Identification of rhythmically active cells in guinea‐pig stomach

Abstract

Many organs containing smooth muscle are myogenically active. This was assumed to originate from activity within the individual smooth muscle cells. Some smooth muscle cells have low resting membrane potentials and generate myogenic activity, in much the same way as cardiac pacemaker cells, through the sequential activation of voltage-dependent ion channels (see for example Anderson, 1993). In others, myogenic activity originates from the cyclic release of calcium ions (Ca¥) from stores inside the smooth muscle cells (Van Helden, 1993;Hashitani et al. 1996). Many regions of the gastrointestinal tract generate slow waves and contract rhythmically at low frequencies in the absence of stimulation (Tomita, 1981;Sanders, 1992). Again it was initially thought that the generation of slow waves reflected some properties of gastrointestinal smooth muscle cells (Connor et al. 1974;El-Sharkaway & Daniel, 1975;Tomita, 1981). More recently it has been suggested that slow waves result from the interaction between two distinct groups of cells: one group acts as pacemaking cells and activates a second group which generates slow waves. Several observations suggest that activity originates in interstitial cells of Cajal (ICC), and that smooth muscle cells, rather than initiating activity, act as follower cells. ICC form diffuse networks of cells which are thought to be linked together as electrical syncytia (Thuneberg, 1982). When ICC lying near the submucous border of the circular muscle layer of dog colon are dissected away, nearby smooth muscles stop generating slow waves (Smith et al. 1987). Intestinal preparations taken from mice devoid of ICC fail to generate normal slow waves (Ward et al. 1994;Huizinga et al. 1995).

Unitary nature of regenerative potentials recorded from circular smooth muscle of guinea‐pig antrum

“…Effect of caffeine on regenerative potentials, membrane noise and unitary potentials recorded from single bundles of circular muscle from the antral region of guinea-pig stomach It has previously been shown that low concentrations of caffeine abolish both regenerative potentials and the secondary component of slow waves (Dickens et al 1999). In this series of experiments we examined the effects of low concentrations of caffeine on regenerative potentials and membrane noise and on unitary potentials detected in preparations that had been pretreated with BAPTA AM (10-20 ìÒ).…”

“…When caffeine (1 mÒ) was added to the physiological saline, the primary components of the slow waves persisted at low frequency ( Fig. 11B; see also Dickens et al 1999). These preparations had input resistances in the range 0·9-1·7 MÙ (1·4 ± 0·2 MÙ).…”

“…regenerative potential , so giving rise to the secondary component of the slow wave (Dickens et al 1999). During the resulting depolarization, L-type calcium channels (CaL channels) are activated but their contribution to the shape of a slow wave is barely detectable .…”

Interstitial cells of Cajal mediate mechanosensitive responses in the stomach

“…I n the stomach, electrical slow waves are generated by a specialized network of cells, known as interstitial cells of Cajal (ICC) , located in the myenteric region between the circular and longitudinal muscle layers (ICC-MY) (1)(2)(3). The stomach has a continuous network of ICC-MY from the orad corpus to the pyloric sphincter (1), and samples of muscle removed from each region demonstrate spontaneous activity that is characteristic of pacemaker cells in that region (4).…”

Effects of Transient Receptor Potential Channel Blockers on Pacemaker Activity in Interstitial Cells of Cajal from Mouse Small Intestine

“…The slow waves originate in the ICCs distributed in the GI tract (Dickens et al, 1999;Huizinga et al, 1995;Langton et al, 1989;Torihashi et al, 1995;Ordog et al, 1999;Ward et al, 1994). ICCs express c-kit immunoreactivity and form gap junctional connections with ICCs and with smooth muscle cells (Huizinga et al, 1997;Komuro et al, 1992;Sanders, 1996).…”