Calcium-associated mechanisms in gut pacemaker activity

Abstract

A considerable body of evidence has revealed that interstitial cells of Cajal (ICC), identified with c-Kit-immunoreactivity, act as gut pacemaker cells, with spontaneous Ca(2+) activity in ICC as the probable primary mechanism. Namely, intracellular (cytosolic) Ca(2+) oscillations in ICC periodically activate plasmalemmal Ca(2+)-dependent ion channels and thereby generate pacemaker potentials. This review will, thus, focus on Ca(2+)-associated mechanisms in ICC in the gastrointestinal (GI) tract, including auxiliary organs.

1

The action sites of drugs on Ca²⁺-associated mechanisms in ICC pacemaker activity. ICC and SM in this figure represent interstitial cells of Cajal and smooth muscle cells, respectively. For other abbreviations, see text.

2

ICC [Ca²⁺]_i oscillations synchronized with mechanical (A) and electrical (B) activities in cell cluster preparations isolated from the muscle layer of the murine small intestine. This figure was made by modifying Figure 2 of [44] and Figure 4 of [27]. (A): Ca²⁺ images (fluo-3 fluorescence) obtained from a cell cluster preparation with a high intensity area that could be used to monitor mechanical activity. Panels (a) and (b) are pseudo-colour Ca²⁺ images acquired at basal and peak times of an initial oscillation cycle in normal solution, respectively. The mechanical activity (c: movement) was estimated by tracking the high intensity area indicated by the arrow in (a). The time course of [Ca²⁺]_i oscillations (d) was measured in the square region (red line) of the cell cluster preparation shown in (a). After this recording, using a K⁺ channel opener to suppress smooth muscle activity, we confirmed that ICC produced the Ca²⁺ activity in the square region [44]. The fluorescence is expressed relative to that at the initial basal time: F_t/F₀.(B) Field potential (a) and fluo-4 fluorescence (b) were measured simultaneously in a cell cluster preparation in the presence of nifedipine which differentiates ICC activity by suppressing smooth muscle activity [27]. Thick and thin lines in (b) represent ICC and non-ICC regions of a cell cluster preparation, respectively.

3

Plausible mechanisms linking spontaneous [Ca²⁺]_i oscillations and pacemaker potentials in ICC.