Mobility buffer

As both fast and slow adaptation mechanisms are regulated by Ca2+, the stereocilia mechanisms that control the free concentration of this ion also play central roles in transduction. Entering Ca2+ is thought to be buffered very rapidly by the mobile buffers parvalbumin 3, calbindin, and calretinin [22,23]. Even before bound Ca2+ can diffuse out of stereocilia, it is pumped back out into the endo-lymph by isoform 2a of the plasma-membrane Ca2+-ATPase (PMCA2) [24,25] (see also Ca2+ transport in Ch. 5). 

Nelson Relating to the proximity, we have probed this area by looking at sparks and the communication in the large conductance Ca2+-activated K+ (BK) channels. The measurements are consistent with close apposition of the RyRs and spark sites to the BK channels. This would be consistent with a proximity of 10—20 nm seen by electron microscopy. Also, mobile buffers are unable to compete with Ca2+ at the BK channel, which is also consistent with this idea. As a probe of what happens to local Ca2+ we have looked at the decay of a spark. Nothing we could do, such as zero Na+ or lanthanum, had any effect on the decay, suggesting that diffusion was responsible. 

FIG. 3. Tight coupling in cardiac but not smooth muscle myocytes. Cells dialysed with 17 nM mobile Ca2+ buffer (EGTA). When depolarized, brief Ca2+ release events are seen in ventricular myocytes, indicating RyR gating occurs before the mobile buffer can scavenge the gating Ca2+ ions. Conversely, in smooth muscle cells CICR is completely blocked. The simplest interpretation of these data is that Ca2+ ions must traverse a distance of at least lOOnm, the distance beyond which the mobile buffer can prevent a rise in Ca2+. (From Collier et al 2000.)... 

Kotlikoff Because the mobile buffer is not quick enough to block this. 

Where D is the apparent Ca2+ diffusion coefficient, D is the true diffusion coefficient in water, Ks is the buffer dissociation constant, and B is the concentration of the buffer. For a detailed analysis of Ca2+ diffusion in the presence of fixed and mobile buffers, see Wagner Keizer (1994). 

As a rule, hydrogen ion is involved not only in the pH-dependency of the reaction term (Thiele modulus) but also as the actively participating species involved in the acid-base equilibrium of all the substrates, reaction intermediates, products, and even the gel matrix. Furthermore, enzymatic reactions are always carried out in the presence of the mobile buffer. By mobile we mean a weak acid or a weak base that can move in and out of the reaction layer, as opposed to the fixed buffer represented by the gel (and by the protein) itself. Thus, we have to include the normalized diffusion-reaction equations for hydrogen ion and for the buffer. 

Injection HPLC Dilute with mobile buffer - 35 ml MSA ... 

JuNGE, W., McLaughlin, S., The role of fixed and mobile buffers in the kinetics of proton movement, Biochim. Biophys. Acta, 1987, 890, 1—5. 

Figrrre 3 can be used to represent the micellar-polymer process. A certain volume of the micellar or smfactant solution fltrid A is injected into the reservoir. The smfactant solution is then followed by a polymer solution, fltrid B, to provide a mobility buffer between the sttrfac-tant solution and a drive water, which is used to push the entire system through the reservoir. The polymer solution is designed to prevent viscous Angering of the drive... 

CD, low mobility buffers with higher ionic strengths provide an extended linearity and improve preconcentration by sample stacking. 

GUPTA, S.P. and TRUSHENSKI, S.P. "Micellar Flooding - The Propagation of the Poljnner Mobility Buffer Bank", SPEJ, 1978, 5,... 

Laboratory studies on oil displacement efficiency by surfactant-polymer flooding process have been reported by a number of investigators (1-10). In general, the process is such that after being conditioned by field brine or preflush, a sandstone core or a sandpack is oil-saturated to the irreducible water content. It is then waterflooded to the residual oil level. Finally, a slug of surfactant solution followed by a mobility buffer is injected. 

The basic apparatuses for FIAEC and LCEC are shown in Figure 4. The two are identical except that for LCEC a chromatographic column is included between its injection port and detector. In both FIAEC and LECE, the sample is introduced to the system via the injection valve, whereupon the mobile buffer carries the sample through the electrochemical detector downstream. The most popular type of electrochemical detector is the commercially available thin-layer flow cell of 1-20 pL volume whose design provides optimum flow characteristics and a high electrode surface-area-to-ceU-volume for sensitive detection. 

The feed solution is normally introduced into the mobile buffer solution at z = 0 of a continuous ffee-flow electrophoresis (CFE) apparatus in a thin band of width 2S in the y-direction (Figure 7.3.2(a)). If assumption (2) of plug flow of buffer in the z-direction were truly valid, the preceding analyses (e.g. result ((7.3.6)) would hold also for a solute band of width 2S, i.e. the band will appear undeformed but displaced by EnfL/Vz) in the x-direction. 

Fig, 5.98—Injection schedule for graded mobility buffer, North Burbank surfactant test. ... 

Costs prohibit continuous injection of the mobility buffer. At some point in the displacement process, sufficient polymer has been injected to prevent the drive water from fingering through the mobility buffer into the chemical slug. A region of variable concentration forms owing to mixing between the drive water and the polymer. If the polymer concentration in the mobility buffer remains constant, the size of the mobility buffer needed to protect the chemical slug can be estimated from experimental displacement runs or from mathematical models. 

Bank size may be determined experimentally. Results of a mixing-zone study done in a 16-ft Berea sandstone core illustrate one approach. In this study, glycerine, biopolymer, and polyacrylamide solutions of various mobilities were displaced through the core by drive water. The length of the mixing zone was determined from effluent concentrations to be the volume between the 5 % and 95 % concentrations. Fig. 5.96 summarizes the results. The mixing-zone volume is a function of mobility ratio, as would be expected. For example, the mobility buffer must be 0.5 PV to prevent reduction... 

Fig. 5.98 36 shows the injection schedule for polymer concentration in the mobility buffer for tbe North Burbank surfactant field test. The total amount of polymer injected was 0.7 PV at an average concentration of 710 ppm. The quantity of polymer is equivalent to a 0.2-PV slug of polymer at a concentration of 2,500 ppm, which is at the leading edge of the mobility buffer. 

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