China
Africa
Explore chapters and articles related to this topic
39K
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Similarly to sodium, potassium is therefore a vital component of the human body. The potassium ion K+ is an important electrolyte that helps maintain the homeostasis of the organism through osmoregulation and pH regulation. It is also involved in cell physiology through the transmembrane electrochemical gradient, in heart activity, and in the transmission of nerve impulses and muscle contractions through propagation of action potential in neurons and muscle cells via the potassium channels. In contrast to sodium, which is mostly extracellular, potassium is the main intracellular ion for all types of cells, with concentrations of 4–10 mM in extracellular fluids and 120–140 mM inside the cells. Cells in healthy tissues need to maintain this large potassium concentration gradient between the intracellular and extracellular compartments across the cell membrane to control cell volume and membrane potential through many ionic pumps, channels, and other transporters. Any impairment of energy metabolism or insult to the cell membrane integrity can lead to dysregulation of these ionic transporters and of the membrane potential, leading to a decrease in intracellular potassium concentration and/or a local increase in extracellular potassium concentration.
First Pass at Supramolecular Structures
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
A voltage-gated potassium (K+) ion channel in membranes is an example of a protein aggregate with three types of subunits. Figure 6.9 shows the dodecameric (12-subunit) membrane potassium channel KcsA-Fab protein aggregate. Three distinct polypeptides each occur 4 times in this aggregate. The α-helical, intramembrane part of the aggregate can be identified at the top in Figure 6.9b. Potassium ions diffuse across the cell membrane in a single file through the narrow selectivity filter of potassium channels. The structure of the channel shows the chemical structure of the selectivity filter is due to four K+ binding sites. There are 40 known human voltage-gated potassium channel alpha (membrane spanning) proteins.
Basic Electrophysiology
Published in Joseph D. Bronzino, Donald R. Peterson, Biomedical Engineering Fundamentals, 2019
ese channels are dynamic, opening and closing stochastically. Each channel contains four gating elements, historically called particles. When open, which is more likely when the transmembrane potential is more positive, potassium channels allow potassium ions to pass from the inside to the outside of the membrane. Potassium channels do not allow other ion species, such as sodium ions to pass, except to a minor degree. Selective movement of potassium ions from the inside to the outside of the membrane creates the negative resting transmembrane voltage when the cell is at rest, as explained in detail in the following section. Potassium channels have four gating elements (called n gates) within each channel. All have to be open for the channel to be open. Each gating element opens and closes stochastically and apparently independently, to a good approximation.
Model-guided concurrent data assimilation for calibrating cardiac ion-channel kinetics
Published in IISE Transactions on Healthcare Systems Engineering, 2023
Haedong Kim, Hui Yang, Andrew R. Ednie, Eric S. Bennett
Potassium channels (Kv) play critical roles in the electrical conduction system of the heart, particularly in the repolarization phase of the action potential (AP). The AP is a change of membrane potential over time, representing the net electrical activity in a cardiomyocyte, and the AP shape and duration are primarily determined by Kv isoforms. The ability of the heart to pump blood through the body in an appropriate rhythm is controlled by electrical signaling. Hence, even modest changes in Kv activities can significantly affect the AP duration and the QT interval, which lead to fatal heart diseases (Ravens & Cerbai, 2008). As shown in Fig. 1, the different phases of AP repolarization in mouse cardiomyocytes are the result of the coordinated activity of a variety of Kv isoforms (e.g. Kv4.2, Kv1.5, and Kv2.1) and their corresponding currents (e.g. IKto, IKslow1, and IKslow2). There are other major voltage-gated ion channels (VGICs), such as for Na+ (Nav) and Ca2+ (Cav), that also contribute to the AP. The Nav are primarily responsible for the AP upstroke in the depolarization phase, while the Cav control the cellular contraction. Aberrant activities of ion channels can significantly impact the AP and lead to fatal arrhythmias. Using whole-cell voltage-clamp recording methods, only the collective activities of Kv isoforms can be measured reliably as the sum of all K+ currents (IKsum), and these Kv isoforms have overlapping biophysical properties (i.e. voltage dependence of gating and kinetics), which complicate the ability to separate one type of IK from another (Brouillette et al., 2004). Kv activities can be altered in various cardiomyopathies (Giudicessi & Ackerman, 2012; Tristani-Firouzi et al., 2001), thus there is an urgent need to decompose IKsum more rigorously into individual K+ currents and estimate gating kinetics of Kv isoforms to understand their pathological roles by comparing their activities in healthy versus diseased hearts and cardiomyocytes.