Influx rate

Tab. 5.12 Effect of chemosensitizers on taxol influx rates and steady-state levels of cellular taxol accumulation in parental and MDR hamster cells. (Reprinted from Tab. 3 of ref. 109 with permission from Blackwell Science)...

Cell line Modulator Initial taxol influx rate (pmol 10"6) cells min" Taxol accumulation (pmol/106 cells)... 

Taxol influx rates that were linear for the first 60 s are given as the initial influx rates. Numbers in parentheses describe the relative initial rates and accumulation levels of taxol obtained in the presence of modulators compared with their absence. The taxol accumulation values were obtained after 1 h incubation. 

Fig. 14.11 Length distributions of the fragments outside the proteasome. From left to right the efflux rate e increases e = (0.1, 1, 10). Each distribution has been taken at the time 170 (a), 86 (b), 76 (c) when 20 % of substrate degraded. The vertical on each plot is the log frequency (from 0 to 0.25). The influx rate a = 0.01. Note that the distributions are insensitive to the variation in the influx rate a [27],...

When a typical cell is activated by a hormone, or other extracellular messenger, a common event is a 2-4-fold increase in Ca2+ influx rate through Ca2+ channels in the plasma membrane [1]. Such an increase in Ca2+ influx rate leads to only a transient increase in cellular Ca2+ concentration [Ca2+]j, because of the existence of an... 

When hepatocytes are exposed to a low concentration of glucagon (1012 M), the hormone interacts with one class of receptors linked to phospholipase C and the hydrolysis of PIP2 [26]. These events lead to an increase in Insl,4,5P3, and presumably to both a mobilization of intracellular Ca2+ and an increase in Ca2+ influx rate. Hence, low concentrations of glucagon act exclusively via the PI system. 

The conclusions from this analysis are (a) that Ca2+ influx rate (and hence Ca2+ cycling) is the prime determinant of the magnitude of a sustained cellular response in cells whose response is controlled via the Ca2+ messenger system and (b) this is true whether the particular response is mediated via the synarchic interaction of Ca2+ and cAMP, or by the coordinate, Ca2+-dependent regulation of CaM-dependent protein kinases and protein kinase C [31]. 

This obvious dependence on extracellular calcium is somewhat unexpected because (1) the sustained enhancement of calcium influx rate is adequately balanced by an increase in calcium efflux rate so that (2) the calcium concentration in the bulk cytosol is maintained near the basal value. This apparent paradox may be resolved by a model [54] which postulates that during the sustained phase of cellular response the high rate of calcium cycling across the plasma membrane raises the calcium concentration in a region just below the plasma membrane, often called the submembrane domain (see Rasmussen and Barrett, Chapter 4). Because the elevated calcium level in this domain is not conducted into the bulk cytosol, it cannot activate calcium-dependent response elements in the cytosol. Rather it regulates the activity of calcium-sensitive, plasma membrane-associated enzymes such as the calcium pump and PKC, the previously described phospholipid-dependent, calcium-activated protein kinase. 

Figure 9-11. Valve-like properties of the upper layer of a loamy soil under dry versus wet conditions (a) a dry crust and (b) wh ile being wet by rain. Water is lost gradually across the dry crust but readily enters the wet soil. Water movement is also influenced by gravity, the x elevant component of the water potential (pwgh) decreasing by 0.01 MPa per meter depth in the soil. For a depth of 5 mm, the gravitational contribution decreases 4 by 0.00005 MPa compared to thesoil surface, which increases the influx rate by 25% for the wet condition compared to considering only AP, as is done here (the influence of the 0.00005 MPa gravitational component is negligible for the diy condition).

Adrenal medullary cells have plasma membrane receptors for acetylcholine (ACh) of the neuronal nicotinic subtype (Nn). These receptors are cation channels that span the plasma membrane and are activated by ACh to rapidly increase Na" " and K+ permeabilities (Na" " influx rate 5 x 10 ions/s), causing the cells to depolarize and release their catecholamines by exocytosis. The cholinergic stimulation of exocytosis is accompanied by an activation of tyrosine hydroxylase activity within the adrenal medullary cell, and this promotes biosynthesis of... 

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