Outward transport

FIGURE 21.32 Outward transport of ATP (via the ATP/ADP transloease) is favored by the membrane electrochemical potential. 

The plasma membrane Ca2+-ATPase pump effects outward transport of Ca2+ against a large electrochemical gradient for Ca2+. The mechanism of the pump involves its phosphorylation by ATP and the formation of a high-energy intermediate. This basic mechanism is similar for both the plasma membrane and ER pumps however, the structures of these distinct gene products are substantially different. As discussed below, the ER pump, sometimes called a sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) pump, is inhibited potently by certain natural and synthetic toxins that do not affect the plasma membrane pump. The plasma membrane pump, but not the SERCA pump, is controlled in part by Ca2+ calmodulin, allowing for rapid activation when cytoplasmic Ca2+ rises. 

C. B. Engler, B. Sander, M. Larsen, P. Koefoed, H. H. Parving, and H. Lund-Andersen. Probenecid inhibition of the outward transport of fluorescein across the human blood-retina barrier. Acta Ophthalmol. 72 663-667 (1994). 

All diuretics inhibit Na+ reabsorp-tioa Basically, either the inward or the outward transport of Na+ can be affected. 

Nerve stimulation results in a net influx of sodium ions, and normal conditions are restored by the outward transport of sodium ions against an electrochemical gradient. While several earlier workers had identified ATPases in the sheath of giant squid axons, it was Skou who first connected the sodium, potassium ATPase [EC 3.6.1.37] with the ion flux of neurons. This discovery culminated... 

Net carrier transport can be examined whenever a transportable substrate is present on both sides of a membrane. Again for the case of a single class of carriers, the inward transport rate and outward transport rates show rate-saturation behavior ... 

The exact mechanism by which the depolarization leads to movement of the voltage sensor is not known. A simple model is under discussion, in which the S4 helix turns outwards by one helix turn during opening and thus leads to outward transport of 1—2 charges. A more complex model assumes a conformational change of the S4 helix in which the outward transport of charges is associated with conversion of a a-helix into a P-sheet structure. 

TFP (5) was the first phenothiazine demonstrated to modulate MDR in drug-resistant P338 murine leukemia cells. TFP (5) enhanced intracellular accumulation of vincristine and adriamycin (77) in resistant tumor cells by inhibiting outward transport of these anticancer drugs [167]. Studies per-... 

Dano K. Active outward transport of daunomycin in resistant Ehrlich ascites tumor cells. Biochim Biophys Acta 1973 323 466 483. 

There is evidence from chondrites that the solar nebula was well mixed between 0.1 and 10 AU during its first several million years of the evolution, as shown by the homogeneity in concentrations of many isotopes of refractory elements (Boss 2004 Chapter 9). This is likely caused by the evaporation and recondensation of solids in the very hot inner nebula, followed by outward transport due to turbulent diffusion and angular momentum removal. Materials out of which terrestrial planets and asteroids are built have been heated to temperatures above 1300 K and are thus depleted in volatile elements. The inner solar nebula, with some exceptions, does not retain memories of the pristine interstellar medium (ISM) chemical composition (Palme 2001 Trieloff Palme 2006). 

Chen N, Justice JB (2000) Differential effect of structural modification of human dopamine transporter on the inward and outward transport of dopamine. Mol Brain Res 75 208-215... 

Fig. 3 Schematic representation of iontophoresis. Two electrode chambers, connected to a power source, are placed in contact with the skin. Upon application of the electric field, drug ions are repelled from the electrode of similar polarity (in this case, cations are repelled from the anode). This electrorepulsion (ER) also imposes inward motion on i) other cations present in the anode formulation, and ii) the outward transport of anions (e.g., CP) from within the skin. At the non-working electrode (in this case, the cathode), negative anions from the electrolyte are driven into and through the skin, while cations (e.g., Na ) are extracted from the tissue. The direction of the electroosmotic flow (EO) is also shown.

Although the phenomenon of multidrug resistance of bacteria was observed more than fifty years ago, it took 20 years until the first drug transporter, P-glycoprotein, was discovered as the responsible cellular factor for the outward transport of xenobiotics of different chemical structure. Another ten years later, experimental results on different tumor cell lines indicated that P-glycoprotein also occurs in advanced cancers and plays a major role in contributing to the non-response to chemotherapy. 

Excretion. Although direct evidence exists for outward transport of inorganic ions across the cuticle of A. suum (127), little is known about the relative importance of the cuticle, intestine or putative excretory canal system in nematodes for outward transport of metabolic end-products or other organic molecules. Organic acid end-products of carbohydrate metabolism are excreted across the cuticle in A. suum (129) and H. contortus (123). This process generates a microclimate pH within the aqueous pores of the cuticle which is maintained at pH 5.0, near the pK of the excreted organic acids (130). 

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