Application of Fourier linear spectral analyses to the characterization of smooth muscle contractile signals

In intestinal smooth muscle, peristaltic activity emerges from a depolarization wave generated by Cajal's interstitial cells that travels longitudinally and transversally towards adjacent smooth muscle. The electrophysiological diversity of cell populations involved in the generation and transmission of excitation between nerve and muscle cells, as well as the specialization in the excitation–contraction coupling of smooth muscle cells, makes it difficult to extrapolate individual cell responses to overall peristaltic activity. It is conceivable intestinal contractile activity as the macroscopic output from a multicellular system in time and frequency domains. Given that contractile signals are usually linear and stationary, application of frequency analyses using the discrete Fourier transform allows the accurate definition of amplitudes and phases of harmonic components in the frequency spectrum of contractile activity records, as well as the power spectrum of the signal. In addition, by using the short-time Fourier transform it is also possible to obtain the spectrogram of contractile signals, which allows the identification of non-stationary events. Often, the combined usage of these types of analyses together with specific pharmacological and molecular biology tools is sufficient to unveil the cellular and molecular locus of action of modulators of peristaltism, including hormones and different natural and synthetic compounds.