Background:

Synchronization of cellular activity states is being increasingly recognized as a crucial element determining organ function. Neural structures, interstitial cells of Cajal and smooth muscle cells interact to produce a specific temporal pattern of mechanical contractions that is controlled by changes in membrane potential. The smooth muscle of the RPV exhibits spontaneous contractions that are triggered by multi spike complexes (MSCs) consisting of a slow wave with superimposed fast spikes.

Methods:

Extracellular recordings of electrical and mechanical activity of isolated rat portal veins were done under physiological conditions and in the presence of the potassium channel blocking substances 4-Aminopyridine (4-AP) and Tetraethylammonium (TEA). The electrical signals of recorded MSCs were then processed offline by spectral analysis using a standard fast Fourier transform (FFT) algorithm.

Results:

TEA (n=8) and 4-AP (n=5) lead to a concentration-dependent increase in contraction-amplitude (in % of control +/- SEM; TEA: 1mM 146 +/-16, 3mM 164 +/-36, 10mM 190 +/-41; 4-AP: 0.3mM 184 +/-34, 1mM 230 +/-54, 3mM 302 +/-70). High-resolution spectral analysis of extracellular electrical activity revealed a dominant frequency of 7.08 Hz, corresponding to a period length of 142 ms which is consistent to the frequency of fast spikes seen with intracellular microelectrode measurements. An increase in power of this fundamental frequency was observed in 6 of 6 (100%) preparations tested with 4-AP and in 1 of 5 (80%) with TEA and was strongly correlated with contractile force.

Conclusions:

Spectral analysis can be used to identify fast spike events in extracellular recordings of spontaneous electrical activity of smooth muscle. When investigating the effects of substances acting on ion channels, changes in the spectrum of electrical events indicate improved electrical coupling as the basic mechanism of changes in contractile force. In case of the RPV, the augmentation of contractions that was observed after application of potassium channel blockers could clearly be attributed to an increased synchronization of electrical activity.