Cells transmembrane

Kozin, S.V., Shkarin, P. and Gerweck, L.E. (2001) The cell transmembrane pH gradient in tumors enhances cytotoxicity of specific weak acid chemotherapeutics. Cancer Res., 61, 4740 1743. 

Stimulation of B cells to proliferate and differentiate into memory and plasma cells depends on epitope binding to epitope-specific receptors on CD4+ T-helper cells. Transmembrane signaling then requires the coreceptor protein CD3. Binding of the T-cell receptor to the antigen-presenting B cell occurs via the TcR that interacts with... 

This Nemst relationship can be applied to living cell membranes. Cells are most permeable to potassium, and if we substitute known concentration values of potassium inside and outside the cell, we find that the cell transmembrane potential is near this value, but not exactly. 

The Goldman equation accounts for multiple ionic contributors to the cell membrane potential. It assumes that the membrane permeability P is equivalent to the internal resistance of an ionic battery. Thus, with multiple ionic species that all contribute, the cell transmembrane potential is given by... 

Tanner, M. K. Wellhausen, S. R. Flow cytometric detection of fluorescent redistributional dyes for measurement of cell transmembrane potential. Methods Mol Biol 1998, 91, 85-95. 

Cystic fibrosis, a disease of the Caucasian population, is associated with defective CL regulation and is essentially a disorder of epithehal cells (113,114). The defect arises at several levels in the CL ion transporter, ie, the cystic fibrosis transmembrane regulation (CFTR), and is associated with defective CL transport and defective processing, whereby the protein is not correctiy incorporated into the cell membrane. The most common mutation, affecting approximately 60% of patients, is termed F 608 and designates the loss of phenylalanine at this position. This mutation appears to be at least 50,000 years old, which suggests that its survival may have had evolutionary significance (115). 

Retention, too, is highly tissue-specific. Sometimes, the extraction mechanism is also the retention mechanism, as for Tc-sestamibi, which is retained in mitochondria as long as transmembrane potentials remain intact. Others are separate. F-2-Fluorodeoxyglucose enters the cell by the same pathway as glucose, but is trapped because it is not a substrate for hexokinase, preventing further intracellular metabohsm. 

Verapamil (Table 1), the first slow channel calcium blocker synthesized to selectively inhibit the transmembrane influx of calcium ions into cells, lowers blood pressure in hypertensive patients having good organ perfusion particularly with increased renal blood flow. Sustained-release verapamil for once a day dosing is available for the treatment of hypertension. Constipation is a prominent side effect. Headache, dizziness, and edema are frequent and verapamil can sometimes cause AV conduction disturbances and AV block. Verapamil should not be used in combination with -adrenoceptor blockers because of the synergistic negative effects on heart rate and contractile force. 

The C-terminal transmembrane helix, the inner helix, faces the central pore while the N-terminal helix, the outer helix, faces the lipid membrane. The four inner helices of the molecule are tilted and kinked so that the subunits open like petals of a flower towards the outside of the cell (Figure 12.10). The open petals house the region of the polypeptide chain between the two transmembrane helices. This segment of about 30 residues contains an additional helix, the pore helix, and loop regions which form the outer part of the ion channel. One of these loop regions with its counterparts from the three other subunits forms the narrow selectivity filter that is responsible for ion selectivity. The central and inner parts of the ion channel are lined by residues from the four inner helices. 

T-cell receptors (TCR) are heterodimeric transmembrane glycoproteins found exclusively in T cells, with extracellular domains that closely resemble antibody Fab structures. Each of the TCR a and p chains forms half of an extracellular antigen-binding domain, and in addition has one transmembrane... 

These interactions involve adhesion proteins called selectins, which are found both on the rolling leukocytes and on the endothelial cells of the vascular walls. Selectins have a characteristic domain structure, consisting of an N-terminal extracellular lectin domain, a single epidermal growth factor (EGR) domain, a series of two to nine short consensus repeat (SCR) domains, a single transmembrane segment, and a short cytoplasmic domain. Lectin domains, first characterized in plants, bind carbohydrates... 

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