Expression and function of KCNH2 (HERG) in the human jejunum

2003 ◽  
Vol 284 (6) ◽  
pp. G883-G895 ◽  
Author(s):  
A. M. Farrelly ◽  
S. Ro ◽  
B. P. Callaghan ◽  
M. A. Khoyi ◽  
N. Fleming ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Interstitial Cells Of Cajal ◽  
Circular Muscle ◽  
Slow Waves ◽  
Enteric Neurons ◽  
Longitudinal Smooth Muscle ◽  
Low Concentrations ◽  
Pair Sequence ◽  
And Function ◽  
Cells Of Cajal

Previous studies suggest that ether-a-go-go related gene (ERG) KCNH2 potassium channels contribute to the control of motility patterns in the gastrointestinal tract of animal models. The present study examines whether these results can be translated into a role in human gastrointestinal muscles. Messages for two different variants of the KCNH2 gene were detected: KCNH2 V1 human ERG (HERG) (28) and KCNH2 V2 (HERGUSO) (13). The amount of V2 message was greater than V1 in both human jejunum and brain. The base-pair sequence that gives rise to domains S3– S5 of the channel was identical to that previously published for human KCNH2 V1 and V2. KCNH2 protein was detected immunohistochemically in circular and longitudinal smooth muscle and enteric neurons but not in interstitial cells of Cajal. In the presence of TTX (10−6 M), atropine (10−6M). and l-nitroarginine (10−4 M) human jejunal circular muscle strips contracted phasically (9 cycles/min) and generated slow waves with superimposed spikes. Low concentrations of the KCNH2 blockers E-4031 (10−8 M) and MK-499 (3 × 10−8 M) increased phasic contractile amplitude and the number of spikes per slow wave. The highest concentration of E-4031 (10−6 M) produced a 10–20 mV depolarization, eliminated slow waves, and replaced phasic contractions with a small tonic contracture. E-4031 (10−6 M) did not affect [14C]ACh release from enteric neurons. We conclude that KCNH2 channels play a fundamental role in the control of motility patterns in human jejunum through their ability to modulate the electrical behavior of smooth muscle cells.

Are interstitial cells of Cajal plurifunction cells in the gut?

2008 ◽  
Vol 294 (2) ◽  
pp. G372-G390 ◽  
Author(s):  
Sushil K. Sarna
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Interstitial Cells Of Cajal ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Interstitial Cells ◽  
Slow Waves ◽  
Enteric Neurons ◽  
Motility Disorders ◽  
Cells Of Cajal

The proposed functions of the interstitial cells of Cajal (ICC) are to 1) pace the slow waves and regulate their propagation, 2) mediate enteric neuronal signals to smooth muscle cells, and 3) act as mechanosensors. In addition, impairments of ICC have been implicated in diverse motility disorders. This review critically examines the available evidence for these roles and offers alternate explanations. This review suggests the following: 1) The ICC may not pace the slow waves or help in their propagation. Instead, they may help in maintaining the gradient of resting membrane potential (RMP) through the thickness of the circular muscle layer, which stabilizes the slow waves and enhances their propagation. The impairment of ICC destabilizes the slow waves, resulting in attenuation of their amplitude and impaired propagation. 2) The one-way communication between the enteric neuronal varicosities and the smooth muscle cells occurs by volume transmission, rather than by wired transmission via the ICC. 3) There are fundamental limitations for the ICC to act as mechanosensors. 4) The ICC impair in numerous motility disorders. However, a cause-and-effect relationship between ICC impairment and motility dysfunction is not established. The ICC impair readily and transform to other cell types in response to alterations in their microenvironment, which have limited effects on motility function. Concurrent investigations of the alterations in slow-wave characteristics, excitation-contraction and excitation-inhibition couplings in smooth muscle cells, neurotransmitter synthesis and release in enteric neurons, and the impairment of the ICC are required to understand the etiologies of clinical motility disorders.

Role of gap junctions in structural arrangements of interstitial cells of Cajal and canine ileal smooth muscle

1998 ◽  
Vol 274 (6) ◽  
pp. G1125-G1141 ◽  
Author(s):  
Edwin E. Daniel ◽  
Yu-Fang Wang ◽  
Francisco S. Cayabyab
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Gap Junctions ◽  
Interstitial Cells Of Cajal ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Interstitial Cells ◽  
Slow Waves ◽  
Circular Smooth Muscle ◽  
Cells Of Cajal

We examined the structural and functional basis for pacemaking by interstitial cells of Cajal (ICC) in circular smooth muscle of the canine ileum. Gap junctions were found between ICC of myenteric plexus (MyP), occasionally between MyP ICC and outer circular smooth muscle cells, between individual outer circular smooth muscle cells, between them and ICC of the deep muscular plexus (DMP), and between DMP ICC. No visible gap junctions connected MyP ICC to longitudinal muscle cells or inner circular muscle cells. Occasionally contacts occurred between the two muscle layers. No special structures were found to connect MyP and DMP ICC networks. Octanol concentration dependently reduced the amplitude and frequency of, but did not abolish, slow waves in circular muscle in isolated ileum recorded near the MyP or the DMP. Slow waves triggered from MyP ICC by a current pulse also persisted. Contractile activity was abolished, cells were depolarized, and fast inhibitory junction potentials were reduced by octanol. We conclude that ICC pacemakers of the MyP and DMP utilize gap junctional conductances for pacemaking function but may not require them. Coupling between the two ICC networks may utilize the circular muscle syncytium.

Slow-wave activity in colon: role of network of submucosal interstitial cells of Cajal

1991 ◽  
Vol 260 (4) ◽  
pp. G636-G645 ◽  
Author(s):  
R. Serio ◽  
C. Barajas-Lopez ◽  
E. E. Daniel ◽  
I. Berezin ◽  
J. D. Huizinga
Keyword(s):  
Smooth Muscle ◽  
Slow Wave ◽  
Interstitial Cells Of Cajal ◽  
Circular Muscle ◽  
Interstitial Cells ◽  
Wave Activity ◽  
Slow Waves ◽  
Slow Wave Activity ◽  
Plateau Potentials ◽  
Cells Of Cajal

The present study compares the electrophysiological properties of two preparations dissected from the canine colon circular muscle layer: first, containing the submucosal network of interstitial cells of Cajal (ICC) with two to four associated smooth muscle cell layers, and second, a circular muscle preparation devoid of the submucosal ICC network. In the ICC-rich preparations, consistent slow-wave activity was observed with prolonged plateau potentials of approximately 10-s duration. The plateau potentials were sensitive to D 600. In approximately 45% of circular muscle preparations devoid of the submucosal ICC network (confirmed using electron microscopy) slow waves, of different waveshape, were recorded at frequencies identical to those in whole circular muscle preparations. These slow waves did not show a plateau potential. Compared with ICC-rich preparations with a resting membrane potential of about -80 mV, circular muscle preparations had lower membrane potentials, about -70 mV when active, and about -60 mV when quiescent. Heptanol (1 mM) electrically uncoupled cells, since it abolished electrotonic current spread and allowed measurement of the input resistance by intracellular current injection. Heptanol also affected ionic conductances. Heptanol abolished slow waves; the underlying mechanism needs further investigation. In the presence of heptanol, cells in the isolated ICC network and in circular smooth muscle preparations showed spontaneous hyperpolarizing potential fluctuations at a frequency of four to six per second. These oscillations were abolished by current-induced hyperpolarization and TEA (30 mM) and are therefore likely due to spontaneously active K+ conductance.

Canine colonic circular muscle generates action potentials without the pacemaker component

1994 ◽  
Vol 72 (1) ◽  
pp. 70-81 ◽  
Author(s):  
Louis W. C. Liu ◽  
Jan D. Huizinga
Keyword(s):  
Smooth Muscle ◽  
Calcium Channel ◽  
Action Potentials ◽  
Interstitial Cells Of Cajal ◽  
Longitudinal Muscle ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Interstitial Cells ◽  
Slow Waves ◽  
Cells Of Cajal

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, Ba2+-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. Ba2+-induced oscillations were abolished by 1 μM D600 as well as by repolarization of 6–12 mV. Addition of 0.1 μM 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 μM), 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 Ba2+-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 Ba2+-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.Key words: interstitial cells of Cajal, smooth muscle, dog colon, barium chloride, potassium conductance, Bay K8644, pacemaking activity.

Morphology of the canine pyloric sphincter in relation to function

1989 ◽  
Vol 67 (12) ◽  
pp. 1560-1573 ◽  
Author(s):  
E. E. Daniel ◽  
I. Berezin ◽  
H. D. Allescher ◽  
H. Manaka ◽  
V. Posey-Daniel
Keyword(s):  
Smooth Muscle ◽  
Substance P ◽  
Smooth Muscle Cells ◽  
Gap Junctions ◽  
Vasoactive Intestinal Polypeptide ◽  
Interstitial Cells Of Cajal ◽  
Circular Muscle ◽  
Interstitial Cells ◽  
Pyloric Sphincter ◽  
Cells Of Cajal

The ultrastructure and immunocytochemistry of the canine distal pyloric muscle loop, the pyloric sphincter, were studied. Cells in this muscle were connected by gap junctions, fewer than in the antrum or corpus. The sphincter had a dense innervation and a sparse population of interstitial cells of Cajal. Most such cells were of the circular muscle type but a few were of the type in the myenteric plexus. Nerves were sometimes associated with interstitial cell profiles, but most nerves were neither close to nor associated with interstitial cells nor close to smooth muscle cells. Nerve profiles were characterized by an unusually high proportion of varicosities with a majority or a high proportion of large granular vesicles. Many of these were shown to contain material immunoreactive for vasoactive intestinal polypeptide (VIP) and some had substance P (SP) immunoreactive material. All were presumed to be peptidergic. VIP was present in a higher concentration in this muscle than in adjacent antral or duodenal circular muscle. Interstitial cells of Cajal made gap junctions to smooth muscle and to one another and might provide myogenic pacemaking activity for this muscle, but there was no evidence of a close or special relationship between nerves with VIP or SP and these cells. The absence of close relationships between nerves and either interstitial cells or smooth muscle cells leaves unanswered questions about the structural basis for previous observations of discrete excitatory responses or pyloric sphincter to single stimuli or nerves up to one per second. In conclusion, the structural observations suggest that this muscle has special neural and myogenic control systems and that interstitial cells may function to control myogenic activity of this muscle but not to mediate neural signals.Key words: vasoactive intestinal polypeptide, interstitial cells of Cajal, neuropeptides, gap junctions, substance P.

Neuromuscular structures in opossum esophagus: role of interstitial cells of Cajal

1984 ◽  
Vol 246 (3) ◽  
pp. G305-G315 ◽  
Author(s):  
E. E. Daniel ◽  
V. Posey-Daniel
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Interstitial Cells Of Cajal ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Interstitial Cells ◽  
Complete Relaxation ◽  
Granular Vesicles ◽  
Cells Of Cajal

The structures of the lower esophageal sphincter (LES) and body circular muscle (BCM) from opossum were compared as to neural and muscular structures and the structural relations of interstitial cells of Cajal to nerves and muscle cells. Both LES and BCM were densely innervated by nerves with varicosities containing many small agranular vesicles and a few large granular vesicles. These nerves were more closely related structurally to the interstitial cells of Cajal than to smooth muscle cells. More gap junctions were observed between smooth muscle cells and between interstitial cells of Cajal and smooth muscle cells in BCM than in LES. Those between smooth muscle cells were larger in BCM. Complete relaxation of the LES strip by isoproterenol reduced these differences but did not eliminate them. The finding that interstitial cells of Cajal often had gap-junction contacts to smooth muscle and close associations with nerves is consistent with the hypothesis that interstitial cells are intercalated between the nerves and muscles and may mediate nerve responses. These findings also suggest that LES muscle cells may be less well coupled electrically than BCM muscle cells.

Proteins of interstitial cells of Cajal and intestinal smooth muscle, colocalized with caveolin-1

2005 ◽  
Vol 288 (3) ◽  
pp. G571-G585 ◽  
Author(s):  
Woo Jung Cho ◽  
E. E. Daniel
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Gap Junction ◽  
Interstitial Cells Of Cajal ◽  
Smooth Muscles ◽  
Circular Muscle ◽  
Interstitial Cells ◽  
Caveolin 1 ◽  
Cells Of Cajal ◽  
Junction Proteins

The murine jejunum and lower esophageal sphincter (LES) were examined to determine the locations of various signaling molecules and their colocalization with caveolin-1 and one another. Caveolin-1 was present in punctate sites of the plasma membranes (PM) of all smooth muscles and diffusely in all classes of interstitial cells of Cajal (ICC; identified by c-kit immunoreactivity), ICC-myenteric plexus (MP), ICC-deep muscular plexus (DMP), ICC-serosa (ICC-S), and ICC-intramuscularis (IM). In general, all ICC also contained the L-type Ca2+ (L-Ca2+) channel, the PM Ca2+ pump, and the Na+/Ca2+ exchanger-1 localized with caveolin-1. ICC in various sites also contained Ca2+-sequestering molecules such as calreticulin and calsequestrin. Calreticulin was present also in smooth muscle, frequently in the cytosol, whereas calsequestrin was present in skeletal muscle of the esophagus. Gap junction proteins connexin-43 and -40 were present in circular muscle of jejunum but not in longitudinal muscle or in LES. In some cases, these proteins were associated with ICC-DMP. The large-conductance Ca2+-activated K+ channel was present in smooth muscle and skeletal muscle of esophagus and some ICC but was not colocalized with caveolin-1. These findings suggest that all ICC have several Ca2+-handling and -sequestering molecules, although the functions of only the L-Ca2+ channel are currently known. They also suggest that gap junction proteins are located at sites where ultrastructural gap junctions are know to exist in circular muscle of intestine but not in other smooth muscles. These findings also point to the need to evaluate the function of Ca2+ sequestration in ICC.

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

1994 ◽  
Vol 266 (3) ◽  
pp. G485-G496 ◽  
Author(s):  
L. W. Liu ◽  
L. Thuneberg ◽  
J. D. Huizinga
Keyword(s):  
Methylene Blue ◽  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Electrical Activity ◽  
Slow Wave ◽  
Interstitial Cells Of Cajal ◽  
Wave Activity ◽  
Slow Waves ◽  
Slow Wave Activity ◽  
Cells Of Cajal

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.

Pacemaker potentials generated by interstitial cells of Cajal in the murine intestine

2005 ◽  
Vol 288 (3) ◽  
pp. C710-C720 ◽  
Author(s):  
Yoshihiko Kito ◽  
Sean M. Ward ◽  
Kenton M. Sanders
Keyword(s):  
Interstitial Cells Of Cajal ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Interstitial Cells ◽  
Slow Waves ◽  
Pacemaker Activity ◽  
Dependent Manner ◽  
Plateau Potential ◽  
Pacemaker Potentials ◽  
Cells Of Cajal

Pacemaker potentials were recorded in situ from myenteric interstitial cells of Cajal (ICC-MY) in the murine small intestine. The nature of the two components of pacemaker potentials (upstroke and plateau) were investigated and compared with slow waves recorded from circular muscle cells. Pacemaker potentials and slow waves were not blocked by nifedipine (3 μM). In the presence of nifedipine, mibefradil, a voltage-dependent Ca2+ channel blocker, reduced the amplitude, frequency, and rate of rise of upstroke depolarization (d V/d tmax) of pacemaker potentials and slow waves in a dose-dependent manner (1–30 μM). Mibefradil (30 μM) changed the pattern of pacemaker potentials from rapidly rising, high-frequency events to slowly depolarizing, low-frequency events with considerable membrane noise (unitary potentials) between pacemaker potentials. Caffeine (3 mM) abolished pacemaker potentials in the presence of mibefradil. Pinacidil (10 μM), an ATP-sensitive K+ channel opener, hyperpolarized ICC-MY and increased the amplitude and d V/d tmax without affecting frequency. Pinacidil hyperpolarized smooth muscle cells and attenuated the amplitude and d V/d tmax of slow waves without affecting frequency. The effects of pinacidil were blocked by glibenclamide (10 μM). These data suggest that slow waves are electrotonic potentials driven by pacemaker potentials. The upstroke component of pacemaker potentials is due to activation of dihydropyridine-resistant Ca2+ channels, and this depolarization entrains pacemaker activity to create the plateau potential. The plateau potential may be due to summation of unitary potentials generated by individual or small groups of pacemaker units in ICC-MY. Entrainment of unitary potentials appears to depend on Ca2+ entry during upstroke depolarization.

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