Contrast enhancement agents and radiopharmaceuticals
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha in Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
The cell membrane represents a barrier to the passage of material into the cell. Movement of radiopharmaceuticals may occur passively by diffusion down an electrochemical gradient, e.g. in lipid-soluble transport. This is a slow process and some structures are impermeable to all but the most essential materials. The blood–brain barrier is a classic example of this. However, if it is disrupted by a pathological process, radiopharmaceuticals such as pertechnetate are able to pass into the area of damage. More rapid mechanisms of transport are mediated by specialised structural components in the cell membrane. Facilitated diffusion results in the rapid transfer of substances along the electrochemical gradient; active transport results in movement against a concentration gradient involving the use of adenosine triphosphate (ATP) as a source of energy. Figure 2.24a demonstrates an axial slice from a 99mTc-hexamethylpropyleneamine oxime (HMPAO) scan.
Reconstituted Membrane Systems for Assaying Membrane Proteins in Controlled Lipid Environments
Qiu-Xing Jiang in New Techniques for Studying Biomembranes, 2020
Cell membranes play a pivotal role in separating cells from their environments, maintaining cells in an off-equilibrium steady state, detecting and relaying outside signals into the cells by responding to their environments in specific manners. There has been a strong interest in the scientific community because membrane systems, including both membrane proteins and lipids, are fundamentally important for all live cells, and serve as therapeutic targets for human diseases. Membrane proteins generally include both integral membrane proteins that are integrated in a membrane and traverse both leaflets of the bilayer and peripheral membrane proteins that are associated with lipids or proteins in membranes.1,2 Around 20%–30% of identified proteins of the human genome are predicted integral membrane proteins.3–6 Although the total number of integral membrane proteins is increasing over time, determination of the structural basis for their functions still lags behind. In particular, it remains difficult to study quantitatively the effects of membrane lipids on the structure and function of membrane proteins.
Cell Structure and Functions
Malgorzata Lekka in Cellular Analysis by Atomic Force Microscopy, 2017
The external boundary of a cell is provided by a membrane [1]. It is not only a passive barrier separating a cell from an environment but it actively participates in various phenomena needed for cell functioning. Membranes provide a tool to maintain cell integrity and also they divide internal cellular space into compartments, where, sometimes, quite contradictory processes occur. The biological activity of cell membrane are a result of its structure and exclusive physical properties. Cell membrane is highly flexible, which enables relatively fast changes in cellular shape observed, for example, during cell division or cell migration. Due to selective permeability, cellular membrane regulates the transport of certain molecules and ions to cell interior/exterior, within a cell, and also within a specific cellular compartment. Cell membrane contains a variety of molecules and proteins participating in various cellular processes. At the cell surface, some proteins are responsible for the cell-to-extracellular matrix and for cell-to-cell interactions while the other ones move specific organic solutes and inorganic ions across the membrane. When situated inside the cell, various membranes take part in such processes as lipid synthesis or energy transduction in mitochondria [1].
Recent advances in ultrasound-triggered therapy
Published in Journal of Drug Targeting, 2019
Chaopin Yang, Yue Li, Meng Du, Zhiyi Chen
Being a plasma membrane, cell membrane is a barrier to isolate the internal and external environments of cells. However, sonication combined UCAs can cause transient damage to the cell membrane and further results in temporary and reversible holes (Figure 2), which provides a channel for extracellular substances coming into the cell through the cell membrane [28]. Early in 1999, Tachibana et al. observed that the cell membrane underwent porous changes after being treated by ultrasound combing MBs by scanning electron microscope (SEM). It can also boost the absorption of extracellular substances by affecting the endocytosis of cells [29]. A series of following studies have confirmed that ultrasound or ultrasound combined with MBs could improve the permeability of cell membrane through sonoporation to facilitate the entry of extracellular substances into the cell [30,31].
Evaluation of the antimicrobial mechanism of biogenic selenium nanoparticles against Pseudomonas fluorescens
Published in Biofouling, 2023
Ying Xu, Ting Zhang, Jiarui Che, Jiajia Yi, Lina Wei, Hongliang Li
The integrity of the cell membrane is a key factor in bacterial growth. In normal cells, proteins are the main macromolecules present in the cell membrane. The cell membrane not only keeps the cell environment stable for energy and substance metabolism it also regulates and selects substances that enter and leave the cells. The integrity of the membrane can be assayed by the leakage of the cell contents. This study showed that that as the SeNPs concentration increased, the OD gradually increased, and the leakage of proteins and nucleic acids in P. fluorescens ATCC 13525 increased in a time-dependent manner. It was speculated that SeNPs reacted with thiols or sulfhydryl groups in phospholipid bilayer membrane proteins to denature and inactivate them, leading to the loss of the integrity of cell membrane and an increase in membrane permeability. Tareq et al. (2017) found that SeNPs promoted protein leakage from the bacterial cytoplasm, which was 6.10 μg mg−1 in the control group, while after treatment with SeNPs, it was increased to be 7.12 μg mg−1. The live/dead state of bacteria was observed by CLSM. It was found that the live cells gradually decreased and the dead cells increased when treated with SeNPs, indicating that the cell membrane was damaged. Similarly, Ning et al. (2021) found that phenyllactic acid significantly compromised the cell membrane integrity of P. fluorescens.
Profiling gene expression dynamics underpinning conventional testing approaches to better inform pre-clinical evaluation of an age appropriate spironolactone formulation
Published in Pharmaceutical Development and Technology, 2021
Craig Russell, Majad Hussain, David Huen, Ayesha S. Rahman, Afzal R. Mohammed
When considering permeability through the intestinal epithelial, it is important to consider the inherent properties which limit absorption. This includes the physiochemical makeup of the cell membranes as well as the tight junctions between the cells which are tightly regulated and highly selective. For instance, SLC9A3R1 is of interest when examining intestinal permeability as it codes for SLC9A3 Regulator 1 (NHERF1). This protein interacts with villin and actin which function as linkers between integral membrane and cytoskeletal proteins involved with the formation and maintenance of tight junctions (Castellani et al. 2012). Tight junctions exist between intestinal enterocytes and are one of the key limiters in modulating paracellular intestinal permeability and maintaining membrane barrier function. Although spironolactone is not reported to be absorbed paracellularly this may indicate that tight junctions were closed in response to exposure to the spironolactone formulation. Evidence of cellular response to formulation exposure can also be seen through expression changes in genes involved in signalling pathways including SLC25A6, SLC3A2, SLC7A5, SLC27A1, and SLC2A2. cGMP-PKG signalling has been shown previously to control dynamic responses of tight junctions in the blood brain barrier (BBB) through voltage-dependent anion channel protein 1 which is coded for by SLC25A6 (González-Mariscal et al. 2008). The tight junctions that form the paracellular barrier at the BBB and intestinal enterocytes display remarkable molecular similarities (Daneman and Rescigno 2009).
Related Knowledge Centers
- Cytoplasm
- Extracellular Space
- Integral Membrane Protein
- Lipid Bilayer
- Membrane Fluidity
- Membrane Protein
- Phospholipid
- Cholesterol
- Biological Membrane
- Cell