Ionic mechanisms and Ca2+ dynamics underlying the glucose response of pancreatic β cells: a simulation study

To clarify the mechanisms underlying the pancreatic β-cell response to varying glucose concentrations ([G]), electrophysiological findings were integrated into a mathematical cell model. The Ca2+ dynamics of the endoplasmic reticulum (ER) were also improved. The model was validated by demonstrating quiescent potential, burst–interburst electrical events accompanied by Ca2+ transients, and continuous firing of action potentials over [G] ranges of 0–6, 7–18, and >19 mM, respectively. These responses to glucose were completely reversible. The action potential, input impedance, and Ca2+ transients were in good agreement with experimental measurements. The ionic mechanisms underlying the burst–interburst rhythm were investigated by lead potential analysis, which quantified the contributions of individual current components. This analysis demonstrated that slow potential changes during the interburst period were attributable to modifications of ion channels or transporters by intracellular ions and/or metabolites to different degrees depending on [G]. The predominant role of adenosine triphosphate–sensitive K+ current in switching on and off the repetitive firing of action potentials at 8 mM [G] was taken over at a higher [G] by Ca2+- or Na+-dependent currents, which were generated by the plasma membrane Ca2+ pump, Na+/K+ pump, Na+/Ca2+ exchanger, and TRPM channel. Accumulation and release of Ca2+ by the ER also had a strong influence on the slow electrical rhythm. We conclude that the present mathematical model is useful for quantifying the role of individual functional components in the whole cell responses based on experimental findings

Gradient-based parameter optimization method to determine membrane ionic current composition in human induced pluripotent stem cell-derived cardiomyocytes

Premature cardiac myocytes derived from human induced pluripotent stem cells (hiPSC-CMs) show heterogeneous action potentials (APs), probably due to different expression patterns of membrane ionic currents. We developed a method for determining expression patterns of functional channels in terms of whole-cell ionic conductance (Gx) using individual spontaneous AP configurations. It has been suggested that apparently identical AP configurations can be obtained using different sets of ionic currents in mathematical models of cardiac membrane excitation. If so, the inverse problem of Gx estimation might not be solved. We computationally tested the feasibility of the gradient-based optimization method. For a realistic examination, conventional 'cell-specific models' were prepared by superimposing the model output of AP on each experimental AP recorded by conventional manual adjustment of Gxs of the baseline model. Gxs of 4–6 major ionic currents of the 'cell-specific models' were randomized within a range of ± 5–15% and used as an initial parameter set for the gradient-based automatic Gxs recovery by decreasing the mean square error (MSE) between the target and model output. Plotting all data points of the MSE–Gx relationship during optimization revealed progressive convergence of the randomized population of Gxs to the original value of the cell-specific model with decreasing MSE. The absence of any other local minimum in the global search space was confirmed by mapping the MSE by randomizing Gxs over a range of 0.1–10 times the control. No additional local minimum MSE was obvious in the whole parameter space, in addition to the global minimum of MSE at the default model parameter

モルモット ドウボウ ケッセツ サイボウ ニ オケル ベータ1 アドレナリン シゲキ ニ ヨル ヨウセイ ヘンジ サヨウ ノ イオン キジョ ニ ツイテ : シミュレーション ケンキュウ

京都大学0048新制・課程博士博士(医学)甲第13715号医博第3230号新制||医||967(附属図書館)UT51-2008-C632京都大学大学院医学研究科生理系専攻(主査)教授 大森 治紀, 教授 福田 和彦, 教授 成宮 周学位規則第4条第1項該当Doctor of Medical ScienceKyoto UniversityDA

The ‘way of flowers’ and the care of patients with amyotrophic lateral sclerosis in Japan

Tracheostomy with invasive ventilation (TIV) may be required for the survival of patients at advanced stages of amyotrophic lateral sclerosis (ALS). In Japan it has been shown that a proactive approach toward TIV may prolong the survival of ALS patients by over 10 years by preventing the lethal respiratory failure that generally occurs within 3-5 years of the onset of the disease. Measures to prolong life expectancy without foregoing quality of life have produced better results in Japan than in other developed countries. This ‘Japanese bias’ has been attributed to socio-cultural and religious factors as well as to the availability of material resources in Japan. In this article, we use the concepts of onozukara in kadō (Japanese traditional flower art, also called ikebana) and amae (passive love) to illuminate features of patient care that may contribute to this ‘Japanese bias’.La ventilación mecánica invasiva por traqueotomía (VMI) puede ser necesaria para la supervivencia de personas en la etapa avanzada de la esclerosis lateral amiotrófica (ELA). Se ha demostrado que un enfoque proactivo hacia la VMI en Japón posiblemente prolongue la supervivencia de los pacientes con ELA por más de 10 años al evitar la insuficiencia respiratoria letal que generalmente ocurre dentro de los 3 a 5 años del inicio de la enfermedad. En comparación con otros países desarrollados, Japón obtiene buenos resultados por lo que se refiere a prolongar la esperanza de vida sin sacrificar la calidad de vida. Este «sesgo japonés» (Japanese bias), como se lo ha llamado, se ha atribuido a factores socioculturales y religiosos, así como a los recursos materiales disponibles en el Japón. En este artículo, utilizamos los conceptos de onozukara en kadō (arte floral tradicional japonés, también llamado ikebana) y de amae (amor pasivo) para iluminar las características de la atención al paciente que podrían contribuir a producir el «sesgo japonés»

Clarifying the composition of the ATP consumption factors required for maintaining ion homeostasis in mouse rod photoreceptors

Abstract To date, no effective treatment has been established for photoreceptor loss due to energy imbalances, but numerous therapeutic approaches have reported some success in slowing photoreceptor degeneration by downregulating energy demand. However, the detailed mechanisms remain unclear. This study aimed to clarify the composition of ATP consumption factors in photoreceptors in darkness and in light. We introduced mathematical formulas for ionic current activities combined with a phototransduction model to form a new mathematical model for estimating the energy expenditure of each ionic current. The proposed model included various ionic currents identified in mouse rods using a gene expression database incorporating an available electrophysiological recording of each specific gene. ATP was mainly consumed by Na+/K+-ATPase and plasma membrane Ca2+-ATPase pumps to remove excess Na+ and Ca2+. The rod consumed 7 $$\times$$ × 107 molecules of ATP s−1, where 65% was used to remove ions from the cyclic nucleotide-gated channel and 20% from the hyperpolarization-activated current in darkness. Increased light intensity raised the energy requirements of the complex phototransduction cascade mechanisms. Nevertheless, the overall energy consumption was less than that in darkness due to the significant reduction in ATPase activities, where the hyperpolarization-activated current proportion increased to 83%. A better understanding of energy demand/supply may provide an effective tool for investigating retinal pathophysiological changes and analyzing novel therapeutic treatments related to the energy consumption of photoreceptors

Mechanisms underlying the volume regulation of interstitial fluid by capillaries: a simulation study

Background: Control of the extracellular fluid volume is one of the most indispensable issues for homeostasis of the internal milieu. However, complex interdependence of the pressures involved in determination of fluid exchange makes it difficult to predict a steady-state tissue volume under various physiological conditions without mathematical approaches. Methods: Here, we developed a capillary model based on the Starling's principle, which allowed us to clarify the mechanisms of the interstitial-fluid volume regulation. Three well known safety factors against edema: (1) low tissue compliance in negative pressure ranges; (2) lymphatic flow driven by the tissue pressure; and (3) protein washout by the lymph, were incorporated into the model in sequence. Results: An increase in blood pressure at the venous end of the capillary induced an interstitial-fluid volume increase, which, in turn, reduced negative tissue pressure to prevent edema. The lymphatic flow alleviated the edema by both carrying fluid away from the tissue and decreasing the colloidal osmotic pressure. From the model incorporating all three factors, we found that the interstitial-fluid volume changed quickly after the blood pressure change, and that the protein movement towards a certain equilibrium point followed the volume change. Conclusion: Mathematical analyses revealed that the system of the capillary is stable near the equilibrium point at steady state and normal physiological capillary pressure. The time course of the tissue-volume change was determined by two kinetic mechanisms: rapid fluid exchange and slow protein fluxes

A Novel Method to Quantify Contribution of Channels and Transporters to Membrane Potential Dynamics

The action potential, once triggered in ventricular or atrial myocytes, automatically proceeds on its time course or is generated spontaneously in sinoatrial node pacemaker cells. It is induced by complex interactions among such cellular components as ion channels, transporters, intracellular ion concentrations, and signaling molecules. We have developed what is, to our knowledge, a new method using a mathematical model to quantify the contribution of each cellular component to the automatic time courses of the action potential. In this method, an equilibrium value, which the membrane potential is approaching at a given moment, is calculated along the time course of the membrane potential. The calculation itself is based on the time-varying conductance and the reversal potentials of individual ion channels and electrogenic ion transporters. Since the equilibrium potential moves in advance of the membrane potential change, we refer to it as the lead potential, VL. The contribution of an individual current was successfully quantified by comparing dVL/dt before and after fixing the time-dependent change of a component of interest, such as the variations in the open probability of a channel or the turnover rate of an ion transporter. In addition to the action potential, the lead-potential analysis should also be applicable in all types of membrane excitation in many different kinds of cells