Biomedical subjects

J D Huizinga

Publications and source records attributed to J D Huizinga.

At least 55 records · Page 3Linked to original sources

PubMed1998

Interstitial cells of cajal direct normal propulsive contractile activity in the mouse small intestine.

BACKGROUND & AIMS: Interstitial cells of Cajal (ICC) have been linked to the generation of intestinal pacemaker activity, but their role in in vivo motor dysfunction is unclear. In this study, we investigated the hypothesis that ICC play a role in the generation of distention-induced peristalsis using W/Wv mice that lack ICC associated with Auerbach's plexus. METHODS: Radiological observations were made of the movement of contrast fluid through the proximal small intestine. Electrical activities were recorded in the external muscle layers. In addition, intraluminal pressure changes were recorded in isolated intestinal segments. RESULTS: In control mice, after gavage of 0.5 mL of barium sulfate in the stomach, the contrast fluid moved through the proximal small intestine in peristaltic waves at approximately 47 times a minute, propagating aborally at approximately 2 cm/s. Electrical slow waves and intraluminal pressure waves were synchronized at similar frequencies and propagation velocities. In W/Wv mice, such regular peristaltic waves were not observed. Action potentials and contractions appeared random, and contents moved back and forth in an irregular manner. The net propulsive effect of contractile activity in W/Wv mutant mice was much weaker than that in controls. CONCLUSIONS: Slow wave controlled peristalsis occurs in the normal proximal small intestine upon gastric emptying of a semiliquid. This motor pattern is absent in W/Wv mice that lack ICC.

Animals↗

PubMed1998

Interstitial cells of Cajal generate a rhythmic pacemaker current.

Networks of interstitial cells of Cajal embedded in the musculature of the gastrointestinal tract are involved in the generation of electrical pacemaker activity for gastrointestinal motility. This pacemaker activity manifests itself as rhythmic slow waves in membrane potential, and controls the frequency and propagation characteristics of gut contractile activity. Mice that lack a functional Kit receptor fail to develop the network of interstitial cells of Cajal associated with Auerbach's plexus in the mouse small intestine and do not generate slow wave activity. These cells could provide an essential component of slow wave activity (for example, a biochemical trigger that would be transferred to smooth muscle cells), or provide an actual pacemaker current that could initiate slow waves. Here we provide direct evidence that a single cell, identified as an interstitial cell of Cajal by light microscopy, electron microscopy and expression of Kit mRNA, generates spontaneous contractions and a rhythmic inward current that is insensitive to L-type calcium channel blockers. Identification of the pacemaker of gut motility will aid in the elucidation of the pathophysiology of intestinal motor disorders, and provide a target cell for pharmacological treatment.

Animals↗

PubMed1998

Action potential generation, Kit receptor immunohistochemistry and morphology of steel-Dickie (Sl/Sld) mutant mouse small intestine.

In contrast to wild-type mice, homozygotes with mutations of the W locus do not express the functional Kit receptor and are severely deficient in the Auerbach's plexus (AP)-associated subtype of interstitial cells of Cajal (ICC-AP). With a morphologically intact neural and muscular structure, the absence in these mutants of both small-intestinal slow waves and ICC-AP constitutes strong evidence for a key role of ICC-AP as pacemaker cells. In steel-Dickie mutant mice (Sl/Sld), the gene coding for the Kit ligand (stem cell factor) is defective. We examined Sl/Sld mutants and controls with intracellular microelectrode techniques, combined with light and electron microscopy. The absence of the normal Kit ligand (Sl/Sld mice) had very similar effects as the absence of the Kit receptor in viable mice, mutated at the White spotting, W, locus (W/Wv mice), in that neither slow waves, nor Kit receptor immunoreactivity in the region of Auerbach's plexus nor ICC-AP were present in the small intestine. In the Sl/Sld mouse, the smooth muscle cells generated action potentials at variable frequencies from a depolarized cell membrane of -40 to -55 mV. Increasing excitability by K channel blockers created many different patterns of action potential generation and the frequency increased from approximately 16 cpm to 66 cpm. This was in sharp contrast to control mice where action potentials were always restricted to the plateau phase of the slow waves and the slow wave frequency remained constant at approximately 39 cpm. Our data provide further strong support for the identification of ICC-AP as small-intestinal pacemaker cells. In addition, they provide a basis for the understanding of intestinal motor function without pacemaker activity.

Action Potentials↗

PubMed1998

Neural injury, repair, and adaptation in the GI tract. IV. Pathophysiology of GI motility related to interstitial cells of Cajal.

Our understanding of the physiological roles played by interstitial cells of Cajal (ICC) in relation to gastrointestinal (GI) motility is still rudimentary. Nevertheless, studies into the pathophysiology of ICC are emerging at a rapid pace. Caution should be exercised, however, in assuming correlations between changes in Kit immunoreactivity, findings of ultrastructural abnormalities in ICC, and the pathophysiology and symptoms of the patients. Recent studies have revealed reduced numbers or the absence of ICC in small intestine and colon that do not exhibit normal peristaltic activity. Furthermore, important evidence is emerging that motor abnormalities in newborns may be associated with delayed maturation of the ICC network. These preliminary clinical studies provide plausible hypotheses toward the pathophysiology of certain motor disorders and strongly encourage basic scientific studies directed toward discovering the intrinsic properties of ICC as well as obtaining a deeper understanding of the physiological roles played by these cells.

Adaptation, Physiological↗

PubMed1997

Interstitial cells of Cajal as targets for pharmacological intervention in gastrointestinal motor disorders.

Interstitial cells of Cajal (ICCs) have recently been identified as the pacemaker cells for contractile activity of the gastrointestinal tract. These cells generate the electrical 'slow-wave' activity that determines the characteristic frequency of phasic contractions of the stomach, intestine and colon. Slow waves also determine the direction and velocity of propagation of peristaltic activity, in concert with the enteric nervous system. Characterization of receptors and ion channels in the ICC membrane is under way, and manipulation of slow-wave activity markedly alters movement of contents through the gut organs. Here Jan Huizinga, Lars Thuneberg, Jean-Marie Vanderwinden and Jüri Rumessen, suggest that, as ICCs are unique to the gut, they might be ideal targets for pharmacological intervention in gastrointestinal motility disorders, which are very common and costly.

Animals↗

PubMed1997

Pinaverium acts as L-type calcium channel blocker on smooth muscle of colon.

The effect of pinaverium was electrophysiologically characterized and compared with the established L-type calcium channel blockers diltiazem, D600, and nitrendipine on canine colonic circular smooth muscle. Effects were studied on the electrical activity of the smooth muscle cells, in particular the spontaneously occurring slow wave. In addition, effects were examined on spontaneous contraction patterns and contractile activities generated by stimulation of cholinergic nerves or directly by stimulating muscarinic receptors. Effects were also examined on excitation of NO-releasing intrinsic nerves. Pinaverium bromide affected the slow wave by selectively inhibiting the plateau potential that is associated with generation of contractile activity. Pinaverium, similar to diltiazem and D600, produced reductions in cholinergic responses as well as spontaneous contractions. The IC50 values for inhibition of cholinergic responses for pinaverium, diltiazem, and D600 were 1.0 x 10(-6), 4.1 x 10(-7), and 5.3 x 10(-7) M, respectively. The IC50 values for inhibition of spontaneous contractile activity for pinaverium, diltiazem, and D600 were 3.8 x 10(-6), 9.7 x 10(-7), and 8.0 x 10(-7) M, respectively. Increases in contractility by carbachol were abolished by pretreatment with either pinaverium or D600. In addition, neither pinaverium nor D600 had any effects on the inhibitory NO-mediated relaxations. These data provide a rationale for the use of pinaverium in the treatment of colonic motor disorders where excessive contraction has to be suppressed.

Animals↗

PubMed1997

Inflammation modulates in vitro colonic myoelectric and contractile activity and interstitial cells of Cajal.

Inflammation suppresses phasic contractile activity in vivo. We investigated whether inflammation also suppresses in vitro phasic contractile activity and, if so, whether this could in part be due to the alteration of specific slow wave characteristics and morphology of the interstitial cells of Cajal (ICC). Circular muscle strips were obtained from normal and inflamed distal canine colon. Inflammation was induced by mucosal exposure to ethanol and acetic acid. The amplitudes of spontaneous, methacholine-induced, substance P-induced, and electrical field stimulation-induced contractions were smaller in inflamed muscle strips than in normal muscle strips. Inflammation reduced the resting membrane potential and the amplitude and duration of slow waves in circular muscle cells. Inflammation did not affect the amplitude of inhibitory junction potentials but did decrease their duration. Ultrastructural studies showed expansion of the extracellular space between circular muscle cells, reduction in the density of ICC and associated neural structures, damage to ICC processes, vacuolization of their cytoplasm, and blebbings of the plasma membrane. We conclude that inflammation-induced alterations of slow wave characteristics contribute to the suppression of phasic contractions. These alterations may, in part, be due to the damage to ICC. Inflammation impairs both the myogenic and neural regulation of phasic contractions.

Acetic Acid↗

PubMed1997

Circular muscle lamellae of canine colon are electrically isolated functional units.

The circular muscle (CM) layer of canine colon consists of circumferentially oriented lamellae separated by connective tissue septa. These lamellae facilitate circumferential ring contractions. Communication between CM lamellae is necessary to generate coordinated, propulsive phasic contractions to create peristaltic movement. Potential roles of the submuscular network of interstitial cells of Cajal and branching smooth muscle cells (ICC-bSM), the myenteric interstitial cells of Cajal network (ICC-AP), and the longitudinal muscle (LM) layer in mediating communication between the CM lamellae were studied by simultaneously recording with three surface electrodes, using different types of muscle strip preparations. When the ICC-bSM network was intact, slow waves were observed to be entrained both along and across CM lamellae. In contrast, the CM layer devoid of the ICC-bSM network, the myenteric plexus, and the longitudinal muscle (CM preparation) was spontaneously quiescent. Spike-like action potentials, evoked in the CM preparations by Ba2+ (0.5 mM), were entrained within CM lamellae but were not coordinated between the CM lamellae. In the LM-CM preparations, in which the longitudinal muscle and the ICC-AP network were intact, the Ba(2+)-evoked action potentials were again not coordinated across septa but entrained within CM lamellae. In a step preparation, in which the ICC-bSM network was removed from part of the muscle strip, slow waves were observed to be entrained in areas with and without the ICC-bSM network when electrodes were positioned along septa. When electrodes were positioned across CM lamellae, synchronized slow wave activity was observed only in areas with the intact ICC-bSM network and quiescent activity was recorded in areas devoid of the ICC-bSM network. These results demonstrate that CM cells are electrically coupled within a CM lamella, but not between CM lamellae. The submuscular ICC-bSM network, but not longitudinal or circular muscle cells, nor the ICC-AP, mediates communication between CM lamellae.

Animals↗

PubMed1996

P2x-purinoceptors of myenteric neurones from the guinea-pig ileum and their unusual pharmacological properties.

1. Whole-cell and outside-out patch clamp recordings were used to characterize the physiological and pharmacological properties of the P2x-purinoceptors of myenteric neurones from the guinea-pig ileum. 2. Adenosine 5'-triphosphate (ATP) and analogues (1-3000 microM) evoked a rapid inward current in > 90% of all recorded neurones. The reversal potential of this current was dependent on the extracellular sodium concentration, at +14 +/- 1.9, 0 +/- 1.6 and -12 +/- 1 mV for 166, 83 and 42 mM of sodium, respectively. The fast activation and inactivation of this current occurred even when guanosine 5'-triphosphate (GTP) was omitted from the pipette solution or substituted with an equimolar concentration of guanosine 5'-o-[2-thiotriphosphate] (GTP-gamma-S). Single channel currents were observed when these outside-out membrane patches were exposed to ATP (10-30 microM). These channels have a unitary conductance of about 17 picosiemens. 3. The rank-order of potency of the agonists used to induce the whole-cell currents was: ATP-gamma-S = ATP = 2-methylthio-ATP (2-Me-S-ATP) > > alpha, beta-methylene ATP = beta, gamma-methylene ATP; adenosine and uridine 5'-triphosphate (UTP) (up to 1 mM) were inactive. 4. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (1-30 microM) antagonized the effects of ATP (1 mM) with an IC50 of 4 microM. alpha, beta-Methylene ATP (100 microM) did not affect the ATP (30 microM)-induced current. Cibacron Blue 3GA increased the ATP activated cationic current whereas Basilen Blue E-3G had a very weak antagonistic effect (IC50 > or = 3 mM). Suramin potentiated the currents induced by ATP through a mechanism that was independent of its inhibitory effect on ectonucleotidase activity, as suramin also potentiated the effect of alpha, beta-methylene ATP (an ATP analogue that is resistant to nucleotidases). 5. In conclusion, the myenteric P2x-purinoceptor shares some properties with other purinoceptors in particular with the P2x4- and P2x6-purinoceptors. This receptor has also some unusual pharmacological properties suggesting that myenteric neurones express a novel subtype of P2x-purinoceptors. The properties of this receptor, however, might be a result of the combination of two or more of the homomeric purinoceptors so far characterized.

Adenosine Triphosphate↗

PubMed1996

Action potential generation in the small intestine of W mutant mice that lack interstitial cells of Cajal.

The small intestine of W/Wv mice lacks both the network of interstitial cells of Cajal (ICC), associated with Auerbach's plexus, and pacemaker activity, i.e., it does not generate slow-wave-type action potentials. The W/Wv muscle preparations showed a wide variety of electrical activities, ranging from total quiescence to generation of action potentials at regular or irregular frequency with or without periods of quiescence. The action potentials consisted of a slow component with superimposed spikes, preceded by a slowly developing depolarization and followed by a transient hyperpolarization. The action potentials were completely abolished by L-type Ca2+ channel blockers. W/Wv mice responded to K+ channel blockade (0.5 mM Ba2+ or 10 mM tetraethylammonium chloride) with effects on amplitude, frequency, rate of rise, and duration of the action potentials. In quiescent tissues from W/Wv mice, K+ channel blockade evoked the typical spikelike action potentials. Electron microscopy identified few methylene blue-positive cells in the W/Wv small intestine associated with Auerbach's plexus as individual ICC. Numbers of resident macrophage-like cells (MLC) and fibroblast-like cells (FLC) were significantly changed. Neither FLC nor MLC were part of a network nor did they form specialized junctions with neighboring cells as ICC do. Hence no cell type had replaced ICC at their normal morphological position associated with Auerbach's plexus. ICC were present in W/Wv mice at the deep muscular plexus in normal organization and numbers, indicating that they are not dependent on the Kit protein and do not take part in generation of pacemaker activity.

Action Potentials↗

PubMed1995

W/kit gene required for interstitial cells of Cajal and for intestinal pacemaker activity.

The pacemaker activity in the mammalian gut is responsible for generating anally propagating phasic contractions. The cellular basis for this intrinsic activity is unknown. The smooth muscle cells of the external muscle layers and the innervated cellular network of interstitial cells of Cajal, which is closely associated with the external muscle layers of the mammalian gut, have both been proposed to stimulate pacemaker activity. The interstitial cells of Cajal were identified in the last century but their developmental origin and function have remained unclear. Here we show that the interstitial cells of Cajal express the Kit receptor tyrosine kinase. Furthermore, mice with mutations in the dominant white spotting (W) locus, which have cellular defects in haematopoiesis, melanogenesis and gametogenesis as a result of mutations in the Kit gene, also lack the network of interstitial cells of Cajal associated with Auerbach's nerve plexus and intestinal pacemaker activity.

Action Potentials↗

PubMed1995

Generation of slow wave type action potentials in the mouse small intestine involves a non-L-type calcium channel.

Intrinsic electrical activities in various isolated segments of the mouse small intestine were recorded (i) to characterize action potential generation and (ii) to obtain a profile on the ion channels involved in initiating the slow wave type action potentials (slow waves). Gradients in slow wave frequency, resting membrane potential, and occurrence of spiking activity were found, with the proximal intestine exhibiting the highest frequency, the most hyperpolarized cell membrane, and the greatest occurrence of spikes. The slow waves were only partially sensitive to L-type calcium channel blockers. Nifedipine, verapamil, and pinaverium bromide abolished spikes that occurred on the plateau phase of the slow waves in all tissues. The activity that remained in the presence of L-type calcium channel blockers, the upstroke potential, retained a similar amplitude to the original slow wave and was of identical frequency. The upstroke potential was not sensitive to a reduction in extracellular chloride or to the sodium channel blockers tetrodotoxin and mexiletine. Abolishment of the Na+ gradient by removal of 120 mM extracellular Na+ reduced the upstroke potential frequency by 13 - 18% and its amplitude by 50 - 70% in the ileum. The amplitude was similarly reduced by Ni2+ (up to 5 mM), and by flufenamic acid (100 mu M), a nonspecific cation and chloride channel blocker. Gadolinium, a nonspecific blocker of cation and stretch-activated channels, had no effect. Throughout these pharmacological manipulations, a robust oscillation remained at 5 - 10 mV. This oscillation likely reflects pacemaker activity. It was rapidly abolished by removal of extracellular calcium but not affected by L-type calcium channel blockers. In summary, the mouse small intestine has been established as a model for research into slow wave generation and electrical pacemaker activity. The upstroke part of the slow wave has two components, the pacemaker component involves a non-L-type calcium channel.

Action Potentials↗

PubMed1995

Intercellular metabolic coupling in canine colon musculature.

Intercellular communication within the musculature of the canine colon was studied by examining the results of neurobiotin diffusion after injection of the tracer into smooth muscle cells at different locations within the muscle layer. Circular muscle at the submucosal surface, circular muscle adjacent to the myenteric plexus, and longitudinal muscle demonstrated different degrees of time-dependent tracer spread. At the submucosal surface, tracer spread was rapid, extensive, and unimpeded by connective tissue septa. At the myenteric side, tracer spread was also extensive but was much slower and confined to bundles of cells bordered by septa. In contrast to previous studies that suggest an absence of gap junctions at the myenteric side of the circular muscle, the neurobiotin spread indicates full metabolic coupling of all circular smooth muscle cells. Furthermore, in contrast to the belief that longitudinal muscle is completely devoid of gap junctions, tracer spread occurred between cells in this layer, although neurobiotin diffusion was very limited, nonuniform, and slow. In each area of the musculature studied, tracer spread was inhibited by octanol. When very long injection and wait times were implemented at the submucosal surface of the circular muscle, neurobiotin was observed to cross septa through the network of interstitial cells of Cajal, indicating that it is this network that provides communication between lamellae.

Action Potentials↗

PubMed1995

Cyclopiazonic acid, inhibiting the endoplasmic reticulum calcium pump, reduces the canine colonic pacemaker frequency.

The slow wave frequency of the canine colon has previously been hypothesized to be paced by an intracellular biochemical clock. We investigated the relationship between the endoplasmic reticulum (ER) Ca++ and the periodicity of the biochemical clock. Cyclopiazonic acid, a specific inhibitor of the ER Ca++ pump, dose-dependently decreased the pacemaker frequency. Similarly, chelating cytosolic Ca++ with bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetra-acetic acid (BAPTA) also decreased the pacemaker frequency. These observations suggest that delaying the Ca++ uptake into the ER decreases the pacemaker frequency. The pacemaker frequency was similarly decreased by neomycin [inhibiting inositol 1,4,5-triphosphate (IP3) synthesis] and by caffeine at concentrations higher than 5 mM (inhibiting the IP3-sensitive Ca++ channels in the ER membrane). Hence the IP3-sensitive Ca++ stores are involved in the biochemical clock. Ryanodine (up to 60 microM) did not affect the pacemaker frequency, which indicates that a ryanodine-sensitive store, if it exists, is not coupled to the biochemical clock. Electron microscopy showed that the smooth ER forms an extensive network of subsurface cisternae that is closely associated with large areas of the cytoplasmic face of the plasma membrane. These structures were the most extensive in interstitial cells of Cajal, slightly less in branching smooth muscle cells and far less in circular muscle cells. In summary, on the basis of these electrophysiological and morphological observations, we hypothesize that the Ca++ refilling cycle of the IP3-sensitive calcium stores associated with the plasma membrane determines the frequency of the pacemaker activity generated by the submuscular interstitial cells of Cajal-smooth-muscle network of the canine colon.

Action Potentials↗

PubMed1994

Canine colonic circular muscle generates action potentials without the pacemaker component.

Two dominant types of action potentials in canine colon are slow wave type action potentials (slow waves) and spike-like action potentials (SLAPs). The slow waves, originating at the submuscular surface where a network of interstitial cells of Cajal (ICCs) is found, possess a pacemaker component. Activation of the pacemaker component is insensitive to voltage changes and L-type calcium channel blockers, and is postulated to involve a metabolic clock sensitive to cyclic AMP. SLAPs are more prominent in the longitudinal muscle. To understand the contribution circular muscle cells make to the generation of these action potentials, a circular muscle preparation (devoid of the submuscular ICC-smooth muscle network, longitudinal muscle, and myenteric plexus) was developed. Circular muscle preparations were spontaneously quiescent, with a resting membrane potential of -62.9 +/- 0.6 mV. Ba2+ (0.5 mM) depolarized the cells to -51.8 +/- 0.6 mV and induced electrical oscillations with a frequency, duration, amplitude, and rate of rise equal to 6.6 +/- 0.4 cpm, 2.2 +/- 0.2 s, 19.4 +/- 0.9 mV, and 21.8 +/- 1.7 mV/s, respectively. In most cases, Ba(2+)-induced oscillations were preceded by a prepotential of 4.4 +/- 0.3 mV, with a rate of rise of 1.1 +/- 0.1 mV/s. Ba(2+)-induced oscillations were abolished by 1 microM D600 as well as by repolarization of 6-12 mV. Addition of 0.1 microM Bay K8644 in the presence of Ba2+ further depolarized circular muscle cells to -42.4 +/- 0.8 mV and increased the oscillation frequency to 16.8 +/- 1.8 cpm. The electrical oscillations induced in circular muscle preparations by Ba2+ and Bay K8644 were similar to the SLAPs exhibited by the isolated longitudinal muscle layer, indicating that generation of SLAPs is an intrinsic property of smooth muscle cells. Forskolin (1 microM), previously shown to dramatically decrease the frequency but not the amplitude of slow waves in preparations including the submuscular ICC network, decreased the amplitude of the Ba(2+)-induced oscillations in circular muscle preparations without changing the frequency. These results provide strong evidence for the hypothesis that the submuscular ICC-smooth muscle network is essential for the initiation of the pacemaker component of the colonic slow waves. The mechanism for regulating the frequency of slow waves is different from that responsible for the Ba(2+)-induced oscillations in circular muscle preparations. Circular muscle cells are shown to be excitable and capable of generating oscillatory activity dominated by L-type calcium channel activity, which is regulated by K+ conductance.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1994

Ultrastructure of interstitial cells of Cajal in the canine distal esophagus.

The ultrastructure of canine distal esophagus was studied focusing on interstitial cells of Cajal (ICC) and their relationships to nerves and muscle. The distal esophagus consisted of two muscle layers composed of intertwining skeletal and smooth muscle bundles. The ICC formed an interconnecting network and were an integral part of these structures. The ICC communicated with one another and with adjacent smooth muscle cells through numerous gap junctions. The morphology of individual ICC resembled that observed in other gut regions. All interstitial cells were densely innervated. The highest density of ICC, just proximal to the lower esophageal sphincter, coincided with the previously reported highest incidence of occurrence of electrical slow wave type action potentials. Examination of a large number of structural associations of ICC led us to conclude that in the distal esophagus, two networks of ICC and nerves exist, one associated with the inner muscle layer, another associated with the outer muscle layer. These networks are not sheet-like structures, such as the network of ICC in the myenteric plexus or deep muscular plexus of the small intestine, but are three dimensional and are interspersed throughout both muscle layers. The networks do not extend into Auerbach's plexus. The main branches of the networks run along the long axis of the esophagus and seem ideally suited to facilitate communication in this direction. These observations suggest that esophageal interstitial cells are structurally organized in such a manner that they may play a role in pacemaking and neural control of esophageal motility.

Animals↗

PubMed1994

Relaxation oscillator and core conductor models are needed for understanding of GI electrical activities.

This review examines the applicability of modeling of intestinal electrical activities (slow waves or pacesetter potentials) by coupled relaxation oscillator models, in comparison to a "multidimensional model" based on core conductor theory. We briefly review the relaxation oscillator model and correct some misunderstandings. We point out that new insights about the role of networks of interstitial cells of Cajal in intestinal pacemaking require reconsideration of the mechanisms producing oscillations, the coupling between oscillators, and how the oscillator network is coupled to the driven cells. Recent advances in relaxation oscillator models allow the production of pacemaking pacemaking activity, which can be selectively varied as to waveform, frequency, and occurrence of silent periods. Core conductor models do not produce pacemaking activity or permit this flexibility. We point out that many of the criticisms leveled against relaxation oscillator models relate to studies made in simplified in vitro systems constrained by extensive dissection. Such systems do not adequately reflect the in vivo systems. We conclude that a full understanding of control of electrical (and mechanical) events in the gastrointestinal tract requires that better understanding of relaxation oscillator models growing out of recent research be combined with improved applications of core conductor theory to multidimensional models.

Animals↗

PubMed1994

Selective lesioning of interstitial cells of Cajal by methylene blue and light leads to loss of slow waves.

Incubation with 50 microM methylene blue (MB) and subsequent intense illumination resulted in abolition of the slow-wave activity in the submuscular interstitial cells of Cajal-circular muscle (ICC-CM) preparations of canine colon. This was often accompanied by a decrease in resting membrane potential. Repolarization of cells back to -70 mV did not restore the slow-wave activity, indicating that MB plus light directly interrupted the generation mechanism of slow waves. After MB incubation, a 2-min illumination consistently changed the mitochondrial conformation in ICCs from very condensed to orthodox, without inducing any obvious changes in smooth muscle cells. After 4- to 10-min illumination, ICCs became progressively more damaged with swollen and ruptured mitochondria, loss of cytoplasmic contrast and detail, loss of caveolae, and rupture of the plasma membrane. No damage was seen in smooth muscle cells or nerves. Gap junctional ultrastructure was preserved. Intense illumination without preincubation with MB left the slow waves and the ultrastructure of ICC-CM preparations unaffected. In CM preparations, without the submuscular ICC-smooth-muscle network, MB plus light induced no changes in electrical activity. We conclude that the correlation between selective damage to the submuscular ICCs (relative to smooth muscle) and selective loss of the slow-wave activity (relative to other electrical activity of the CM) strongly indicates that the ICCs play an essential role in the generation of slow waves.

Animals↗