Endocytosis and exocytosis

Affinity tor K ions decreases and affinity tor Na ions increases 

In addition, the presence of glucose in the tubules increases the osmotic pressure which pulls water from the blood into the tubule. Consequently, both glucose and water are lost from the body. This results in polyuria, dehydration, thirst and, hence, polydipsia. Indeed, it is these two symptoms that may persuade an unsuspecting diabetic to seek medical advice. 

One additional benefit is that by continuously pumping more Na ions out than K+ ions into the cell, it results in a higher intracellular K+ ion concentration than might be expected. Since the K+ ion channel is open, the K+ ions diffuse out to an extect dependent upon the concentration difference, so that the Na+/K+ ATPase contributes to the magnitude of the membrane potential across a cell. 

When some cells are observed under a microscope, regions of the plasma membrane can be seen to fold into the cell, forming pockets that pinch off to produce membrane-bound vesicles within the cell. This is the means by which 

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Figure 41-16. A comparison of the mechanisms of endocytosis and exocytosis. Exocytosis invoives the contact of two inside surface (cytopiasmic side) mono-iayers, whereas endocytosis resuits from the contact of two outer surface mono-iayers.

Single-particle tracking of endocytosis and exocytosis of single-walled carbon nanotubes in NIH-3T3 cells. Nano Letters, 8 (6), 1577-1585. 

The second myosin type identified in nervous tissue was the myosin I family. It was first described in protists and subsequently purified from brain. Myosin I is a singleheaded myosin with a short tail that uses calmodulin as a light chain [41]. In many cell types it has been implicated in both endocytosis and exocytosis, so it may play an important role in delivery and recycling of receptors. Myosin I is enriched in microvilli and may also be involved in some aspects of growth cone motility along with... 

Niles WD, Malik AB. Endocytosis and exocytosis events regulate vesicle traffic in endothelial cells. J Membr Biol 1999 167(1) 85-101. 

A process similar to endocytosis occurs in the reverse direction when it is known as exocytosis (Figure 5.11). Membrane-bound vesicles in the cytosol fuse with the plasma membrane and release their contents to the outside of the cell. Both endocytosis and exocytosis are manifestations of the widespread phenomenon of vesicular transport, which not only ferries materials in and out of cells but also between organelles, e.g. from the endoplasmic reticulum to the Golgi and then to the lysosomes or to the plasma membrane for secretion (Chapter 1). Many hormones are also secreted in this way, as are neurotransmitters from one nerve into a synaptic junction that joins two nerves (Chapters 12 and 14). 

Specific proteins mediate the fusion of two membranes, which accompanies processes such as viral invasion and endocytosis and exocytosis. 

By virtue of their size and charge, peptide molecules are not the ideal candidates for transfer into the systemic circulation following instillation in the nose. Among the many barriers to absorption that must be overcome are mucociliary clearance, extracellular enzymatic destruction, the lipophilic bilayer membrane of nasal epithelial cells, the potential for nasal epithelial cells to degrade any peptide molecules that cross the lipid bilayer, and the potential to establish futile cycles of endocytosis and exocytosis on the apical surface of polarized epithelial cells. Indeed, in the face of these multiple barriers, it seems all the more remarkable that any substantial absorption of peptide drugs from the nose has ever been observed. Despite these barriers, recent... 

H. Tomoda, Y. Kishimoto, and Y. C. Lee, Temperature effect on endocytosis and exocytosis by rabbit alveolar macrophages, J. Biol. Chem. 264 15445-15450 (1989). 

Microtubules and microfilaments are ubiquitous components of almost all cells (red blood cells excluded). Microfilaments are polymers of actin, which in the non-muscle cell can exist in two forms /3-actin and T-actin. Microfilaments have a diameter of about 6 nm. In certain structures such as the microvilli of intestinal mucosal cells, microfilaments are associated with myosin, so that movement is possible given an appropriate stimulus. Endocytosis and exocytosis events are apparently mediated via microfilaments. Microfilaments are disrupted by the drug cytochalasin. 

Vesicles — (i) In cell biology, a vesicle is a small enclosed compartment, separated from the cytosol of a eukaryotic cell by a membrane of fatty acids. Vesicles are responsible for the transport of various compounds across cell membranes by endocytosis and - exocytosis. 

Panyam, J. and Labhasetwar, V. (2003) Dynamics of endocytosis and exocytosis of poly(D,L-lactide-co-glycolide) nanopartides in vascular smooth musde cells. Pharmaceutical Research, 20, 212-220. 

It is now clear that protein kinase C-catalyzed phosphorylation of specific cellular proteins plays an essential role in the orchestration of the biochemical events responsible for cellular activation. Some of the cellular proteins phosphory-lated by protein kinase C are listed in Table 1. The effects of protein kinase C-mediated phosphorylation include the modulation of ion channels and ion pumps, alterations in cellular endocytosis and exocytosis (e.g., the release of neurotransmitters and humoral agents), and modulation of gene expression and cellular proliferation. 

A FIGURE 17-34 Transcytosis of maternal IgG immunoglobulins across the intestinal epithelial cells of newborn mice. This transcellular movement of a ligand involves both endocytosis and exocytosis. The one-way movement of ligand from the intestinal lumen to the blood depends on the differential affinity of the Fc receptor for antibody at pH 6 (strong binding) and at pH 7 (weak binding). Transcytosis in the opposite direction returns the empty Fc receptor to the luminal membrane. See text for discussion. 

Allison, A. C., Davies, P. Mechanisms of endocytosis and exocytosis, in Transport at the Cellular Level, Society for Exp. Biol. Symp, xxvili, p. 419, Cambridge, Cambridge University Press 1974... 

ADP-Rlbosylatlon Factor 6 Regulation of Phosphatidyllnosltol-4,5-Bisphosphate Synthesis, Endocytosis, and Exocytosis... 

Arf6 regulation of PIP2 synthesis, endocytosis, and exocytosis 423... 

Arf6 REGULATION OF PIP2 SYNTHESIS, ENDOCYTOSIS, AND EXOCYTOSIS 431... 

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