Biomedical subjects

J D Huizinga

Publications and source records attributed to J D Huizinga.

At least 73 records · Page 4Linked to original sources

PubMed1993

Immunohistochemical localization of a gap junction protein (connexin43) in the muscularis externa of murine, canine, and human intestine.

Electron-microscopic studies have revealed a heterogeneous distribution of gap junctions in the muscularis externa of mammalian intestines. This heterogeneity is observed at four different levels: among species; between small and large intestines; between longitudinal and circular muscle layers; and between subdivisions of the circular muscle layer. We correlated results obtained with two immunomethods, using an antibody to the known gap-junctional protein (connexin43) with ultrastructural findings, and further evaluated the respective sensitivity of these two approaches. For comparative reasons we also included the vascular smooth muscle of coronary arteries into our study. Two versions of the immunotechnique (peroxidase-antiperoxidase and fluorescence methods) were applied to frozen sections of murine, canine, and human small and large intestines, as well as to pig coronary artery. In the small intestine of all three species a very strong reactivity marked the outer main division of the circular muscle layer, while the longitudinal muscle layer as well as the inner thin division of the circular muscle layer were negative. In murine and human colon both muscle layers were negative, while in canine colon the border layer between the circular muscle and the submucosa reacted strongly, and scattered activity was found in the portion of the circular muscle layer (one tenth of its thickness) closest to the submucosa. The remainder of the circular muscle layer and the entire longitudinal muscle layer were negative in the canine colon. In the coronary artery we could not confirm the positive, specific labeling reported by other investigators (l.c.).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Altered small intestinal smooth muscle function in Crohn's disease.

BACKGROUND: Studies in animals indicate that inflammation causes changes in smooth muscle contractility. Because Crohn's disease is associated with altered motility, this study investigated the contractility of intestinal muscle resected from patients with or without Crohn's disease. METHODS: The isometric contraction of muscle strips from the small bowel of 36 patients with and 24 patients without Crohn's disease was examined. RESULTS: In longitudinal muscle from patients with Crohn's disease, there was a 55% increase in maximum contraction induced by carbachol but not histamine, but there was no change in the 50% effective dose (ED50) for these agonists. In contrast, in circular muscle from patients with Crohn's disease there was a sevenfold decrease in the ED50 value for carbachol but no change in maximum contraction. There was a 2.5-fold increase in the maximum response to histamine, but no change in ED50, in circular muscle from patients with Crohn's disease. However, there was no change in KCl-induced contraction between the two groups. The carbachol responses were atropine sensitive. Histamine responses were blocked by the H1 antagonist mepyramine but were not altered by a diamine oxidase inhibitor. All responses were tetrodotoxin insensitive. CONCLUSION: These results show altered receptor-mediated contraction in small intestinal muscle in patients with Crohn's disease.

Adolescent↗

PubMed1993

New transmitters and new targets in the autonomic nervous system.

Several recent findings have made research into the autonomic nervous system even more exciting, such as the revelation that nitric oxide is a major neurotransmitter, the delineation of the physiological roles for purines and vasoactive intestinal peptide, and the discovery that the interstitial cells of Cajal are major target cells for enteric innervation. Nitric oxide is probably the major neurotransmitter evoking inhibitory junction potentials in smooth muscle. ATP is a mediator of non-adrenergic non-cholinergic enteric innervation, as well as being a fast neurotransmitter in peripheral and autonomic neuro-neuronal synapses. The interactions between enteric nerves and both immune cells and interstitial cells of Cajal (as pacemaker cells of gut smooth muscle) are forcing a rethink of many aspects of gut physiology.

Animals↗

PubMed1993

Characterization of the outward rectifying potassium channel in a novel mouse intestinal smooth muscle cell preparation.

1. The outward rectifying K+ conductance and underlying single channel behaviour in mouse small intestine (MSI) smooth muscle cells was studied using microelectrode impalement and the patch clamp technique. 2. At 37 degrees C, smooth muscle cells in MSI explants had a resting membrane potential around -65 mV and showed spontaneous electrical and mechanical activity. 3. Under whole-cell voltage clamp, depolarization of smooth muscle cells in the explants evoked a methoxyverapamil (D600)-sensitive, partially inactivating inward current and a non-inactivating outward current. The outward current was also observed in enzymatically dispersed cells from neonatal mouse small intestine. 4. The reversal potential of the outward current as established in tail current experiments was -70.2 mV. Tail currents could be fitted with a single exponential, suggesting the participation of only one population of channels. 5. The outward current was sensitive to 4-aminopyridine (10(-4) M), Ba2+ (1 mM) and to the presence of Cs+ in the pipette, but not to D600 (10(-6) M), or the presence of ATP (1 mM) in the pipette. 6. In the cell-attached patch configuration, a unitary outward current was observed that showed increased activity upon depolarization of the patch. The current-voltage relationship was close to linear with a slope conductance of 186 pS. 7. With normal K+ (6 mM) in the pipette, the extrapolated reversal potential for the unitary current was around -75 mV, while with high K+ (120 mM) the reversal potential was close to 0 mV. 8. Averaging single channel traces recorded under a depolarizing pulse protocol resulted in a trace with similar time characteristics as the outward current observed in the whole-cell configuration. 9. The burst behaviour of the channel was described by a simple model consisting of two closed states, Cf (intraburst closed state) and Cs (interburst closed state) and an open state (O). The rate constants in the model showed differential sensitivity to potential changes, channel blockade by Ba2+ and equimolar K+ conditions. 10. It was concluded that the outward rectifying potassium current in MSI smooth muscle cells is mediated by a 186 pS bursting channel. Voltage dependency and Ba2+ blockade are mainly reflected by changes in the transition rate from the open channel state to the interburst closed state.

4-Aminopyridine↗

PubMed1993

Electrical coupling of circular muscle to longitudinal muscle and interstitial cells of Cajal in canine colon.

1. Electrical communication between circular muscle, longitudinal muscle and interstitial cells of Cajal (ICC) was investigated; the hypothesis was tested that the resting membrane potential (RMP) gradient in the circular muscle of canine colon is caused by electrical coupling to neighbouring cells. 2. Isolated longitudinal muscle exhibited spike-like action potentials at a RMP of -45 mV with a frequency and amplitude of 20 cycles/min and 12 mV, respectively. 3. The circular muscle (CM), devoid of longitudinal muscle, myenteric plexus and submuscular ICC-smooth-muscle network, was electrically quiescent at a uniform RMP of -62 mV across the entire circular muscle layer. 4. Preparations consisting of only the submuscular ICC network and a few adjacent layers of circular muscle cells exhibited slow wave-type action potentials at a RMP of about -80 mV. 5. In ICC-CM preparations, consisting of the submuscular ICC network and circular muscle, a RMP gradient of 10 mV was observed near the submucosal border, whereas the RMP was constant at -62 mV in the myenteric half of the circular muscle. 6. In full thickness (FT) preparations, a RMP gradient of 23 mV was observed. The RMP decreased gradually from -71 mV at the submucosal border to -48 mV at the myenteric border of the circular muscle. 7. Coupling of longitudinal muscle to circular muscle caused circular muscle cells at the myenteric surface to depolarize by 14 mV and longitudinal muscle cells to hyperpolarize by 3 mV. 8. In the ICC-CM preparations, the slow wave amplitudes did not decay exponentially away from the ICC network indicating that slow waves propagated actively into the circular muscle; in the FT preparations there was an apparent exponential decay but this was due to the RMP gradient. 9. Spike-like action potentials (SLAPs) superimposed on the plateau phase of slow waves did not decay exponentially away from the myenteric border suggesting that SLAPs were generated within the circular muscle layer. 10. In summary, circular muscle cells possess a uniform intrinsic RMP of -62 mV. The RMP gradient in situ is caused by electrical coupling of circular muscle cells to longitudinal muscle cells and the submuscular network of ICC. In situ, slow wave-type action potentials propagate actively into the circular muscle layer, and, dependent on the level of excitation, circular muscle cells actively generate spikes.

Action Potentials↗

PubMed1993

Selective accumulation of methylene blue by interstitial cells of Cajal in canine colon.

The network of interstitial cells of Cajal (ICC) at the submucosal surface of the canine colon was selectively stained by incubation with 15-50 microM methylene blue for 30-45 min. The network was composed of regularly scattered ICC cell bodies interconnected by long processes. Circular muscle cells were unstained. Staining of neurons was limited to one or two axons within bundles. The ICC network had a thickness of a single cell, since no overlapping of ICC cell bodies was observed. The ICC network connected the circular muscle cells at the submucosal surface across the septa which circumferentially divided the circular muscle into lamellae. Methylene blue at 50 microM slightly decreased the resting membrane potential and increased the duration of slow waves, leading to an increase in the force of phasic contractions, with no significant influence on other slow-wave parameters. Methylene blue produced neither electrophysiological nor mechanical effects on circular muscle preparations from which the submuscular ICC network was removed, indicating that the excitatory effects of methylene blue on the full-thickness circular muscle layer were mediated by ICC. In summary, the three-dimensional aspects of the submuscular ICC network can be visualized after selective staining by methylene blue. This staining does not affect physiological characteristics of smooth muscle cells.

Animals↗

PubMed1992

Intercellular communication in smooth muscle.

The functioning of a group of cells as a tissue depends on intercellular communication; an example is the spread of action potentials through intestinal tissue resulting in synchronized contraction. Recent evidence for cell heterogeneity within smooth muscle tissues has renewed research into cell coupling. Electrical coupling is essential for propagation of action potentials in gastrointestinal smooth muscle. Metabolic coupling may be involved in generation of pacemaker activity. This review deals with the role of cell coupling in tissue function and some of the issues discussed are the relationship between electrical synchronization and gap junctions, metabolic coupling, and the role of interstitial cells of Cajal in coupling.

Animals↗

PubMed1992

Ouabain-induced excitation of colonic smooth muscle due to block of K+ conductance by intracellular Na+ ions.

The mechanism by which ouabain causes excitation of canine colonic circular smooth muscle was investigated. Ouabain-induced depolarization and increase in contractility were related to the concentration of extracellular sodium and prevented by complete substitution of sodium ions with N-methyl-D-glucamine or lithium ions. Absence of external sodium ions did not prevent the depolarization and increase in contractility induced by tetraethylammonium. Exposure of the muscle strips to sodium-free solutions produced a transient hyperpolarization and decrease in the input membrane resistance consistent with the hypothesis that intracellular sodium blocks potassium conductance. The relationship between the membrane potential and the extracellular potassium concentration indicated that the resting membrane potential is mainly determined by the membrane potassium conductance. Our data suggest the following mechanism of action for ouabain: (a) ouabain blocks Na+/K+ pump thereby increasing the intracellular sodium concentration; (b) increase in intracellular sodium inhibits membrane potassium conductance, which depolarizes the membrane and prolongs the slow wave plateau, resulting in an increase of the force of contraction. The direct contribution of the sodium pump to the resting membrane potential, if any, can only be minor (< 6 mV).

Animals↗

PubMed1992

On the pharmacological and physiological role of glibenclamide-sensitive potassium channels in colonic smooth muscle.

Actions of activators of glibenclamide sensitive K+ channels on canine colonic circular muscle were investigated. Cromakalim as well as its (-) enantiomer lemakalim caused inhibition of spontaneous phasic contractile activity (EC50's 4.4 +/- 0.1 x 10(-7) M and 2.3 +/- 0.4 x 10(-7) M, respectively) and of carbachol induced activity (EC50's: 9.4 +/- 5.1 x 10(-7) M and 4.3 +/- 1.4 x 10(-7) M, respectively). Cromakalim and lemakalim effects were completely inhibited by glibenclamide. Additive effects between K+ channel activators and other drugs relaxing colonic muscle (the L-type calcium channel blocker D600 and forskolin) were seen. A physiological role for specific glibenclamide sensitive K+ channels, if existing, remains unresolved. The present study indicates that the non-adrenergic inhibitory nerves do not act through these channels, neither does stimulation of muscarinic or beta-adrenergic receptors.

Animals↗

PubMed1992

Mast cell ionic channels: significance for stimulus-secretion coupling.

The activation of mast cells (MC) due to immunological stimulation causes an immediate and dramatic inflammatory response. We review current evidence indicating that the membrane permeabilities for calcium, chloride, sodium, and potassium have a significant role in the activation of these cells, and in some cases, specific ionic channels have been identified. Moreover, a number of intracellular mechanisms controlling these channels are pointed out, including different classes of G proteins, intracellular calcium, cAMP, and products of phosphoinositol breakdown. However, the interplay between factors controlling membrane conductances for different ions is not currently understood. The diversity of ionic effects on MC activation is depicted, illustrating that the ionic mechanisms of MC activation are specific for different MC types. Since nerve/mast cell interaction is a key element in the burgeoning field of neuroimmunology, we discuss the role of ionic channels as targets of neurotransmitter action in MC activation.

Animals↗

PubMed1992

Excitability of canine colon circular muscle disconnected from the network of interstitial cells of Cajal.

The 6 cpm omnipresent slow waves recorded in the circular muscle (CM) layer of canine colon are generated at the submucosal surface of the CM layer. After removal of the submucosal network of interstitial cells of Cajal (ICC), 66% of the CM preparations (25 of 38) were quiescent in Krebs solution. In the presence of carbachol, seven of nine of these spontaneously quiescent CM preparations demonstrated slow wave-like activity with mean frequency, duration and amplitude of 5.9 +/- 0.4 cpm, 2.8 +/- 0.5 s, and 0.8 +/- 0.2 mV, respectively. Similar slow wave-like activities were induced by TEA (seven out of eight quiescent CM preparations) with frequency, duration and amplitude of 6.1 +/- 0.2 cpm, 2.7 +/- 0.5 s, and 1.0 +/- 0.2 mV, respectively, and by BaCl2 (eight of eight quiescent CM preparations) with frequency, duration, and amplitude of 6.3 +/- 0.3 cpm, 1.8 +/- 0.2 s, and 0.5 +/- 0.1 mV, respectively. All the induced activities were abolished in the presence of 1 microM D600. CM preparations with the submucosal ICC network intact (ICC-CM) showed slow wave activity in Krebs solution at a frequency of 6.2 +/- 0.2 cpm, a duration of 3.6 +/- 0.2 s, and an amplitude of 1.0 +/- 0.1 mV (n = 22). When ICC-CM preparations were stimulated by BaCl2, carbachol, or TEA, the slow wave frequency did not change significantly, but the duration increased as well as the amplitude. In the presence of D600, the upstroke of slow waves remained and the frequency was not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Involvement of nitric oxide in nerve-mediated inhibition and action of vasoactive intestinal peptide in colonic smooth muscle.

Neurally mediated relaxation of canine colonic smooth muscle is associated with an increase in the resting membrane potential and is blocked by inhibition of nitric oxide synthesis. N omega-nitro-L-arginine completely prevented nerve-mediated relaxation, an effect that was reversed by L-arginine but not D-arginine. Vasoactive intestinal peptide (VIP) also relaxed canine colonic smooth muscle. Part of this relaxation was due to activation of inhibitory nerves and this effect was mediated by nitric oxide. In addition to the neurally mediated effect, VIP affected smooth muscle directly. This relaxation was associated with a reduction of the plateau phase of the slow-wave type action potential, without an effect on the resting membrane potential. This action of VIP was similar to that of forskolin which suggests that VIP increases intracellular cyclic AMP. In summary, nitric oxide mediates inhibitory innervation to smooth muscle as well as activation of inhibitory nerves by VIP. The electrophysiological mechanism by which VIP directly affects smooth muscle is described, an effect not mediated by nitric oxide.

Animals↗

PubMed1991

Generation of slow-wave-type action potentials in canine colon smooth muscle involves a non-L-type Ca2+ conductance.

1. The hypothesis was addressed that a non-L-type calcium conductance is involved in the generation of the initial part of the slow-wave-type action potential in the canine colon. 2. In the absence of a sodium and chloride gradient (NaCl replaced by glucamine), and in the presence of nitrendipine (in 'glucamine-nitrendipine' Krebs solution), a major portion of the upstroke potential of the slow wave persists at unchanged frequency. 3. In 'glucamine-nitrendipine' Krebs solution, the rate of rise and amplitude of the upstroke potential is reduced by removal of extracellular calcium in a concentration-dependent manner. 4. The rate of rise and the amplitude of the upstroke potential is in a concentration-dependent manner reduced by Ni2+ greater than Cd2+ greater than Co2+ greater than Mg2+. 5. In 'glucamine-nitrendipine' Krebs solution, Ba2+ cannot replace Ca2+ in the generation of the upstroke potential. 6. Positive evidence was obtained for the hypothesis that a non-L-type calcium conductance is involved in the initiation of the slow-wave-type action potential in colonic smooth muscle.

Action Potentials↗

PubMed1991

Effect of voltage and cyclic AMP on frequency of slow-wave-type action potentials in canine colon smooth muscle.

1. A non-L-type calcium conductance is involved in the generation of the initial part of the slow-wave-type action potential in colonic smooth muscle. The present study addresses the question whether this conductance is voltage or metabolically activated. 2. Current-induced hyperpolarization increased frequency and amplitude of slow waves measured in Krebs solution. 3. The upstroke potential was 'isolated' from the slow wave by superfusion with 'glucamine-nitrendipine' Krebs solution (NaCl was replaced by glucamine, nitrendipine was added). 4. Hyperpolarization up to -100 mV did not affect the upstroke potential frequency and increased its amplitude. Only hyperpolarization further than -100 mV decreased the frequency less than or equal to 20%, and reduced the amplitude less than or equal to 20%. 5. Depolarization did not affect the upstroke potential frequency. 6. Forskolin, but not 1,9-dideoxyforskolin dramatically decreased the upstroke potential frequency, without affecting other parameters including the resting membrane potential. 7. The effect of forskolin was mimicked by dibutyryl cyclic AMP, 8-bromo-cyclic AMP and 3-isobutyl-1-methylxanthine (IBMX), but not extracellular cyclic AMP. 8. The upstroke potential could not be evoked by depolarizing pulses after inhibition of activity by forskolin. 9. The effect of forskolin could be reversed by the calcium ionophore A23187. 10. In summary, voltage changes up to -40 mV and down to -100 mV do not, but changes in intracellular cyclic AMP do affect the frequency of the upstroke potential. 11. It is likely that intracellular metabolic activity, which may include cyclic AMP but not a voltage change, activates the conductance responsible for the generation of the upstroke potential.

Action Potentials↗

PubMed1991

Action potentials in gastrointestinal smooth muscle.

Recent investigation of the ultrastructure and electrophysiology of gastrointestinal smooth muscle layers has revealed a fascinating heterogeneity in cell type, cell structure, intercellular communication, and generated electrical activities. Networks of interstitial cells of Cajal (ICC) have been identified in many muscle layers and evidence is accumulating for a role of these networks in gut pacemaking activity. Synchronized motility in the organs of the gut result from interaction between ICC, neural-tissue, and smooth muscle cells. Regulation of cell to cell communication between the different cell types will be an important area for further research. Progress has been made in the elucidation of the ionic basis of the slow wave type action potentials and the spike-like action potentials. The mechanism underlying smooth muscle autorhythmicity seems different from that encountered in cardiac tissue, and evidence exists for metabolic regulation of the frequency of slow wave type action potentials.

Action Potentials↗

PubMed1991

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

Alcohols↗

PubMed1991

Potassium channel activation by cromakalim affects the slow wave type action potential of colonic smooth muscle.

The objective was to determine the existence of a glybenclamide-sensitive K+ conductance in intestinal smooth muscle, to study a possible role for this conductance in the generation of colonic slow wave type action potentials and to investigate if modification of this conductance could alter the action potentials and hence colonic motility. Intracellular electrical recording techniques were used to study properties of cells from the network of smooth muscle cells and interstitial cells of Cajal at the submucosal border of the circular muscle layer of the canine colon, where colonic pacemaker activity is generated. Cromakalim, dose dependently, hyperpolarized the cells and decreased the duration of the action potential, thereby inhibiting contractile activity. The upstroke amplitude and the action potential frequency remained unaltered. Glybenclamide did not affect any parameter of spontaneous electrical activity but prevented all effects of cromakalim. Cromakalim seems to act through increase in K+ conductance because the cromakalim-induced hyperpolarization is accompanied by a marked reduction in input resistance, is inhibited by glybenclamide and tetraethylammonium and it is shown that the cromakalim effect does not occur through effects on Na+ or Cl- conductances. Thus, glybenclamide-sensitive K+ conductance exists in colonic smooth muscle; the spontaneous development of slow wave type action potentials in this tissue occurs independent of this conductance. Its existence may provide pharmacological possibilities to affect gastrointestinal motility.

Action Potentials↗

PubMed1990

Jejunal circular muscle motility is decreased in nematode-infected rat.

Jejunal circular muscle motility was studied in vitro in rats 8-10 days after inoculation with the inflammation-inducing nematode Nippostrongylus brasiliensis. The passive properties of the muscle, i.e., the development of passive tension and the optimal amount of stretch for active contractions, were unchanged by infection. Infection decreased the development of active resting tension, spontaneous contractions, muscle contraction to muscarinic receptor activation, and direct electrical stimulation. Relaxation to beta-adrenergic stimulation was also decreased in tissues from infected animals. Response to cholinergic stimulation, spontaneous contractions, and active resting tension were completely dependent on extracellular calcium. The dominant response to electrical stimulation of intrinsic nerves was relaxation in control tissue and contraction in tissue from infected rats. In the presence of atropine, all tissues from control rats but only 33% of the tissues from infected rats relaxed, suggesting a marked difference in functional inhibitory innervation. The inflammation may have either decreased the circular muscle responsiveness to the inhibitory transmitter or decreased the release of this transmitter. Thus, a nematode infection produces decreased responsiveness of the intestinal circular muscle to both contracting and relaxing stimuli and causes a reduction in functional inhibitory innervation in this layer. These changes suggest mechanisms for the reduction of intestinal transit observed after some nematode infections.

Animals↗