Electrical coupling in the circular muscles of dog jejunum

1979 ◽  
Vol 57 (6) ◽  
pp. 578-580 ◽  
Author(s):  
Elane Zelcer ◽  
E. E. Daniel
Keyword(s):  
Gap Junctions ◽  
Electrical Coupling ◽  
Circular Muscle ◽  
Muscle Layer ◽  
Dense Layer ◽  
Isolated Cells ◽  
Alternate Pathway ◽  
Significant Difference ◽  
Circular Layer ◽  
Passive Current

Two distinct layers of circular muscle have previously been demonstrated in dog jejunum, the main circular layer containing many gap junction contacts, and an inner dense muscle layer where no gap junctions have been found. Length constants were determined for these muscle layers and no significant difference was found between these values. The main circular muscle cells had lower membrane potentials and may have had abnormally low space constants owing to injury. It was concluded that the absence of gap junctions in the inner dense layer does not reduce the spread of passive current as might be expected of electrically isolated cells, and it is suggested that an alternate pathway for passive current exists in this layer.

Correlation between electrical and morphological properties of canine pyloric circular muscle

1991 ◽  
Vol 260 (3) ◽  
pp. G390-G398 ◽  
Author(s):  
F. Vogalis ◽  
S. M. Ward ◽  
K. M. Sanders
Keyword(s):  
Single Cells ◽  
Electrical Coupling ◽  
Circular Muscle ◽  
Muscle Layer ◽  
Morphological Properties ◽  
Morphological Examination ◽  
Isolated Cells ◽  
Time Constants ◽  
Morphological Studies ◽  
Cable Properties

Electrical slow waves decay in amplitude as they conduct from the myenteric to the submucosal regions of the circular muscle layer in the canine pyloric sphincter. We used the partitioned chamber method to study the passive and active properties of pyloric muscles, and we found that length constants of circular muscles of myenteric region were significantly longer than muscles near the submucosal surface. These data suggested differences in either membrane resistance, junctional resistance, or cytoplasmic resistance. The first parameter was evaluated by measuring time constants in intact tissues and single cells isolated from the submucosal and myenteric regions. Membrane time constants were not different in the two regions, nor were differences found in the input resistances of isolated cells. Morphological studies failed to demonstrate differences in cell diameters in the two regions suggesting that cytoplasmic resistances are similar. These findings suggest that the different cable properties in the two regions may be due to differences in electrical coupling. Morphological examination revealed similar numbers of gap junctions between cells in the two regions, but large differences were noted in the size of muscular bundles. Muscles of the myenteric region were arranged into large, tightly packed bundles, whereas muscles of the submucosal region consisted of small bundles with an extensive extracellular space filled with connective tissue. We suggest that the difference in cable properties may be due to differences in electrical coupling between bundles. These data suggest that submucosal muscles function more like a multiunit smooth muscle, whereas myenteric muscles behave as a single unit.

Electrical coupling in rat myometrium during pregnancy

1979 ◽  
Vol 57 (5) ◽  
pp. 490-495 ◽  
Author(s):  
Elane Zelcer ◽  
E. E. Daniel
Keyword(s):  
Gap Junctions ◽  
Electrical Coupling ◽  
Longitudinal Axis ◽  
Significant Difference ◽  
Near Term ◽  
Passive Current

Gap junctions were found in rat myometrium only during parturition or abortion. A comparison was made between the values of the length constants obtained from longitudinally cut strips of rat myometrium at the midterm stage of pregnancy and during parturition. No significant difference was found between these values. No significant difference was found between length constants measured in myometrium from rats near term (22 days) and those during parturition, or between midterm myometrium and myometrium taken from animals aborting at midterm following ovariectomy. It was concluded that the appearance of gap junctions in parturient myometrium does not alter the spread of passive current in the longitudinal axis of the cells in these tissues. It is suggested that gap junctions are not required for spread of passive current, and that other structures may provide an alternate path.

Pacemaker activity in septal structures of canine colonic circular muscle

1990 ◽  
Vol 259 (2) ◽  
pp. G264-G273 ◽  
Author(s):  
S. M. Ward ◽  
K. M. Sanders
Keyword(s):  
Slow Wave ◽  
Electrical Coupling ◽  
Circular Muscle ◽  
Proximal Colon ◽  
Slow Waves ◽  
Pacemaker Activity ◽  
Electrical Measurements ◽  
Morphological Studies ◽  
Circular Layer ◽  
And Function

Morphological and electrophysiological experiments were performed to characterize the pacemaker areas of the circular muscle in the canine proximal colon. Morphological studies showed interstitial cells of Cajal lining the submucosal surface of the circular layer and the septal structures that separate the circular layer into bundles. Electrical measurements suggested that slow waves may propagate into the thickness of the circular muscle in a regenerative manner along the surface of these septa. Removal of the submucosal pacemaker region blocked generation of slow waves in nonseptal regions of the circular muscle, but slow-wave activity continued in the circular muscle near septa. These data suggest that slow-wave pacemaker activity is not limited to a two-dimensional surface at the submucosal surface but extends into the interior of the circular layer along septal invaginations. Experiments were also performed to determine the dominance of pacemaker activity (i.e., septal vs. submucosal), and examples were found in which both areas appeared to initiate slow waves in intact muscles. Other studies showed that slow waves could propagate across septa, suggesting some form of electrical coupling between circular muscle bundles. This study provides a more complete view of the structure and function of pacemaker areas in the canine proximal colon.

Cholinergic nerve-mediated excitation in the guinea pig choledochoduodenal junction activated by distension

1994 ◽  
Vol 267 (5) ◽  
pp. G938-G946 ◽  
Author(s):  
F. Vogalis ◽  
R. R. Bywater ◽  
G. S. Taylor
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Action Potential ◽  
Action Potentials ◽  
Discharge Rate ◽  
Circular Muscle ◽  
Muscle Layer ◽  
Circular Muscle Layer ◽  
Circular Layer ◽  
Longitudinal Layer

The electrical basis of propulsive contractions in the guinea pig choledochoduodenal junction (CDJ), which are triggered by distension, was investigated using intracellular microelectrode recording techniques. The isolated CDJ was placed in a continuously perfused tissue chamber at 37 degrees C. Membrane potential was recorded from smooth muscle cells in either the ampulla or in the upper CDJ (upper junction) regions, which were immobilized by pinning. Distension of the upper junction (20-30 s) by increasing intraductal hydrostatic pressure (mean elevation: 2.0 +/- 0.3 kPa, n = 13) triggered "transient depolarizations" (TDs: < 5 mV in amplitude and 2-5 s in duration) and action potentials in the circular muscle layer of the ampulla. The frequency of TDs in the ampulla was increased from 2.2 +/- 0.2 to 15.9 +/- 2.2 min-1 (n = 13) during distension. Simultaneous impalements of cells in the longitudinal and circular muscle layers in the ampulla revealed that subthreshold TDs in the circular layer were associated with an increased rate of action potential discharge in the longitudinal layer. Atropine (Atr; 1.4 x 10(-6) M) and tetrodotoxin (TTX; 3.1 x 10(-6) M blocked the distension-evoked increase in TD frequency, without affecting the frequency of ongoing TDs. The sulfated octapeptide of cholecystokinin (1-5 x 10(-8) M) increased the amplitude of TDs recorded in the circular muscle layer of the ampulla and increased action potential discharge rate. In separate recordings, radial stretch of the ampulla region increased the rate of discharge of action potentials in the smooth muscle of the upper junction.(ABSTRACT TRUNCATED AT 250 WORDS)

Excitatory and inhibitory neural regulation of canine pyloric smooth muscle

1990 ◽  
Vol 259 (1) ◽  
pp. G125-G133 ◽  
Author(s):  
F. Vogalis ◽  
K. M. Sanders
Keyword(s):  
Action Potentials ◽  
Slow Component ◽  
Circular Muscle ◽  
Muscle Layer ◽  
Slow Waves ◽  
Cross Sectional ◽  
Intrinsic Innervation ◽  
Circular Layer ◽  
Neuromuscular Apparatus ◽  
Excitatory Junction Potentials

Studies were performed to characterize the intrinsic innervation of the circular muscle layer of the canine pylorus. Cross-sectional strips of muscle were studied with intracellular recording techniques, and junction potentials were elicited with transmural nerve stimulation. Neurally mediated responses were recorded from cells at several points through the thickness of the circular layer. Excitatory junction potentials (EJPs) increased and inhibitory junction potentials (IJPs) decreased in amplitude with distance from the myenteric border of the circular muscle. Atropine blocked EJPs throughout the circular layer, demonstrating that excitatory inputs are primarily cholinergic. The gradient in IJP amplitude persisted after blockade of EJPs. Three components of IJPs were identified: 1) a fast, apamin-sensitive component that reached a peak and decayed within approximately 1 s; 2) a slower, apamin-insensitive component that reached a peak within 800 ms but decayed slowly over 5 s; and 3) a very slow component that reached a maximum in 7-10 s. Junctional potentials affected the pattern of myogenic electrical activity. Transmural stimulation could evoke premature slow waves in the myenteric portion of the circular layer but when excitatory inputs were blocked, IJPs greatly reduced the amplitude of slow waves. EJPs elicited action potentials in submucosal portion of circular muscles, and IJPs hyperpolarized these cells. The influence of intrinsic nerves on contractile patterns of pyloric muscles was also characterized. These data demonstrate that a neuromuscular apparatus exists within the gastroduodenal junction for 1) local regulation of slow waves and 2) independent control of the myenteric and submucosal regions of the circular layer.

Improved propagation in myometrium associated with gap junctions during parturition

1989 ◽  
Vol 256 (1) ◽  
pp. C130-C141 ◽  
Author(s):  
S. M. Miller ◽  
R. E. Garfield ◽  
E. E. Daniel
Keyword(s):  
Gap Junction ◽  
Electrical Coupling ◽  
Circular Muscle ◽  
Axial Direction ◽  
Muscle Layer ◽  
Circumferential Direction ◽  
Electrical Excitation ◽  
Myometrial Cells ◽  
Relaxation Oscillators ◽  
Junction Formation

The hypothesis that gap junction (GJ) formation between myometrial cells at term improves electrical coupling was tested. We measured the spread of electrical excitation from six extracellular electrodes aligned on uterine strips in either the longitudinal (axial) or transverse (circumferential) direction. Spontaneous bursts propagated over the entire 15-mm recording distance in the axial direction at both preterm and parturition and showed some characteristics of a system of coupled relaxation oscillators. However, individual spikes within the bursts propagated further and with higher velocity at parturition than at preterm. In the circumferential direction, both bursts and individual spikes propagated further at parturition than before. Propagation in this axis at parturition appeared to require an intact circular muscle layer. Spikes evoked by electrical stimulation also propagated further and with higher velocity in both axes at parturition. Electron microscopy showed many GJs between uterine smooth muscle cells during parturition, but few and sometimes no GJs at preterm. Thus improved propagation was associated with increased GJ contact between myometrial cells, consistent with the hypothesis that gap junction formation at term improves electrical coupling.

Electrical slow-wave activity from the circular layer of cat terminal antrum

1991 ◽  
Vol 261 (1) ◽  
pp. G78-G82
Author(s):  
L. M. Renzetti ◽  
M. B. Wang ◽  
J. P. Ryan
Keyword(s):  
Slow Wave ◽  
Circular Muscle ◽  
Muscle Cells ◽  
Muscle Layer ◽  
Wave Activity ◽  
Slow Waves ◽  
Slow Wave Activity ◽  
Plateau Phase ◽  
Circular Layer ◽  
Upstroke Velocity

Intracellular recording techniques were used to characterize the electrical slow-wave activity through the thickness of the circular muscle layer of the cat terminal antrum. Muscle strips were pinned out in cross section to the floor of a recording chamber perfused with Krebs buffer. Circular muscle cells from the myenteric to the submucosal border then were impaled with 20- to 40-M omega glass microelectrodes, and slow-wave activity was recorded. Slow waves from the myenteric side of the circular layer consisted of an upstroke depolarization, a prominent plateau phase, and a downstroke repolarization. Slow-wave characteristics for cells along the myenteric border were Em, -74.2 +/- 1.3 mV; duration, 5.3 +/- 0.5 s; upstroke amplitude, 29.4 +/- 3.4 mV; upstroke velocity, 0.20 +/- 0.03 V/s; and frequency, 5.8 +/- 0.5/min. Slow waves from muscle cells along the submucosal side of the preparation lacked a discernible plateau phase. Slow waves from submucosal border cells had the following characteristics: Em, -80.4 +/- 1.4 mV (P less than 0.01); duration, 3.5 +/- 0.4 s (P less than 0.01); upstroke amplitude, 44.0 +/- 2.4 mV (P less than 0.01); upstroke velocity, 0.56 +/- 0.06 V/s (P less than 0.01); and frequency, 4.2 +/- 0.4/min (P less than 0.05). Slow waves were not affected by 10(-7)M tetrodotoxin and 10(-6)M atropine or by removal of the longitudinal muscle layer. Slow-wave activity within each region was maintained after dissecting the circular layer into submucosal and myenteric segments. The results suggest that two distinct slow waves exist within the circular muscle layer of the cat terminal antrum.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in electrical and mechanical activity during ontogeny of the canine proximal colon

1996 ◽  
Vol 271 (1) ◽  
pp. G184-G191 ◽  
Author(s):  
S. M. Ward
Keyword(s):  
Membrane Potential ◽  
Circular Muscle ◽  
Electrical Field Stimulation ◽  
Muscle Layer ◽  
Proximal Colon ◽  
Mechanical Activity ◽  
Resting Membrane Potential ◽  
Circular Muscle Layer ◽  
Circular Layer ◽  
Spontaneous Contractions

The ontogenetic development of the circular muscle layer of the canine proximal colon was studied in animals from midway through gestation to 30 days old. With age, there was an increase in resting membrane potential along the submucosal surface and a decrease along the myenteric surface of the circular layer. Coinciding with the changes in membrane potential, slow waves increased in amplitude along the submucosal border and decreased in amplitude along the myenteric border. Muscle strips from animals midway through gestation were mechanically quiescent; however, 1 wk before birth spontaneous activity was observed. Electrical field stimulation of enteric nerves increased spontaneous contractions; this increase in activity was reversed to inhibition by atropine. In the presence of atropine and N omega-nitro-L-arginine or N omega-nitro-L-arginine methyl ester, a noncholinergic excitation was revealed at stimulation frequencies > 5 Hz. The results of these studies provide evidence that the canine proximal colon is spontaneously rhythmic and that a functional innervation to the circular muscle layer exists before birth. The gradient in resting membrane potential across the circular layer is absent at birth but develops within 2-3 wk after parturition.

Electrical coupling and pacemaker activity in colonic smooth muscle

1988 ◽  
Vol 255 (5) ◽  
pp. C653-C660 ◽  
Author(s):  
J. D. Huizinga ◽  
A. Shin ◽  
E. Chow
Keyword(s):  
Slow Wave ◽  
Electrical Coupling ◽  
Circular Muscle ◽  
Input Resistance ◽  
Wave Activity ◽  
Slow Wave Activity ◽  
Pacemaker Activity ◽  
Isolated Cells ◽  
Current Spread ◽  
Length Constant

The effect of heptanol on electrical coupling between submucosal circular muscle cells of the dog colon and consequences for slow-wave activity were investigated. Electrotonic potentials showed exponential decay giving a length constant of 2.6 +/- 0.5 mm and a time constant of 157 +/- 48 ms. Heptanol reversibly abolished electrotonic current spread, and subsequently no slow-wave activity was recorded. The length constant decreased to less than 0.2 mm. The input resistance increased from 3 to 36 M omega, suggesting a change from tissue syncytium to electrically isolated cells. D600 (5 X 10(-6) M) also abolished slow wave activity but had opposite effects on electrotonic current spread. The data are consistent with the hypothesis that heptanol reversibly inhibits intercellular coupling, resulting in loss of spread of extracellularly applied current, uncoupling of cells, and loss of pacemaker activity. Regulation of intercellular communication may be important in the control of intestinal motility.

Role of sodium pump in membrane potential gradient of canine proximal colon

1988 ◽  
Vol 254 (4) ◽  
pp. C475-C483 ◽  
Author(s):  
E. P. Burke ◽  
J. B. Reed ◽  
K. M. Sanders
Keyword(s):  
Membrane Potential ◽  
Potential Gradient ◽  
Circular Muscle ◽  
Bath Temperature ◽  
Muscle Layer ◽  
Membrane Potentials ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Circular Layer ◽  
External K

A large gradient in membrane potential exists through the thickness of the circular layer in canine colonic muscles. This study tested the effects of several experimental manipulations known to block electrogenic sodium pumping on the resting potentials of colonic muscles. Membrane potentials were recorded with microelectrodes from cells through the circular muscle layer. In cells adjacent to the submucosal surface of the circular layer, application of ouabain (10(-6) to 10(-5) M) caused an average membrane depolarization of 36 mV. Removal of the external K+ resulted in depolarizations similar to the effect of ouabain. Readmission of K+ (5.9 mM) produced repolarization and an additional hyperpolarization that averaged 13 mV beyond the resting potential. When exposed to 15 mM K+, cells hyperpolarized well beyond the estimated potassium equilibrium potential (EK). Ouabain blocked the repolarization in response to reintroduction of external K+. Lowering the bath temperature to 20 degrees C rapidly depolarized membrane potential; rewarming repolarized cells. Ouabain and K+-free solutions blocked the repolarization response to rewarming. Cells also depolarized when exposed to solutions in which the NaCl was replaced with LiCl. Membrane potentials of cells within the bulk of the circular layer decreased as a function of distance from the submucosal border. Cells at the myenteric border of the circular muscle were not significantly affected by ouabain and K+-free solution, but these treatments abolished the gradient in membrane potential across the circular layer.(ABSTRACT TRUNCATED AT 250 WORDS)

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