Single Ca Research Articles

Abstract 765: Sex Difference in Cardiomyocyte Functional Etiology in Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) accounts for >50% of heart failure patients and is particularly prevalent in women. A mechanistic understanding of the intrinsic cardiomyocyte pathology in HFpEF is limited with no selective treatments identified. Gender-specific aspects of HFpEF etiology have not been well characterized. The aim of this study was to experimentally evaluate sex difference in cardiac and cardiomyocyte performance in HFpEF, using a novel recently developed rodent model of HFpEF - the ‘Hypertrophic Heart Rat’. Echocardiography was performed in 50 week male and female HHR/NHR (Normal Heart Rat) using a GE Vivid 9. Fibrosis measurements employed picrosirius red staining. Single myocyte force, shortening and intracellular Ca 2+ measurements were obtained (Myostretcher, Ionoptix). Male and female HHR hearts were hypertrophic (M: 4.9±0.3 vs 3.7±0.1; F: 6.6±0.5 vs 4.4±0.1mg/g CWI) with significant diastolic dysfunction (M:27.8±1.4 vs 18.0±1.7; F: 28.9±1.2 vs 18.9±1.0 E/E’) and preserved systolic function (M:78.4±1.9 vs 74.5±1.3; F: 80.9±1.3 vs 78.1±0.8 EF). Female HHR, but not males, exhibited diffuse interstitial fibrosis (M: 3.33±0.1 vs 3.51±0.1; F: 11.45±0.4 vs 8.44±0.2%). In male, but not female, cardiomyocytes, hypercontractility and high cytosolic operational Ca 2+ levels were observed (64% and 116% increase respectively). The force-length gradient produced by serial stretches of isolated cardiomyocytes was increased in male and female HHR (M:6.8±0.4 vs 4.3±0.8; F: 7.4±0.5 vs 3.0±0.4 nN/%SL stretch) indicating stiffer cardiomyocytes in the HFpEF hearts. The increase in stiffness was significantly accentuated in females. This study indicates that in HFpEF the cardiomyocyte functional etiology is different in males and females. Whilst in males the relationship between cardiomyocyte hypercontractility is the most prominent characteristic of HFpEF, in females the remodelling of the extracellular matrix exacerbates instrinsic myocyte stiffness. Further investigation of the molecular pathways involved in these processes is required for identification of potential therapeutic targets.

Impact of road deicing salts on the Upper Passaic River Basin, New Jersey: a geochemical analysis of the major ions in groundwater

Road deicing salts, primarily sodium chloride, has been used widely to remove snow and ice from roadways in New Jersey and the northern United States since the 1950s. Currently, New Jersey stores up to 141 million kg of rock salt and 2401 m3 of liquid calcium chloride in the winter season for road deicing. Road deicing helps to reduce accident rates, road delays, and to improve road accessibility. While it is known that the use of road deicers is beneficial, road salts have also been shown to affect surface water and groundwater quality. In this study, an analysis of major ion concentration of groundwater collected by the United States Geological Survey (USGS) for the Upper Passaic River Basin (UPRB) was carried out. The UPRB has a large area of urban land use and a number of significant roads that are regularly deiced during the winter. The results of the study have shown that the contribution of Cl− to the TDS of groundwater increased significantly by the 2000s. Decadal bivariate plots of Na+ vs Cl− and Cl− vs TDS showed a strong increase in the correlations between these ions from the 1960s to the 2000s. Bivariate plots of Na+ vs Cl− and Ca2+ vs Mg2+ display a strong correlation, while those of Na+ vs Ca2+ and Cl− vs Ca2+ display a poor correlation. These observations suggest a link between Na+, Cl− and TDS, a link between Ca2+ and Mg2+, and no link between Ca2+ and Cl−, and between Ca2+ and Na+. Plots of Piper diagrams show that the groundwater facies have changed through time, starting as a single Ca(HCO3)2 species and shifting gradually towards a NaCl-dominated species. Plots of individual ion concentrations versus specific conductance show an increase in Na+ and Cl− over time and point towards an external influx of these ions. In general, groundwater in the UPRB is fresh with total dissolved solids less than 500 mg/L. Against the natural groundwater evolutionary trend, chloride is found to dominate over other chemical species in this freshwater system. These results provide evidence of a link between groundwater chlorides and road deicing salts in the UPRB.

A novel Ca2+-binding protein that can rapidly transduce auxin responses during root growth.

Signaling cross talks between auxin, a regulator of plant development, and Ca2+, a universal second messenger, have been proposed to modulate developmental plasticity in plants. However, the underlying molecular mechanisms are largely unknown. Here, we report that in Arabidopsis roots, auxin elicits specific Ca2+ signaling patterns that spatially coincide with the expression pattern of auxin-regulated genes. We have identified the single EF-hand Ca2+-binding protein Ca2+-dependent modulator of ICR1 (CMI1) as an interactor of the Rho of plants (ROP) effector interactor of constitutively active ROP (ICR1). CMI1 expression is directly up-regulated by auxin, whereas the loss of function of CMI1 associates with the repression of auxin-induced Ca2+ increases in the lateral root cap and vasculature, indicating that CMI1 represses early auxin responses. In agreement, cmi1 mutants display an increased auxin response including shorter primary roots, longer root hairs, longer hypocotyls, and altered lateral root formation. Binding to ICR1 affects subcellular localization of CMI1 and its function. The interaction between CMI1 and ICR1 is Ca2+-dependent and involves a conserved hydrophobic pocket in CMI1 and calmodulin binding-like domain in ICR1. Remarkably, CMI1 is monomeric in solution and in vitro changes its secondary structure at cellular resting Ca2+ concentrations ranging between 10−9 and 10−8 M. Hence, CMI1 is a Ca2+-dependent transducer of auxin-regulated gene expression, which can function in a cell-specific fashion at steady-state as well as at elevated cellular Ca2+ levels to regulate auxin responses.

Combined use of calcium nitrate addition and anion exchange resin capping to control sedimentary phosphorus release and its nitrate‑nitrogen releasing risk

Calcium nitrate (Ca(NO3)2) addition can be used to control the release of phosphorus from sediments, however it can also cause an increase in the concentration of nitrate‑nitrogen (NO3−-N) in the water column. The risk of NO3−-N release from the Ca(NO3)2-injected sediments may be reduced by the placement of the anion exchange resin (AER) capping layer. In this study, the effectiveness of the combined use of Ca(NO3)2 addition and AER capping to prevent the liberation of phosphorus from sediments was investigated, and the reduction of the risk of NO3−-N released from the Ca(NO3)2-injected sediment by the AER capping was also evaluated. The combined application of Ca(NO3)2 addition and AER capping could tremendously reduce the amount of soluble reactive phosphorus (SR-P) in the overlying water, with SR-P reduction rates of 75.9–98.7%. Furthermore, it could cut down the contents of high-resolution diffusive gradients in thin films (DGT)-labile phosphorus in the sediments, resulting in the formation of phosphorus static layer in the upper sediments. The combined treatment using Ca(NO3)2 and AER had a relatively small effect on the contents of mobile phosphorus in the sediments, but it could greatly increase the amount of residual phosphorus in the top 30mm sediments (increased by 27.7–42.9%). The amount of NO3−-N in the overlying water under the action of the combined treatment method using Ca(NO3)2 and AER was much lower than that under the action of the single Ca(NO3)2 treatment during the early stage of sediment remediation. In conclusion, the combined use of Ca(NO3)2 addition and AER capping is a more promising strategy for the control of sedimentary phosphorus release than the single use of Ca(NO3)2 addition from the point of view of both the control efficiency of P release from sediments and the releasing risk of the added nitrate.

Molecular beam epitaxy of electron-doped infinite-layer Ca1−xRxCuO2 thin films

Infinite-layer CaCuO${}_{2}$ is an isolated essential block of high-temperature superconducting cuprates while superconductivity in this phase remains elusive. Using molecular beam epitaxy equipped with an atomic oxygen source, the authors present the growth of single crystalline electron-doped infinite-layer Ca${}_{1\ensuremath{-}x}{R}_{x}$CuO${}_{2}$ ($R$ = La${}^{3+}$, Nd${}^{3+}$, and Ce${}^{4+}$) thin films. The $R$ substitution significantly enhances the coherent crystal volume and the electronic conductivity. Traces of superconductivity are observed for the Nd substitution of 0.06. Microscopic defects limit the electronic transport of the CuO${}_{2}$ planes, thus the suppression of superconductivity.

Influence of Ca adsorption on the heterogeneous nucleation of α-Mg on Al4C3 particles: First-principles calculation and experiment

Abstract The addition of Ca in magnesium melt has a significant influence on the heterogeneous nucleation effect of Al4C3 particles with open question for the mechanism. We have conducted first-principles calculations of the adsorption of Ca and Mg atoms on Al4C3 surfaces to study the initial nucleation and growth of Mg atoms on Al4C3 surfaces. The single Ca or Mg adsorption, as well as Ca Mg co-adsorption on a 28-layer slab (A-type) of Al-terminated Al4C3(0001) surface has been simulated. We demonstrate that both Ca and Mg atoms tend to stabilize at the H2 site of Al-terminated Al4C3(0001) surface. Meanwhile, a comparative experiment is conducted to study the influence of Ca on the grain refining effect, showing that Ca atoms promotes the adsorption and nucleation growth of Mg atoms on Al4C3 surfaces.

Ultrashort nanosecond electric pulses evoke heterogeneous patterns of Ca2+ release from the endoplasmic reticulum of adrenal chromaffin cells

• 5 ns pulses cause diverse patterns of Ca 2+ release from the ER of chromaffin cells. • Patterns include a single Ca 2+ transient or multiple Ca 2+ spikes. • IP 3 - and caffeine-sensitive ER Ca 2+ stores are differentially involved. • Ca 2+ release due to membrane poration occurs from caffeine-sensitive stores. • Ca 2+ spikes are associated with Ca 2+ release mediated by IP 3 receptors.

Dual-FRET imaging of IP3 and Ca2+ revealed Ca2+-induced IP3 production maintains long lasting Ca2+ oscillations in fertilized mouse eggs

In most species, fertilization induces Ca2+ transients in the egg. In mammals, the Ca2+ rises are triggered by phospholipase Cζ (PLCζ) released from the sperm; IP3 generated by PLCζ induces Ca2+ release from the intracellular Ca2+ store through IP3 receptor, termed IP3-induced Ca2+ release. Here, we developed new fluorescent IP3 sensors (IRIS-2s) with the wider dynamic range and higher sensitivity (Kd = 0.047–1.7 μM) than that we developed previously. IRIS-2s employed green fluorescent protein and Halo-protein conjugated with the tetramethylrhodamine ligand as fluorescence resonance energy transfer (FRET) donor and acceptor, respectively. For simultaneous imaging of Ca2+ and IP3, using IRIS-2s as the IP3 sensor, we developed a new single fluorophore Ca2+ sensor protein, DYC3.60. With IRIS-2s and DYC3.60, we found that, right after fertilization, IP3 concentration ([IP3]) starts to increase before the onset of the first Ca2+ wave. [IP3] stayed at the elevated level with small peaks followed after Ca2+ spikes through Ca2+ oscillations. We detected delays in the peak of [IP3] compared to the peak of each Ca2+ spike, suggesting that Ca2+-induced regenerative IP3 production through PLC produces small [IP3] rises to maintain [IP3] over the basal level, which results in long lasting Ca2+ oscillations in fertilized eggs.

Correction: Towards a Better Detection of Horizontally Transferred Genes by Combining Unusual Properties Effectively

[This corrects the article DOI: 10.1371/journal.pone.0043126.].

Analysis of ATP-Induced Ca2+ Responses at Single Cell Level in Retinal Pigment Epithelium Monolayers.

Calcium is one of the most important second messengers in cells and thus involved in a variety of physiological processes. In retinal pigment epithelium (RPE), Ca2+ and its ATP-dependent signaling pathways play important roles in the retina maintenance functions. Changes in intracellular Ca2+ concentration can be measured from living cells by Ca2+ imaging. Combining these measurements with quantitative analysis of Ca2+ response properties enables studies of signaling pathways affecting RPE functions. However, robust tools for response analysis from large cell populations are lacking. We developed MATLAB-based analysis tools for single cell level Ca2+ response data recorded from large fields of intact RPE monolayers. The analysis revealed significant heterogeneity in ATP-induced Ca2+ responses inside cell populations regarding magnitude and response kinetics. Further analysis including response grouping and parameter correlations allowed us to characterize the populations at the level of single cells.

Isoflurane Inhibits Dopaminergic Synaptic Vesicle Exocytosis Coupled to CaV2.1 and CaV2.2 in Rat Midbrain Neurons

Volatile anesthetics affect neuronal signaling by poorly understood mechanisms. Activation of central dopaminergic pathways has been implicated in emergence from general anesthesia. The volatile anesthetic isoflurane differentially inhibits glutamatergic and GABAergic synaptic vesicle (SV) exocytosis by reducing presynaptic Ca2+ influx without affecting the Ca2+-exocytosis relationship, but its effects on dopaminergic exocytosis are unclear. We tested the hypothesis that isoflurane inhibits exocytosis in dopaminergic neurons. We used electrical stimulation or depolarization by elevated extracellular KCl to evoke exocytosis measured by quantitative live-cell fluorescence imaging in cultured rat ventral tegmental area neurons. Using trains of electrically evoked action potentials (APs), isoflurane inhibited exocytosis in dopaminergic neurons to a greater extent (30 ± 4% inhibition; p < 0.0001) than in non-dopaminergic neurons (15 ± 5% inhibition; p = 0.014). Isoflurane also inhibited exocytosis evoked by elevated KCl in dopaminergic neurons (35 ± 6% inhibition; p = 0.0007), but not in non-dopaminergic neurons (2 ± 4% inhibition). Pharmacological isolation of presynaptic Ca2+ channel subtypes showed that isoflurane inhibited KCl-evoked exocytosis mediated exclusively by either CaV2.1 (P/Q-type Ca2+ channels; 30 ± 5% inhibition; p = 0.0002) or by CaV2.2 (N-type Ca2+ channels; 35 ± 11% inhibition; p = 0.015). Additionally, isoflurane inhibited single AP-evoked Ca2+ influx by 41 ± 3% and single AP-evoked exocytosis by 34 ± 6%. Comparable reductions in exocytosis and Ca2+ influx were produced by lowering extracellular [Ca2+]. Thus, isoflurane inhibits exocytosis from dopaminergic neurons by a mechanism distinct from that in non-dopaminergic neurons involving reduced Ca2+ entry through CaV2.1 and/or CaV2.2.

Waveguiding in All-Garnet Heteroepitaxial Magneto-Optical Photonic Crystals

We report the properties of 1D all-garnet heteroepitaxial 21 layered magneto-optical photonic crystal designed and fabricated for the resonance wavelength 750 ± 3 nm. It is composed of alternating magnetooptical-active Bi3Fe5O12 and transparent Sm3Ga5O12 quarter-wavelength layers radio frequency magnetron sputtered onto single crystalline Ca, Mg, Zr:Gd3Ga5O12(111) substrate. Edges of the band gap and resonant central peaks in transmission and Faraday rotation spectra experience significant (about 60 nm) “blueshift” when the angle of light incidence increases up to 70°. Lower reflectance and strong enhancement of Faraday rotation of TE mode compared to the TM-polarized light testify a waveguiding of TE-mode within a resonant λ/2 Bi3Fe5O12 cavity.

Research on multi-camera calibration and point cloud correction method based on three-dimensional calibration object

The single camera measurement system can't obtain all the surface information of the object limited by the field of view, thus it can't achieve complete measurement of the object. Multi-camera system can overcome this difficulty. But it is difficult to unify the coordinate system of distinct cameras. In order to solve this problem, a global calibration method of multi-camera system is proposed. A three-dimensional cube calibration object is designed. Every camera is only calibrated on one surface of the cube calibration object. Because different surfaces of the cube calibration object are in a unified world coordinate, the coordinates of the feature points on different surfaces are naturally in the unified world coordinate system. Thus global calibration can be completed by calibrating multiple cameras at the same time. In addition, to minimize the error of calibration, a correction method is proposed. The correction parameters are obtained by the deviation between the world coordinates and the reconstructed coordinates of the feature points on calibration object. The parameters are applied to the measurement to improve the accuracy of the whole point cloud. Experiments are carried out on a multi-camera measurement system, and the results show that the method proposed in this paper is effective and feasible.

Taxicab Geometry Based Analysis on Skyline for Business Intelligence

This article describes how multi-criteria decision making problems are difficult to handle in normal SQL query processing. Skyline computation is generally used to solve these types of requirements by using dominance analysis and finding shortest distance with respect to a prime interesting point. However, in real life scenarios shortest distance may not be applicable in most of the cases due to different obstacles or barriers exist between the point of interests or places. In order to consider the presence of obstacles for geographically dispersed data, this research work uses Taxicab geometry for distance calculation, which is a simple Non-Euclidian geometry with minimum time complexity. Another limitation of previous skyline based works are that they only focus upon a single interesting point and can't be apply for multiple interesting points. This research article focuses upon multiple visiting points for the travelers in an optimized way. In addition to this, the article also selects areas for setting up of new business properties considering the constraints.

Structural basis for relief of phospholamban-mediated inhibition of the sarcoplasmic reticulum Ca2+-ATPase at saturating Ca2+ conditions

Sarcoplasmic reticulum Ca2+-ATPase (SERCA) is critical for cardiac Ca2+ transport. Reversal of phospholamban (PLB)-mediated SERCA inhibition by saturating Ca2+ conditions operates as a physiological rheostat to reactivate SERCA function in the absence of PLB phosphorylation. Here, we performed extensive atomistic molecular dynamics simulations to probe the structural mechanism of this process. Simulation of the inhibitory complex at superphysiological Ca2+ concentrations ([Ca2+] = 10 mm) revealed that Ca2+ ions interact primarily with SERCA and the lipid headgroups, but not with PLB's cytosolic domain or the cytosolic side of the SERCA-PLB interface. At this [Ca2+], a single Ca2+ ion was translocated from the cytosol to the transmembrane transport sites. We used this Ca2+-bound complex as an initial structure to simulate the effects of saturating Ca2+ at physiological conditions ([Ca2+]total ≈ 400 μm). At these conditions, ∼30% of the Ca2+-bound complexes exhibited structural features consistent with an inhibited state. However, in ∼70% of the Ca2+-bound complexes, Ca2+ moved to transport site I, recruited Glu771 and Asp800, and disrupted key inhibitory contacts involving the conserved PLB residue Asn34 Structural analysis showed that Ca2+ induces only local changes in interresidue inhibitory interactions, but does not induce repositioning or changes in PLB structural dynamics. Upon relief of SERCA inhibition, Ca2+ binding produced a site I configuration sufficient for subsequent SERCA activation. We propose that at saturating [Ca2+] and in the absence of PLB phosphorylation, binding of a single Ca2+ ion in the transport sites rapidly shifts the equilibrium toward a noninhibited SERCA-PLB complex.

Research of Image Retrieval Method Based on Improved Feature

In the process of image retrieval, the traditional single feature can't reflect the distribution and details of image color and content, which have some adverse influence on the performance of image retrieval. This paper presents an image retrieval method based on improved color and texture feature. According to the mean of the HSV color model region, algorithm obtains the mean eigenvectors of the color feature by using the improved correlation weight model. The image decomposition transformation is obtained through the Haar wavelet. In the low-frequency component of the image decomposition, the low-frequency texture feature vector is obtained according to the low-frequency feature structure model. The similarity of image is calculated by the Canberra distance. Experimental results show that:the methods of retrieval are tested in Corel-1000 and Corel-5000 standard gallery, which accuracy rate and retrieval rate have been improved accordingly.

Specificity in the interaction of high-voltage-activated Ca2+ channel types with Ca2+-dependent afterhyperpolarizations in magnocellular supraoptic neurons.

Magnocellular oxytocin (OT) and vasopressin (VP) neurons express an afterhyperpolarization (AHP) following spike trains that attenuates firing rate and contributes to burst patterning. This AHP includes contributions from an apamin-sensitive, medium-duration AHP (mAHP) and from an apamin-insensitive, slow-duration AHP (sAHP). These AHPs are Ca2+ dependent and activated by Ca2+ influx through voltage-gated Ca2+ channels. Across central nervous system neurons that generate Ca2+-dependent AHPs, the Ca2+ channels that couple to the mAHP and sAHP differ greatly, but for magnocellular neurosecretory cells this relationship is unknown. Using simultaneous whole cell recording and Ca2+ imaging, we evaluated the effect of specific high-voltage-activated (HVA) Ca2+ channel blockers on the mAHP and sAHP. Block of all HVA channels via 400 μM Cd2+ inhibited almost the entire AHP. We tested nifedipine, conotoxin GVIA, agatoxin IVA, and SNX-482, specific blockers of L-, N-, P/Q-, and R-type channels, respectively. The N-type channel blocker conotoxin GVIA (1 μM) was the only toxin that inhibited the mAHP in either OT or VP neurons although the effect on VP neurons was weaker by comparison. The sAHP was significantly inhibited by N-type block in OT neurons and by R-type block in VP neurons although neither accounted for the entirety of the sAHP. Thus the mAHP appears to be elicited by Ca2+ from mostly N-type channels in both OT and VP neurons, but the contributions of specific Ca2+ channel types to the sAHP in each cell type are different. Alternative sources to HVA channels may contribute Ca2+ for the sAHP. NEW & NOTEWORTHY Despite the importance of afterhyperpolarization (AHP) mechanisms for regulating firing behavior of oxytocin (OT) and vasopressin (VP) neurons of supraoptic nucleus, which types of high-voltage-activated Ca2+ channels elicit AHPs in these cells was unknown. We found that N-type channels couple to the medium AHP in both cell types. For the slow AHP, N-type channels contribute in OT neurons, whereas R-type contribute in VP neurons. No single Ca2+ channel blocker abolished the entire AHP, suggesting that additional Ca2+ sources are involved.

Heading multi-mode control based on soft-switching for autonomous underwater vehicle

This paper aims to solve the problem that a single control method can't fit to each operating condition of heading control for autonomous underwater vehicle (AUV). A multi-mode strategy based on soft-switching is proposed, which can get better performance by smooth switching of control modes. The control mode consists of two levels, which is named as two-level-mode method. On the first level, the control mode is divided into six according to the operating state of AUV. On the second level, based on the existing mode the control mode is divided into three depending on AUV′ speed. In addition, the BB-PID controller is designed for heading control, as well as the sigmoid function is constructed to smoothly switching at different speed without saltation. The simulation and experiment results demonstrate that BB-PID controller achieves outstanding performance and the switching strategy is much more effective by comparing the RMS, RMSE, SSE between switching based on sigmoid function and switching based on threshold.

Molecular Characterization of an SV Capture Site in the Mid-Region of the Presynaptic CaV2.1 Calcium Channel C-Terminal.

Neurotransmitter is released from presynaptic nerve terminals at fast-transmitting synapses by the action potential-gating of voltage dependent calcium channels (CaV), primarily of the CaV2.1 and CaV2.2 types. Entering Ca2+ diffuses to a nearby calcium sensor associated with a docked synaptic vesicle (SV) and initiates its fusion and discharge. Our previous findings that single CaVs can gate SV fusion argued for one or more tethers linking CaVs to docked SVs but the molecular nature of these tethers have not been established. We recently developed a cell-free, in vitro biochemical assay, termed SV pull-down (SV-PD), to test for SV binding proteins and used this to demonstrate that CaV2.2 or the distal third of its C-terminal can capture SVs. In subsequent reports we identified the binding site and characterized an SV binding motif. In this study, we set out to test if a similar SV-binding mechanism exists in the primary presynaptic channel type, CaV2.1. We cloned the chick variant of this channel and to our surprise found that it lacked the terminal third of the C-terminal, ruling out direct correlation with CaV2.2. We used SV-PD to identify an SV binding site in the distal half of the CaV2.1 C-terminal, a region that corresponds to the central third of the CaV2.2 C-terminal. Mutant fusion proteins combined with motif-blocking peptide strategies identified two domains that could account for SV binding; one in an alternatively spliced region (E44) and a second more distal site. Our findings provide a molecular basis for CaV2.1 SV binding that can account for recent evidence of C-terminal-dependent transmitter release modulation and that may contribute to SV tethering within the CaV2.1 single channel Ca2+ domain.

HYBRID GEOMETRIC CALIBRATION METHOD FOR MULTI-PLATFORM SPACEBORNE SAR IMAGE WITH SPARSE GCPS

Abstract. Geometric calibration is able to provide high-accuracy geometric coordinates of spaceborne SAR image through accurate geometric parameters in the Range-Doppler model by ground control points (GCPs). However, it is very difficult to obtain GCPs that covering large-scale areas, especially in the mountainous regions. In addition, the traditional calibration method is only used for single platform SAR images and can’t support the hybrid geometric calibration for multi-platform images. To solve the above problems, a hybrid geometric calibration method for multi-platform spaceborne SAR images with sparse GCPs is proposed in this paper. First, we calibrate the master image that contains GCPs. Secondly, the point tracking algorithm is used to obtain the tie points (TPs) between the master and slave images. Finally, we calibrate the slave images using TPs as the GCPs. We take the Beijing-Tianjin- Hebei region as an example to study SAR image hybrid geometric calibration method using 3 TerraSAR-X images, 3 TanDEM-X images and 5 GF-3 images covering more than 235 kilometers in the north-south direction. Geometric calibration of all images is completed using only 5 GCPs. The GPS data extracted from GNSS receiver are used to assess the plane accuracy after calibration. The results after geometric calibration with sparse GCPs show that the geometric positioning accuracy is 3 m for TSX/TDX images and 7.5 m for GF-3 images.