Signal processing smoothing functions

Some SR compartments (jSR) lie just beneath special microdomains of PM, and are joined to this PL by electron-dense processes (observed with electron microscopy). Na+ pumps with high-ouabain-affinity a. subunits (a2/a3 subunits), NCX and SOCs, appear to be confined to these PL microdomains. These PL microdomains, the subjacent jSR, and the intervening tiny cytosolic volume, form functionally specialized units we call PLasmERosomes. Through the operation of these units (which are apparently present in many types of cells), modulation of Na+ pump activity may have a profound influence on Ca2+ signalling in smooth muscles and many other types of cells. 

Each signal processing method discussed here involves same function which is either interpolating or smoothing, and is either local or global approximation of the data. This results in the two-way classification of the methods shown in Figure 4.2, where the quadrants of each card list methods of the same family for the particular application. 

Although numerical differentiation is considered as a routine step in signal processing, our discussion tries to emphasize that its results heavily depend on the choice of the interpolating or smoothing function. Different methods may lead to much deviating estimates. Nevertheless, from frequently sampled data we may be able to locate extrema or inflection points by numerical differentiation, since zero-crossing of the first or second derivatives is somewhat more reliable than their values. 

Thus the role of the SR in the uterus can be seen to incorporate excitability via Ca2+-activated channels, as well as releasing some Ca2+ to support agonist-induced contractions. As with other smooth muscles it is necessary to consider the spatiotemporal nature of the Ca2+ signals produced, if we are to fully understand the ultimate functional effects on contraction. So far the discussion has focussed on the elevation of the Ca2+ signal with stimulation. We will now consider the equally important process of lowering Ca2+ and its role in relaxation in the uterus. 

FIGURE 10.12 Time-domain smoothing of the noisy data in Figure 10.1 with the impulse response function of Figure 10.7, processed from left to right in this spectrum. The true signal is shown as a dotted line. Note the significant filter lag in this example. 

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