Electrical coupling of circular muscle to longitudinal muscle and interstitial cells of Cajal in canine colon (original) (raw)
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Canadian Journal of Physiology and Pharmacology, 1992
of canine colon circu1ar muscle disconnected from the network of interstifa1 cells of Cajal. Can. J . Physiol. Pharmacol. 70: 289 -295. The 6 cpm omnipresent slow waves recorded in the circular muscle (CM) layer of canine colon are generated at the submucosal surhce of the CM layer. After removal of the submucosal network of interstitial cells of Cajal (ICC), 66% of the CM preparations (25 sf 38) were quiescent in Krebs solution. In the presence of cahachol, seven of nine sf these spntaneously quiescent CM preparations demonstrated slow wave-like activity with mean frequency, duration and amplitude of 5.9 + 0.4 cpm, 2.8 + 6.5 s, and 0.8 f 0.2 ~I V , 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 cprn, 2.7 + 0.5 s, and 1.0 + 0.2 mV, respectively, and by BaCB, (eight of eight quiescent CM preparations) with frequency, duration, and amplitude of 6.3 'r 0.3 cpm, I.$ f 0.2 s, and 0.5 + 0.1 mV, respectively. All the induced activities were abolished in the presence of H pM D6W. CM preparations with the submucosal ICC network intact (HCC -CM) showed slow wave activity in Krebs solution at a frequency of 6.2 t 0.2 cprn, a duration s f 3.6 f 0.2 s, and an amplitude of 1.0 + 0. I mV (n = 22). When ICC-CM preparations were stimulated by BaCl,, carbachol. or TEA, the slaw 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. The ability to generate slow wave-like activity after potassium conductance blockade in spontaneously quiescent CM disconnected from the ICC network suggested that circular muscle cells have ionic mechanisms for intrinsic oscillatory activity and are capable sf actively participating in the conduction and generation of slow waves. LILJ, L. W. C., DANIEL, E. E., et HL~IZINGA, 5. D. 1992. Excitability of canine colon circular nluscle disconnected from the network of interstital cells of Cajal. Can. J. Physiol. Pharmacol. 70 : 289-295. Les ondes Eentes ominipresentes de 6 cpm, enregistrtes dans la couche de muscle circulaire (MC) du colon du chien, sont produites i Ea surface sous-muqueuse de la couche de MC. Aprks l'extraction de cellules interstitielles de Cajal (CIC) du reseala sous-muqueux, 66% des preparations de MC (25 sur 38) ont Ct C inactives dans des solutions de Krebs. En presence de carbachol, sept SUH neuf de ces preparations de MC spontankment inactives ont dCmesntrC une activite de type onde lente, avec une frkquence, durte et amplitude moyennes de 5 ,0 f 0,4 cpm, 2,8 f 0,5 s et 0,8 i 0,2 mV, respectivernent. Des activitCs de type onde lente similaires ont tte iinduites par le TEA (sept sur huit des preparations inactives), avec une frtquence, durCe et amplitude de 6,1 f 0,2 cpm, 2,7 + 0,5 s et 1,0 f O,2 mV, respectivernent, et par le BaCl, (huit sur huit des pr6parations de MC inactives) avec une frequence, durte et amplitude de 6.3 + 0,3 cpm. 1,8 + 0,2 s et 0,5 f 0, I mV,
Intracellular electrical activity of canine and human gastric smooth muscle
The Journal of Physiology, 1978
Intracellular recordings were obtained from circular smooth muscle fibres of the canine fundus, corpus, antrum and pylorus as well as from the human corpus and antrum. 2. In the canine stomach, all regions of the stomach except the fundus exhibited spontaneous action potentials. 3. The spontaneous action potential consisted of an upstroke potential and a plateau potential. 4. There were regional differences in the configuration of the plateau potential. Corporal and antral smooth muscle did not normally spike during the plateau potential whereas terminal antral and pyloric muscle usually showed spikes on top of the plateau potential. Near the intermediate sphincter, there was a zone of transition in which oscillations in potential of variable amplitude were superimposed on the plateau potential. 5. The configuration of the action potential of the human stomach was similar to the configuration of the canine action potential when the same region of the stomach was compared. 6. The ionic dependence of the plateau potential was studied in canine stomach in an area where neither oscillations nor spikes occurred. 7. In calcium-free solution, all spontaneous activity stopped. D600 selectively suppressed the size of the plateau potential. 8. Sodium-deficient solution reduced the size of the plateau potential. 9. These results suggest that both calcium and sodium may be involved as current carriers in the generation of the plateau potential.
Electrical correlate of circumferential contractions in human colonic circular muscle
Gut, 1988
The role of myogenic electrical activity in the coordination of circumferential contraction of the human colon circular muscle was investigated. Five suction electrodes were placed (5-7 mm apart) on isolated rings of human colon and simultaneously electrical and motor activities were measured. In normal Krebs solution, the slow waves were not synchronised in most preparations studied. The electrical activities at the different recording sites were different with respect to slow wave frequency and amplitude, and amount of spiking activity. This resulted in irregular contractile activity. Cholinergic stimulation resulted in the development of a specific pattern of electrical activity: periodic slow wave activity with superimposed spiking activity which was synchronised over the length of the segment studied. This synchronised electrical activity resulted in regular phasic contractions at the frequency of the bursts of electrical activity (-1/min). The response to carbachol was mediated by muscarinic receptors since it was blocked by atropine. The periodic activity in the continuous presence of carbachol was not the result of periodic input of neural activity as it occurred in the presence of TTX. Intrinsic properties of the muscle cells were responsible for the carbachol induced pattern of activity. The present study presents evidence that the electrical correlate of circumferential contractions is different in man compared with the most commonly studied animal models. It is a specific, stimulus induced pattern of myogenic activity. Its characteristics closely resemble those of a particular pattern of in vivo recorded activity referred to as the 'long spike bursts'.
Dependence of electrical slow waves of canine colonic smooth muscle on calcium gradient
The Journal of physiology, 1992
1. The ionic dependence of the upstroke and plateau components of slow waves of canine colonic circular muscles was studied. 2. Reduced extracellular Ca2+ caused a decrease in the amplitude of the upstroke and plateau components, a decrease in the depolarization velocity, and a decrease in frequency. The reduction in the upstroke phase per 10-fold reduction in external Ca2+ was close to the value predicted by the Nernst relationship, suggesting that the membrane permeability to Ca2+ increases steeply during this phase. 3. Nifedipine (10(-9)-10(-6)) reduced the plateau component, but concentrations of 10(-6) M did not abolish the upstroke component. The data suggest that a nifedipine-resistant component of Ca2+ current may be involved in the upstroke. 4. Inorganic Ca2+ channel blockers (Mn2+ and Ni2+) blocked spontaneous slow waves at concentrations of 1.0 mM or less. 5. The upstroke component was more sensitive to Ni2+ than to Mn2+; a concentration of 0.040 mM-Ni2+ caused more than ...
Gradient in excitation-contraction coupling in canine gastric antral circular muscle
The Journal of Physiology, 1985
Slow waves decay in amplitude as they propagate through the thickness of circular muscle of the canine antrum. Slow waves are the excitable events that initiate contractions in the antrum. Excitation-contraction coupling occurs if slow wave depolarizations surpass a 'mechanical threshold'. 2. The amplitude of slow waves recorded from circular muscle cells near the submucosa was insufficient to reach the mechanical threshold previously determined for muscle near the myenteric plexus, suggesting that either submucosal cells are normally mechanically quiescent, or that contractions of submucosal cells are initiated at more polarized levels. 3. Experiments were performed to determine the voltage-tension relationships in adjacent 'myenteric' and 'submucosal' circular muscles. Membrane potentials of the muscles were depolarized by elevated concentrations of potassium. 4. Submucosal muscles were stimulated to contract at lower potassium concentrations than were myenteric muscles. Contractions of submucosal muscles at each potassium concentration studied were more forceful than contractions of myenteric muscles. 5. Plots of membrane potential vs. potassium concentration on a logarithmic scale showed that the membrane potential of myenteric cells was more dependent upon the potassium gradient than the membrane potential of submucosal cells. The potassium permeability of both groups of cells increased when depolarized, and the slopes of these plots approached Nernstian levels when depolarized below-55 mV. 6. Force developed in submucosal strips at more polarized levels than in myenteric muscles. The 'mechanical threshold' of submucosal muscles was 5-10 mV above resting potential, whereas myenteric muscles had to be depolarized by 25-30 mV before contraction was initiated. 7. The mechanisms responsible for the difference in mechanical thresholds are not known, but differences in the voltage dependence of calcium channels, in calcium release mechanisms, or in the sensitivity of the contractile proteins to calcium could be involved.
Spontaneous Electrical Activity of Interstitial Cells of Cajal Isolated from Canine Proximal Colon
Proceedings of The National Academy of Sciences, 1989
Interstitial cells of Cajal (ICC) have been suggested as pacemaker cells in the gastrointestinal tract. A method was developed to isolate ICC from the slow-wave pacemaker region of the canine proximal colon. These cells were identified under phase-contrast microscopy, and their identity was verified by comparing their ultrastructure with the morphology of ICC in situ. Patch-clamp experiments demonstrated that these cells are excitable; voltage-dependent inward and outward currents were elicited by depolarization. Inward current transients were identified as calcium currents. A portion of the outward current appears to be due to Ca21-
Neurogastroenterology and Motility, 2004
Considerable work has led many to conclude that interstitial cells of Cajal (ICC) are the pacemaker cells of the gastrointestinal (GI) tract. These cells form electrically coupled networks within the pacemaker regions of the GI tract, and ICC are electrically coupled to smooth muscle cells. ICC express unique ion channels that periodically produce inward (pacemaker) currents. Recent work has suggested that the inward current is produced by a calcium (Ca 2+ )-regulated, nonselective cation conductance. Channels responsible for this conductance oscillate in open probability in response to the periodic drop in intracellular Ca 2+ concentration during the slow wave cycle. Pacemaker activity generates slow waves that are propagated actively through ICC networks. Depolarization coordinates the pacemaker activity through the ICC network by activating a dihydropyridine-resistant Ca 2+ conductance. Entry of small amounts of Ca 2+ into ICC entrains spontaneous pacemaker activity and produces cell-to-cell propagation of slow waves. This review discusses the mechanisms and conductances involved in generation and propagation of electrical slow waves in ICC.