Temporal progress model of metabolic syndrome for clinical decision support system

The development of an integrated and personalized healthcare system is becoming an important issue in the modern healthcare industry. One of main objectives of integrated healthcare system is to effectively manage patients having chronic diseases that require long term care and its temporal information plays an important role to manage the statuses of diseases. Thus, a patient having chronic disease needs to visit the hospital periodically, which generates large volume of medical examination data. Among the various chronic diseases, metabolic syndrome (MS) has become a popular chronic disease in many countries. There have been efforts to develop an MS risk quantification and prediction model and to integrate it into personalized healthcare system, so as to predict the risk of having MS in the future. However, the development of methods for temporal progress management of metabolic syndrome has not been widely investigated. This paper proposes a method for identifying the temporal progress of MS patients' status based on the chronological clustering methodology. To investigate the temporal changes of disease status, we develop a chronological distance variance model that quantifies the difference of areal similarity degree (ASD) values between estimated and examined results of MS risk factors. We evaluate the clinical effectiveness of the temporal progress model by using sample subjects' examination results that have been measured for 10 years. We further elaborate the accuracy of the proposed temporal progress estimation method by using multiple linear regression method. Then, we develop a tier-based patients' MS status classification based on the chronological distance variance. The tier classification is based on the sensitivity for temporal change of MS status according to different values of control range of chronological distance variance. Our proposed temporal change identification method and patients' tier classification are expected to be incorporated with the integrated healthcare systems to help physicians with identifying the temporal progress of MS patients' health status and MS patients with self-management at home environments.     

On the relationship between a resource based measure of geodiversity and broad scale biodiversity patterns

Geodiversity, (diversity of the geosphere) incorporates many of the environmental patterns and processes that are considered drivers of biodiversity. Components of geodiversity (climate, topography, geology and hydrology) can be considered in terms of their resource giving potential, where resources are taken as energy, water, space and nutrients. The total amount of these resources, along with their spatial and temporal variation, is herein proposed as a compound index of geodiversity that has the potential to model broad scale biodiversity patterns. This paper outlines potential datasets that could be used to represent geodiversity, and then reviews the theoretical links between each element of the proposed compound index of geodiversity (overall resource availability, temporal variation and spatial variation in those resources) and broad-scale patterns of biodiversity. Support for the influence of each of the elements of geodiversity on overall biodiversity patterns was found in the literature, although the majority of relevant research focuses on resource availability, particularly available energy. The links between temporal and spatial variation in resources and biodiversity have been less thoroughly investigated in the literature. For the most part, it was reported that overall resource availability, temporal variation and spatial variation in those resources do not act in isolation in terms of controlling biodiversity. Overall there are sufficient datasets to calculate the proposed compound index of geodiversity, and evidence in the literature for links between the geographical distribution of biodiversity and each of the elements of the compound index defined. Since data for measuring geodiversity is more spatially consistent and widely available (thanks to satellite remote sensing) geodiversity has potential as a conservation planning tool, especially where biological data are not available or sparsely distributed.     

Comparative analysis of the regulation of vertical posture in athletes of different sports qualifications

The goal of study was to investigate the regulation of balance in athletes with different sports qualifications: masters of sport (MS, n=18) and candidates for master of sports (CMS, n=13). Balance examined by means of stabilographic complex ("Rhythm". Russia) in the static tests: in simple bipedal stance (BS) and squat positions (SQ), as well as in the dynamic tests: "Involute", evaluating the tracking movement and "Step input", assessing the reaction of the whole body on the visual-motor task. It was found that the MS with the same anthropometric data, PWC 170 and trunk power did not differ in linear and angular velocity of oscillations of the center of pressure (CP) in BS and SQ positions. MS had a relative dominance of low-frequency oscillations in the spectral analysis in the BS test with eyes open. In the test "Step input" MS had a lower latent period of reaction, a greater speed and an accuracy of the body motion forward and back in response to the step input signals, while they had a relative dominance of high frequency oscillations. Thus, the results showed that the masters of sport have improved postural regulation, which manifested itself mainly in the dynamic test on the speed and accuracy of the vertical body reaction to input visual signals.     

Systematic tuning of parameters in support vector clustering

Clustering algorithms divide a set of observations into groups so that members of the same group share common features. In most of the algorithms, tunable parameters are set arbitrarily or by trial and error, resulting in less than optimal clustering. This paper presents a global optimization strategy for the systematic and optimal selection of parameter values associated with a clustering method. In the process, a performance criterion for the optimization model is proposed and benchmarked against popular performance criteria from the literature (namely, the Silhouette coefficient, Dunn's index, and Davies-Bouldin index). The tuning strategy is illustrated using the support vector clustering (SVC) algorithm and simulated annealing. In order to reduce the computational burden, the paper also proposes an alternative to the adjacency matrix method (used for the assignment of cluster labels), namely the contour plotting approach. Datasets tested include the iris and the thyroid datasets from the UCI repository, as well as lymphoma and breast cancer data. The optimal tuning parameters are determined efficiently, while the contour plotting approach leads to significant reductions in computational effort (CPU time) especially for large datasets. The performance criteria comparisons indicate mixed results. Specifically, the Silhouette coefficient and the Davies-Bouldin index perform better, while the Dunn's index is worse on average than the proposed performance index.     

Studies of the Ndh complex and photosystem II from mesophyll and bundle sheath chloroplasts of the C4-type plant Zea mays

In C(4) plants, granal mesophyll (MS) chloroplasts contain higher photosystem (PS) II and lower PS I activity than agranal bundle sheath (BS) chloroplasts. The maize NAD(P)H dehydrogenase or NAD(P)H-plastoquinone oxidoreductase (also named Ndh complex) from MS and BS chloroplasts, contains at least 11 subunits (NdhA-K) and is homologous to NADH dehydrogenase or Complex I from mitochondria and bacteria. The amount of Ndh complex is higher in BS compared with MS chloroplasts. However, there is little information about the interdependence of the PS II and Ndh complex in chlororespiration and linear and cyclic electron transport in C(4) plants. To characterize the expression of the PS II and Ndh complex in maize plastids, we used cytochrome b559 (cyt b559) antibodies and Ndh immunoglobulins (IgG) to analyze the Ndh complex and PS II in both MS and BS chloroplasts from maize leaves by Western blotting and immunolabeling. In Western blot experiments, it was found that the amount of cyt b559 (a marker for PS II) is 7-8 times higher in MS than BS chloroplasts. Conversely, the NdhH, -J, -K and -E content is 2.5-3 times higher in BS than MS chloroplasts. Similar results were obtained in immunolabeling experiments using Ndh IgGs and cyt b559 antibodies in MS and BS chloroplasts. These data suggest that in BS chloroplasts, ATP could be produced mainly by cyclic electron transport around PS I and Ndh complexes. Conversely, the linear electron transport in BS chloroplasts via PS II could have a lower production of ATP. These results also suggest that the contribution of the Ndh complex in the production of ATP in MS chloroplasts is minimal and that instead, this complex could have a chlororespiratory role.     

Methods for investigating biosurfactants and bioemulsifiers: a review

Microorganisms produce biosurfactant (BS)/bioemulsifier (BE) with wide structural and functional diversity which consequently results in the adoption of different techniques to investigate these diverse amphiphilic molecules. This review aims to compile information on different microbial screening methods, surface active products extraction procedures, and analytical terminologies used in this field. Different methods for screening microbial culture broth or cell biomass for surface active compounds production are also presented and their possible advantages and disadvantages highlighted. In addition, the most common methods for purification, detection, and structure determination for a wide range of BS and BE are introduced. Simple techniques such as precipitation using acetone, ammonium sulphate, solvent extraction, ultrafiltration, ion exchange, dialysis, ultrafiltration, lyophilization, isoelectric focusing (IEF), and thin layer chromatography (TLC) are described. Other more elaborate techniques including high pressure liquid chromatography (HPLC), infra red (IR), gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance (NMR), and fast atom bombardment mass spectroscopy (FAB-MS), protein digestion and amino acid sequencing are also elucidated. Various experimental strategies including static light scattering and hydrodynamic characterization for micelles have been discussed. A combination of various analytical methods are often essential in this area of research and a numbers of trials and errors to isolate, purify and characterize various surface active agents are required. This review introduces the various methodologies that are indispensable for studying biosurfactants and bioemulsifiers.     

落叶阔叶林反照率的时间变化与影响因素

反照率原位测量对生态系统能量收支及其遥感应用至关重要,但目前坡面地形反照率的测量方式有局限且可见光与近红外波段反照率时间变化的差异尚不清楚。本研究以东北地区帽儿山森林生态站的落叶阔叶林为例,探究入射和反射太阳辐射(SR,300～2800 nm)、光合有效辐射(PAR,400～700 nm)、近红外辐射(NIR,700～2800 nm)的反照率时间变化特征及其影响因子,同时分析了两种辐射表安装方式反照率的差异。结果表明: 晴天SR和NIR反照率日变化呈上下午不对称的U型曲线,但PAR从早到晚递增;阴天反照率均先急剧下降后趋于稳定。平行于坡面测量增大了反照率的日均值,但缓和了SR、NIR反照率日不对称的现象。从整个生长季来看,SR、NIR与PAR反照率水平测量时最大值分别为0.16、0.27和0.11,最小值分别为0.07、0.11和0.03。SR和NIR反照率季节变化均为先增大后减小(7月为峰值),PAR则相反,SR反照率主要受NIR而不是PAR控制。各波段反照率季节变化的影响因子按照贡献率排序为宽带归一化植被指数(61.7%～78.5%,可表征叶面积指数)>太阳高度角(15.4%～36.9%)>晴空指数(0.4%～36.9%)。     

Kinetics of the actions of caffeine and procaine on the Ca2+-gated cation channel in sarcoplasmic reticulum vesicles

The effects of caffeine and procaine on the Ca2+-gated cation channel in sarcoplasmic reticulum (SR) vesicles were studied by measuring choline influx. The choline influx in SR vesicles was measured by following the change in light scattering intensity using a stopped flow apparatus. From the kinetic analysis of the rate of choline influx, the following results were obtained. (1) The rate of choline influx was enhanced when Ca2+ bound to the Ca2+-receptor site of the Ca2+-gated cation channel. (2) Caffeine enhanced the choline influx by increasing only the affinity of Ca2+ for the receptor site of the channel and thus regulated the equilibrium between open and closed states of the channel. The affinity increased about 14-fold upon caffeine binding. The dissociation constant of caffeine was 10 mM. (3) In contrast, procaine itself blocked the choline influx mediated by the Ca2+-gated cation channel. The blockade followed a single-site titration curve with a Ca2+-dependent dissociation constant of 0.44 mM at 2 x 10(-6) M Ca2+. The Ca2+-dependence was explained by assuming that procaine would bind to the inhibitory site only when the channel was open. (4) Procaine also inhibited the choline influx enhanced by caffeine. The blockade could be explained on the basis of the above kinetic model.     

Impaired calcium release during fatigue.

Impaired calcium release from the sarcoplasmic reticulum (SR) has been identified as a contributor to fatigue in isolated skeletal muscle fibers. The functional importance of this phenomenon can be quantified by the use of agents, such as caffeine, which can increase SR Ca(2+) release during fatigue. A number of possible mechanisms for impaired calcium release have been proposed. These include reduction in the amplitude of the action potential, potentially caused by extracellular K(+) accumulation, which may reduce voltage sensor activation but is counteracted by a number of mechanisms in intact animals. Reduced effectiveness of SR Ca(2+) channel opening is caused by the fall in intracellular ATP and the rise in Mg(2+) concentrations that occur during fatigue. Reduced Ca(2+) available for release within the SR can occur if inorganic phosphate enters the SR and precipitates with Ca(2+). Further progress requires the development of methods that can identify impaired SR Ca(2+) release in intact, blood-perfused muscles and that can distinguish between the various mechanisms proposed.     

Protein and peptide identification algorithms using MS for use in high-throughput, automated pipelines

Current proteomics experiments can generate vast quantities of data very quickly, but this has not been matched by data analysis capabilities. Although there have been a number of recent reviews covering various aspects of peptide and protein identification methods using MS, comparisons of which methods are either the most appropriate for, or the most effective at, their proposed tasks are not readily available. As the need for high-throughput, automated peptide and protein identification systems increases, the creators of such pipelines need to be able to choose algorithms that are going to perform well both in terms of accuracy and computational efficiency. This article therefore provides a review of the currently available core algorithms for PMF, database searching using MS/MS, sequence tag searches and de novo sequencing. We also assess the relative performances of a number of these algorithms. As there is limited reporting of such information in the literature, we conclude that there is a need for the adoption of a system of standardised reporting on the performance of new peptide and protein identification algorithms, based upon freely available datasets. We go on to present our initial suggestions for the format and content of these datasets.     

Microbiological decomposition of organic matter in the bottom sediments of Lithuanian lakes

The rates of the processes of bacterial sulfate reduction (SR) and decomposition of organic matter (D(total)) were studied in the bottom sediments (BS) of 14 lakes in Lithuanian national and regional parks in the summers of 1998-2002. Anaerobic processes accounted for an average of 92% of D(total) in the depressions of deep-water lakes; for the sediments of shallow lakes, high rates of oxygen uptake were noted. The SR rate in different lakes varied from 0.09 to 2.60 mg S(2-)/(dm3 day). At low sulfate concentrations (13.3-70.6 mg S-SO4(2-) /dm3), characteristic of the BS of freshwater ecosystems, the main factor that affected the SR rate in the BS of the lakes studied was the content of readily available organic matter, only in special cases, was it affected by a change in the sulfate ion concentration. In shallow lakes, both temperature-dependent activation of sulfate-reducing bacteria and their inhibition by acidification of the environment were recorded. The contribution of SR to D(total) was 0.2 to 11.0%.     

Dynamic graph convolution neural network based on spatial-temporal correlation for air quality prediction

Air pollution is a serious threat to both the ecological environment and the physical health of individuals. Therefore, accurate air quality prediction is urgent and necessary for pollution mitigation and residents’ travel. However, few existing models are established based on the dynamic spatiotemporal correlation of air pollutants to predict air quality. In this paper, a novel deep learning model combining the dynamic graph convolutional network and the multi-channel temporal convolutional network (DGC-MTCN) is proposed for air quality prediction. To efficiently represent the time-varying spatial dependencies, a new spatiotemporal dynamic correlation calculation method based on gray relation analysis is proposed to construct dynamic adjacency matrices. Then, the spatiotemporal features are sufficiently extracted by the graph convolutional network and the multi-channel temporal convolutional network. Two real-world air quality datasets collected from Beijing and Fushun are applied to verify the performance of our proposed model. The experimental results show that compared with other baselines, the DGC-MTCN model has excellent prediction accuracy. Especially for the prediction of multi-step and different stations, our model performs better temporal stability and generalization ability.     

Blockade of cardiac sarcoplasmic reticulum K+ channel by Ca2+: two-binding-site model of blockade.

Potassium countercurrent through the SR K+ channel plays an important role in Ca2+ release from the SR. To see if Ca2+ regulates the channel, we incorporated canine cardiac SR K+ channel into lipid bilayers. Calcium ions present in either the SR lumenal (trans) or cytoplasmic (cis) side blocked the cardiac SR K+ channel in a voltage-dependent manner. When Ca2+ was present on both sides, however, the block appeared to be voltage independent. A two-binding site model of blockade by an impermeant divalent cation (Ca2+) can explain this apparent contradiction. Estimates of SR Ca2+ concentration suggest that under physiological conditions the cardiac SR K+ channel is partially blocked by Ca2+ ions present in the lumen of the SR. The reduction in lumenal [Ca2+] during Ca2+ release could increase K+ conductance.     

Differential scattering of circularly polarized light as a unique probe of polynucleosome superstructures

A theoretical approach to modeling Circular Intensity Differential Scattering (CIDS) of native chromatin as multiple scattering of dipoles is discussed without the Born approximation. The model can explain the experimental data in the literature. It is shown that CIDS contains more structural information than does total light scattering and to a good approximation is independent of the length of the scattering molecules. Finally, CIDS in conjunction with traditional light scattering measurements should aid in discriminating between various alternative models of higher order chromatin structure now being proposed. Generalization of this theoretical study to other complex biomolecular structures, is also briefly discussed.     

Theory of excitation-contraction coupling in cardiac muscle.

The consequences of cardiac excitation-contraction coupling by calcium-induced calcium release were studied theoretically, using a series of idealized models solved by analytic and numerical methods. "Common-pool" models, those in which the trigger calcium and released calcium pass through a common cytosolic pool, gave nearly all-or-none regenerative calcium releases (in disagreement with experiment), unless their loop gain was made sufficiently low that it provided little amplification of the calcium entering through the sarcolemma. In the linear (small trigger) limit, it was proven rigorously that no common-pool model can give graded high amplification unless it is operated on the verge of spontaneous oscillation. To circumvent this problem, we considered two types of "local-control" models. In the first type, the local calcium from a sarcolemmal L-type calcium channel directly stimulates a single, immediately opposed SR calcium release channel. This permits high amplification without regeneration, but requires high conductance of the SR channel. This problem is avoided in the second type of local control model, in which one L-type channel triggers a regenerative cluster of several SR channels. Statistical recruitment of clusters results in graded response with high amplification. In either type of local-control model, the voltage dependence of SR calcium release is not exactly the same as that of the macroscopic sarcolemmal calcium current, even though calcium is the only trigger for SR release. This results from the existence of correlations between the stochastic openings of individual sarcolemmal and SR channels. Propagation of regenerative calcium-release waves (under conditions of calcium overload) was analyzed using analytically soluble models in which SR calcium release was treated phenomenalogically. The range of wave velocities observed experimentally is easily explained; however, the observed degree of refractoriness to wave propagation requires either a strong dependence of SR calcium release on the rate of rise of cytosolic calcium or localization of SR release sites to one point in the sarcomere. We conclude that the macroscopic behavior of calcium-induced calcium release depends critically on the spatial relationships among sarcolemmal and SR calcium channels, as well as on their kinetics.     

Influence of total lipid concentration, bile salt:lecithin ratio, and cholesterol content on inter-mixed micellar/vesicular (non-lecithin-associated) bile salt concentrations in model bile.

We modified classic equilibrium dialysis methodology to correct for dialysant dilution and Donnan effects, and have systematically studied how variations in total lipid concentration, bile salt (taurocholate):lecithin (egg yolk) ratio, and cholesterol content influence inter-mixed micellar/vesicular (non-lecithin-associated) concentrations (IMC) of bile salts (BS) in model bile. To simulate large volumes of dialysant, the total volume (1 ml) of model bile was exchanged nine times during dialysis. When equilibrium was reached, dialysate BS concentrations plateaued, and initial and final BS concentrations in the dialysant were identical. After corrections for Donnan effects, IMC values were appreciably lower than final dialysate BS concentrations. Quasielastic light scattering was used to validate these IMC values by demonstrating that lipid particle sizes and mean scattered light intensities did not vary when model biles were diluted with aqueous BS solutions of the appropriate IMC. Micelles and vesicles were separated from cholesterol-supersaturated model bile, utilizing high performance gel chromatography with an eluant containing the IMC. Upon rechromatography of micelles and vesicles using an identical IMC, there was no net transfer of lipid between micelles and vesicles. To simulate dilution during gel filtration, model biles were diluted with 10 mM Na cholate, the prevailing literature eluant, resulting in net transfer of lipid between micelles and vesicles, the direction of which depended upon total lipid concentration and BS/lecithin ratio. Using the present methodology, we demonstrated that inter-mixed micellar/vesicular concentrations (IMC) values increased strongly (5 to 40 mM) with increases in both bile salt (BS):lecithin ratio and total lipid concentration, whereas variations in cholesterol content had no appreciable effects. For model biles with typical physiological biliary lipid compositions, IMC values exceeded the critical micellar concentration of the pure BS, implying that in cholesterol-supersaturated biles, simple BS micelles coexist with mixed BS/lecithin/cholesterol micelles and cholesterol/lecithin vesicles. We believe that this methodology allows the systematic evaluation of IMC values, with the ultimate aim of accurately separating micellar, vesicular, and potential other cholesterol-carrying particles from native bile.     

Novel biodegradable aliphatic poly(butylene succinate-co-cyclic carbonate)s with functional carbonate building blocks. 1. Chemical synthesis and their structural and physical characterization

This study presents chemical synthesis, structural, and physical characterization of novel biodegradable aliphatic poly(butylene succinate-co-cyclic carbonate)s P(BS-co-CC) bearing functional carbonate building blocks. First, five kinds of six-membered cyclic carbonate monomers, namely, trimethylene carbonate (TMC), 1-methyl-1,3-trimethylene carbonate (MTMC), 2,2-dimethyl-1,3-trimethylene carbonate (DMTMC), 5-benzyloxytrimethylene carbonate (BTMC), and 5-ethyl-5-benzyloxymethyl trimethylene carbonate (EBTMC), were well prepared from ethyl chloroformate and corresponding diols at 0 degrees C in THF solution with our modified synthetic strategies. Then, a series of new P(BS-co-CC)s were synthesized at 210 degrees C through a simple combination of poly-condensation and ring-opening-polymerization (ROP) of hydroxyl capped PBS macromers and the prepared carbonate monomers, and titanium tetra-isopropoxide Ti(i-OPr)4 was used as a more suitable catalyst of 5 candidate catalysts which could concurrently catalyze poly-condensation and ROP. By means of NMR, GPC, FTIR, and thermal analytical instruments, macromolecular structures and physical properties have been characterized for these aliphatic poly(ester carbonate)s. The experimental results indicated that novel biodegradable P(BS-co-CC)s were successfully synthesized with number average molecular weight Mn ranging from 24.3 to 99.6 KDa and various CC molar contents without any detectable decarboxylation and that the more bulky side group was attached to a cyclic carbonate monomer, the lower reactivity for its copolymerization would be observed. The occurrences of 13C NMR signal splitting of succinyl carbonyl attributed to the BS building blocks could be proposed due to the randomized sequences of BS and CC building blocks. FTIR characterization indicated two distinct absorption bands at 1716 and 1733 approximately 1735 cm(-1), respectively, stemming from carbonyl stretching modes for corresponding BS and CC units. With regard to their thermal properties, it is seen that the synthesized P(BS-co-CC)s exhibited thermal degradation temperatures 10 approximately 20 degrees C higher than that of PBS. On the basis of the synthesized P(BS-co-BTMC)s, new aliphatic poly(butylene succinate-co-5-hydroxy trimethylene carbonate)s were further synthesized, bearing hydrophilic hydroxyl pendant functional groups through an optimized Pd/C catalyzed hydrogenation. These semi-crystalline new biodegradable aliphatic copolymers with tunable physical properties and functional carbonate building blocks might be expected as potential new biomaterials.     

Encoding of acoustic directional information by saccular afferents of the sleeper goby, Dormitator latifrons

This paper reports on directional response properties of saccular afferents of the sleeper goby, Dormitator latifrons, to 100-Hz acoustic particle motions with a focus on testing the hypothesis that the response directionality of a fish's auditory afferents derives from the morphological polarity of sensory hair cells in the otolithic organs. Spontaneous rates (SR) and best sensitivities (BS) of saccular afferents ranged from 0 to 162 spikes/sec and from 0.2- to 100-nm RMS displacement. SR did not vary with BS. Most saccular afferents were phase-locked to sinusoidal stimulation and had sustained temporal response patterns with some adaptation. All saccular afferents were directionally sensitive to the stimulus, and the sharpness of directional response curves was determined by a directionality index (DI). The DI ranged from 0.64 to 1.50 (mean=1.02, SE=0.02, n=100) and gradually decreased with stimulus level throughout afferents' response dynamic range. Many afferents had approximately symmetric directional response curves relative to their best response axes (BRA). BRA of most afferents remained constant with stimulus level. The BRA distribution had a peak along an axis that correlates closely with the morphological polarity of saccular hair cells. Therefore, our results strongly support the hypothesis. Accepted: 19 December 1997     

Differential scattering of circularly polarized light as a unique probe of polynucleosome superstructures. A simulation by multiple scattering of dipoles

A theoretical approach to modeling Circular Intensity Differential Scattering (CIDS) of native chromatin as multiple scattering of dipoles is discussed without the Born approximation. The model can explain the experimental data in the literature. It is shown that CIDS contains more structural information than does total light scattering and to a good approximation is independent of the length of the scattering molecules. Finally, CIDS in conjunction with traditional light scattering measurements should aid in discriminating between various alternative models of higher order chromatin structure now being proposed. Generalization of this theoretical study to other complex biomolecular structures, is also briefly discussed.     

Sarcoplasmic Reticulum K+ (TRIC) Channel Does Not Carry Essential Countercurrent during Ca2+ Release

The charge translocation associated with sarcoplasmic reticulum (SR) Ca²⁺ efflux is compensated for by a simultaneous SR K⁺ influx. This influx is essential because, with no countercurrent, the SR membrane potential (V_m) would quickly (<1 ms) reach the Ca²⁺ equilibrium potential and SR Ca²⁺ release would cease. The SR K⁺ trimeric intracellular cation (TRIC) channel has been proposed to carry the essential countercurrent. However, the ryanodine receptor (RyR) itself also carries a substantial K⁺ countercurrent during release. To better define the physiological role of the SR K⁺ channel, we compared SR Ca²⁺ transport in saponin-permeabilized cardiomyocytes before and after limiting SR K⁺ channel function. Specifically, we reduced SR K⁺ channel conduction 35 and 88% by replacing cytosolic K⁺ for Na⁺ or Cs⁺ (respectively), changes that have little effect on RyR function. Calcium sparks, SR Ca²⁺ reloading, and caffeine-evoked Ca²⁺ release amplitude (and rate) were unaffected by these ionic changes. Our results show that countercurrent carried by SR K⁺ (TRIC) channels is not required to support SR Ca²⁺ release (or uptake). Because K⁺ enters the SR through RyRs during release, the SR K⁺ (TRIC) channel most likely is needed to restore trans-SR K⁺ balance after RyRs close, assuring SR V_m stays near 0 mV.