374-021-00665-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 08/15/2021] [Accepted: 08/16/2021] [Indexed: 11/08/2022] Open
Abstract
Transient receptor potential canonical 3 (TRPC3) is a nonselective cation channel, and its dysfunction is the basis of many clinical diseases. However, little is known about its possible role in the bladder. The purpose of this study was to explore the function and mechanism of TRPC3 in partial bladder outlet obstruction (PBOO)-induced detrusor overactivity (DO). We studied 31 adult female rats with DO induced by PBOO (the DO group) and 40 sham-operated rats (the control group). Here we report that the expression of TRPC3 in the bladder of DO rats increased significantly. Furthermore, PYR10, which can selectively inhibit the TRPC3 channel, significantly reduced bladder excitability in DO and control rats, but the decrease of the bladder excitability of DO rats was more obvious. PYR10 significantly reduced the intracellular calcium concentration in smooth muscle cells (SMCs) in DO and control rats. Finally, Na+/Ca2+ exchanger 1 (NCX1) colocalizes with TRPC3 and affects its expression and function. Collectively, these results indicate that TRPC3 plays an important role in the pathogenesis of DO through a synergistic effect with NCX1. TRPC3 and NCX1 may be new therapeutic targets for DO.
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Affiliation(s)
- Jingzhen Zhu
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Yi Fan
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Qudong Lu
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Yang Yang
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Hui Li
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Xin Liu
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Hengshuai Zhang
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Bishao Sun
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Qian Liu
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Jiang Zhao
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Zhenxing Yang
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Longkun Li
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China
| | - Huan Feng
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China.
| | - Jie Xu
- Department of Urology, Second Affiliated Hospital, Army Medical University, Chongqing, China.
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Milán AF, Rincón OA, Arango LB, Reutovich AA, Smith GL, Giraldo MA, Bou-Abdallah F, Calderón JC. Calibration of mammalian skeletal muscle Ca 2+ transients recorded with the fast Ca 2+ dye Mag-Fluo-4. Biochim Biophys Acta Gen Subj 2021; 1865:129939. [PMID: 34082059 DOI: 10.1016/j.bbagen.2021.129939] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 05/12/2021] [Accepted: 05/25/2021] [Indexed: 10/21/2022]
Abstract
BACKGROUND Mag-Fluo-4 is increasingly employed for studying Ca2+ signaling in skeletal muscle; however, the lack of information on the Ca2+-Mag-Fluo-4 reaction limits its wider usage. METHODS Fluorescence and isothermal titration calorimetry (ITC) experiments were performed to determine the binding stoichiometry (n) and thermodynamics (enthalpy (ΔH) and entropy (ΔS) changes), as well as the in vitro and in situ Kd of the Ca2+-Mag-Fluo-4 reaction. Rate constants (kon, koff), fluorescence maximum (Fmax), minimum (Fmin), and the dye compartmentalization were also estimated. Experiments in cells used enzymatically dissociated flexor digitorum brevis fibres of C57BL6, adult mice, loaded at room temperature for 8 min, with 6 μM Mag-Fluo-4, AM, and permeabilized with saponin or ionomycin. All measurements were done at 20 °C. RESULTS The in vitro fluorescence assays showed a binding stoichiometry of 0.5 for the Ca2+/Mag-Fluo-4 (n = 5) reaction. ITC results (n = 3) provided ΔH and ΔS values of 2.3 (0.7) kJ/mol and 97.8 (5.9) J/mol.K, respectively. The in situ Kd was 1.652 × 105μM2(n = 58 fibres, R2 = 0.99). With an Fmax of 150.9 (8.8) A.U. (n = 8), Fmin of 0.14 (0.1) A.U. (n = 10), and ΔF of Ca2+ transients of 8.4 (2.5) A.U. (n = 10), the sarcoplasmic [Ca2+]peak reached 22.5 (7.8) μM. Compartmentalized dye amounted to only 1.1 (0.7)% (n = 10). CONCLUSIONS Two Mag-Fluo-4 molecules coalesce around one Ca2+ ion, in an entropy-driven, very low in situ affinity reaction, making it suitable to reliably track the kinetics of rapid muscle Ca2+ transients. GENERAL SIGNIFICANCE Our results may be relevant to the quantitative study of Ca2+ kinetics in many other cell types.
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Affiliation(s)
- Andrés F Milán
- Physiology and Biochemistry Research Group-PHYSIS, Faculty of Medicine, University of Antioquia, Medellin, Colombia
| | - Oscar A Rincón
- Biophysics Group, Institute of Physics, University of Antioquia, Medellin, Colombia
| | - Leidy B Arango
- Physiology and Biochemistry Research Group-PHYSIS, Faculty of Medicine, University of Antioquia, Medellin, Colombia
| | - Aliaksandra A Reutovich
- Department of Chemistry, The State University of New York at Potsdam (SUNY Potsdam), New York, NY, USA
| | - Gideon L Smith
- Department of Chemistry, The State University of New York at Potsdam (SUNY Potsdam), New York, NY, USA
| | - Marco A Giraldo
- Biophysics Group, Institute of Physics, University of Antioquia, Medellin, Colombia
| | - Fadi Bou-Abdallah
- Department of Chemistry, The State University of New York at Potsdam (SUNY Potsdam), New York, NY, USA.
| | - Juan C Calderón
- Physiology and Biochemistry Research Group-PHYSIS, Faculty of Medicine, University of Antioquia, Medellin, Colombia.
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A new set of equations for the simplified calibration of fluorescence Ca 2+ transients in skeletal muscle fibers. J Muscle Res Cell Motil 2021; 42:161-168. [PMID: 33595763 DOI: 10.1007/s10974-021-09597-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Accepted: 01/18/2021] [Indexed: 12/26/2022]
Abstract
The classical approach for calibrating non-ratiometric fluorescent Ca2+ dyes entails the measurement of the fluorescence maximum (Fmax) and minimum (Fmin), as well as the dissociation constant (Kd) of the Ca2+-Dye reaction (model 1). An alternative equation does not need the Fmin but requires the rate constants kon and koff (model 2). However, both approaches are experimentally time consuming and the rate constants for several dyes are unknown. Here, we propose a set of equations (model 3) that simplify the calibration of fluorescent Ca2+ transients obtained with non-ratiometric dyes. This equation allows the calibration of signals without using the Fmin: [Ca2+] = Kd(F - Frest/Fmax - F) + [Ca2+]IR(Fmax - Frest/Fmax - F), where [Ca2+]IR is the resting [Ca2+]. If the classical calibration approach is followed, the Fmin can be estimated from: Fmin = Frest - ([Ca2+]IR(Fmax - Frest)/Kd). We tested the models' performance using signals obtained from enzymatically dissociated flexor digitorum brevis fibers of C57BL/6 mice loaded with Fluo-4, AM. Model 3 performed the same as model 2, and both gave peak [Ca2+] values 15 ± 0.3% (n = 3) lower than model 1, when we used our experimental Fmin (1.24 ± 0.11 A.U., n = 4). However, when we used the mathematically estimated Fmin (6.78 ± 0.2 A.U) for model 1, the peak [Ca2+] were similar for all three models. This suggests that the dye leakage makes a correct determination of the Fmin unlikely and induces errors in the estimation of [Ca2+]. In conclusion, we propose simpler and time-saving equations that help to reliably calibrate cytosolic Ca2+ transients obtained with non-ratiometric fluorescent dyes. The use of the estimated Fmin avoids the uncertainties associated with its experimental measurement.
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Pizarro G, Olivera JF. The dynamics of Ca 2+ within the sarcoplasmic reticulum of frog skeletal muscle. A simulation study. J Theor Biol 2020; 504:110371. [PMID: 32533961 DOI: 10.1016/j.jtbi.2020.110371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Revised: 06/08/2020] [Accepted: 06/08/2020] [Indexed: 10/24/2022]
Abstract
In skeletal muscle, Ca2+ release from the sarcoplasmic reticulum (SR) triggers contraction. In this study we develop a two compartment model to account for the Ca2+ dynamics in frog skeletal muscle fibers. The two compartments in the model correspond to the SR and the cytoplasm, where the myofibrils are placed. We use a detailed model for the several Ca2+ binding proteins in the cytoplasm in line with previous models. As a new feature, Ca2+ binding sites within the SR, attributed to calsequestrin, are modeled based on experimentally obtained properties. The intra SR Ca2+ buffer shows cooperativity, well represented by a Hill equation with parameters that depend on the initial [Ca2+] in the SR ([Ca2+]SR). The number of total sites as well as the [Ca2+]SR of half saturation are reduced as the resting [Ca2+]SR is reduced, on the other hand the Hill number is not changed. The buffer power remained roughly constant. The release process is activated by a voltage dependent mechanism that increases the Ca2+ permeability of the SR. We use the permeability time course and amplitude experimentally obtained during a voltage clamp pulse to drive the simulations. This model successfully reproduces the SR and cytoplasmic transients observed. Additionally, we simulate [Ca2+] SR transients in the case of high concentration of extrinsic Ca2+ buffers added to the cytoplasm to explore what properties of the permeability are necessary to account for the experimentally observed [Ca2+]SR transients. The main novelty of the model, the intra SR Ca2+ buffer, is crucial for reproducing the experimental observations and it would be of use in future theoretical studies of excitation contraction coupling in skeletal muscle.
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Affiliation(s)
- Gonzalo Pizarro
- Departamento de Biofísica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay. Gral. Flores 2125, Montevideo, CP11800, Uruguay.
| | - J Fernando Olivera
- Departamento de Biofísica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay. Gral. Flores 2125, Montevideo, CP11800, Uruguay.
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Ca 2+-induced sarcoplasmic reticulum Ca 2+ release in myotubularin-deficient muscle fibers. Cell Calcium 2019; 80:91-100. [PMID: 30999217 DOI: 10.1016/j.ceca.2019.04.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 03/27/2019] [Accepted: 04/08/2019] [Indexed: 11/23/2022]
Abstract
Skeletal muscle deficiency in the 3-phosphoinositide (PtdInsP) phosphatase myotubularin (MTM1) causes myotubular myopathy which is associated with severe depression of voltage-activated sarcoplasmic reticulum Ca2+ release through ryanodine receptors. In the present study we aimed at further understanding how Ca2+ release is altered in MTM1-deficient muscle fibers, at rest and during activation. While in wild-type muscle fibers, SR Ca2+ release exhibits fast stereotyped kinetics of activation and decay throughout the voltage range of activation, Ca2+ release in MTM1-deficient muscle fibers exhibits slow and unconventional kinetics at intermediate voltages, suggestive of partial loss of the normal control of ryanodine receptor Ca2+ channel activity. In addition, the diseased muscle fibers at rest exhibit spontaneous elementary Ca2+ release events at a frequency 30 times greater than that of control fibers. Eighty percent of the events have spatiotemporal properties of archetypal Ca2+ sparks while the rest take either the form of lower amplitude, longer duration Ca2+ release events or of a combination thereof. The events occur at preferred locations in the fibers, indicating spatially uneven distribution of the parameters determining spontaneous ryanodine receptor 1 opening. Spatially large Ca2+ release sources were obviously involved in some of these events, suggesting that opening of ryanodine receptors in one cluster can activate opening of ryanodine receptors in a neighboring one. Overall results demonstrate that opening of Ca2+-activated ryanodine receptors is promoted both at rest and during excitation-contraction coupling in MTM1-deficient muscle fibers. Because access to this activation mode is denied to ryanodine receptors in healthy skeletal muscle, this may play an important role in the associated disease situation.
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