T channels

Riefe,/. groove, channel striation. riefeln, riefen, v.t. channel, groove knurl, mill rifle. 

In the sarcoplasm of resting muscle, the concentration of Ca + is 10 to 10 mol/L. The resting state is achieved because Ca + is pumped into the sarcoplasmic reticulum through the action of an active transport system, called the Ca + ATPase (Figure 49-8), initiating relaxation. The sarcoplasmic reticulum is a network of fine membranous sacs. Inside the sarcoplasmic reticulum, Ca + is bound to a specific Ca -binding protein designated calsequestrin. The sarcomere is surrounded by an excitable membrane (the T tubule system) composed of transverse (T) channels closely associated with the sarcoplasmic reticulum. 

Neither L nor T channels appear susceptible to the form of G-protein-mediated inhibition characteristic of N or P/Q channels. However, as in the heart cells, L-type Ca +... 

Figure 2.9 Hyperpolarisation-activated cation current 4 and its role in pacemaking in a guinea-pig thalamic relay neuron. (Adapted from Figs 2 and 14 in McCormick, DA and Pape, H-C (1990) J. Physiol. 431 291-318. Reproduced by permission of the Physiological Society.) (a) Records showing the time-dependent activation of the h-current by hyperpolarisation and its deactivation on repolarising, (b) Interpretation of rhythmic activity in a thalamic relay neuron. (1) The inter-spike hyperpolarisation activates 7h to produce a slowly rising pacemaker depolarisation. (2) This opens T-type Ca " channels to give a more rapid depolarisation, leading to (3) a burst of Na" spikes (see Fig. 2.8). At (4) the depolarisation has closed (deactivated) the h-channels and has inactivated the T-channels. The membrane now hyperpolarises, assisted by outward K+ current (5). This hyperpolarisation now removes T-channel in-activation and activates 7h (6), to produce another pacemaker potential...

Although ubiquitin-conjugation of receptors in mammalian cells has been observed, the function of this modification seems less clear. In the case of the growth hormone receptor (GH-receptor) and the epithelial Na-t- channel (ENaC), it seems likely that ubiquitin-conjugation triggers their endocytosis. 

This micro mixer, named electrohydrodynamic (EHD) microfluidic mixer, comprises a simple T-channel structure (see Figure 1.5) [91]. After passing the T-junction, a bi-laminated stream is realized. Following a downstream zone for such flow establishment, a channel zone with several electrode wires on both sides of the channel is located. In this way, an electric field perpendicular to the fluid interface is generated. Thereafter, an electrode-free zone of the channel is situated for completion of the mixing initiated. 

Figure 1.5 Schematic of the electrohydrodynamic mixer with T-channel and pairs of electrodes adjacent to the channel and perpendicular to the fluid interface generated [91] (by courtesy of RSC).

P 24] Computer simulations were carried out using the software Fluent 6 [68], A 3-D solid model of the T-channel micro mixer was built and named in Gambit The simulations were made solely for the zone of the T-junction, since for all other zones, including the downstream section of the mixing channel, laminar flow was assumed. Thus, a fine mesh of 173 000 brick elements could be used for the solid model. 

Detailed visualization of flow patterns at the start and end of a T-channel - liquid mixing... 

Table 1.3 Liquid mixing times for T-channel micro mixers of varying hydraulic diameter [68].

Table 1.4 Dimensionless values for the intensity of mixing at the outlet face of the T-channel micro mixer for the six scenarios simulated [68].

Figure 1.55 Scenario 1 symmetric flow rates lead to symmetric flow fields giving an overall two-layered fluid structure with hardly any species penetration and a low degree of mixing, (a) and (b) show fluid trajectories of one species for the cross-sectional area at the mixing channel front and the whole T-channel design (c) gives a mass-fraction contour plot of the other species at the outlet face [68] (by courtesy of Elsevier Ltd.).

The channel structure of the mixer is a simple cross, i.e. four channels which all merge at one junction [71]. A cross was preferred over a T-channel mixer since two interfaces instead of only one are initially created when the fluids are contacted. The top channel feeds one fluid, while the other fluid is injected via the left and right channels. The last, bottom channel functions as mixing and outlet zone. Squares, much smaller than the channel width, are positioned at the walls of this mixing channel and function as static mixing elements. The squares are positioned on alternate sides of the channels and at a distance corresponding to multiple square widths. 

M 80] [P 70] The mixing performance of three mixing devices was characterized by a pH-indicator reaction using phenolphthalein a T-channel, slanted grooved... 

Figure 1.166 Normalized average intensity changes along the down-channel direction of three micro-mixer devices with barrier-embedded, slanted grooved and T-channel structures at (a) Re = 0.228, (b) 0.457, (c) 0.685 and (d) 2.28 [58] (by courtesy of IOP Publishing Ltd ).

M 85] [P 75] In order to determine reaction kinetics by a stopped-flow method, the mixing step within a microfluidic system was improved [161]. Traditionally, an efficient external T-channel mixer is used for this purpose. Now, the bimodal intersecting channel micro mixer was integrated into the system. The mixer has the following advantages over the current state of the art ... 

Figure 1.178 Stopped-flow enzymatic assays when using an external T-channel micro mixer, the bimodal intersecting channel micro mixer and the flow before the micro mixer with only diffusion mixing [161 ]...

These plates are inserted in a T-channel structure in a still thicker plate, directly at the T-junction at the ends of the two feed channels. In this way, a rectangular mixing chamber is formed in the outlet channel of the T-structure, having multinozzle arrays on both sides. The arrays can be positioned with and without offset to collide the jets directly and to let them flow aside. In the latter case, it is thought that eddies are produced at sufficiently high velocity of the jets. 

FIGURE 3.40 (a) Configuration of the experimental setup and white light microscopy image of an imprinted T-channel with a series of ablated wells, (b) Fluorescence images of electroosmotic flow past the mixer at flow rates of 0.06 cm/s [193]. Reprinted with permission from the American Chemical Society. 

FIGURE 9.23 Optical micrograph of a T-channel device used for DNA separation. The... 

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