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From depolarization-dependent contractions in gastrointestinal smooth muscle to aortic pulse-synchronized contractions.

Marion SB, Mangel AW - Clin Exp Gastroenterol (2014)

Bottom Line: On the basis of the frequency of these fast electrical events, we pursued, contrary to what has been established dogma for more than three centuries, the question of whether the smooth muscle wall of the aorta undergoes rhythmic activation during the cardiac cycle.As with depolarization-triggered contractile activity in gastrointestinal smooth muscle, it was "well known" that rhythmic activation of the aorta does not occur in synchrony with the heartbeat.The challenging of scientific dogma potentially leads to the expansion of our fundamental knowledge base.

View Article: PubMed Central - PubMed

Affiliation: RTI Health Solutions, Research Triangle Park, NC, USA.

ABSTRACT
For decades, it was believed that the diameter of gastrointestinal smooth muscle cells is sufficiently narrow, and that the diffusion of calcium across the plasma membrane is sufficient, to support contractile activity. Thus, depolarization-triggered release of intracellular calcium was not believed to be operative in gastrointestinal smooth muscle. However, after the incubation of muscle segments in solutions devoid of calcium and containing the calcium chelator ethylene glycol tetraacetic acid, an alternative electrical event occurred that was distinct from normal slow waves and spikes. Subsequently, it was demonstrated in gastrointestinal smooth muscle segments that membrane depolarization associated with this alternative electrical event triggered rhythmic contractions by release of intracellular calcium. Although this concept of depolarization-triggered calcium release was iconoclastic, it has now been demonstrated in multiple gastrointestinal smooth muscle preparations. On the basis of these observations, we investigated whether a rhythmic electrical and mechanical event would occur in aortic smooth muscle under the same calcium-free conditions. The incubation of aortic segments in a solution with no added calcium plus ethylene glycol tetraacetic acid induced a fast electrical event without corresponding tension changes. On the basis of the frequency of these fast electrical events, we pursued, contrary to what has been established dogma for more than three centuries, the question of whether the smooth muscle wall of the aorta undergoes rhythmic activation during the cardiac cycle. As with depolarization-triggered contractile activity in gastrointestinal smooth muscle, it was "well known" that rhythmic activation of the aorta does not occur in synchrony with the heartbeat. In a series of experiments, however, it was demonstrated that rhythmic contractions occur in the aortic wall in synchrony with the heartbeat and share a common pacemaker with the heart. We conclude that important observations in the vascular system became derivative from those in the gastrointestinal system. The challenging of scientific dogma potentially leads to the expansion of our fundamental knowledge base.

No MeSH data available.


Related in: MedlinePlus

Simultaneous recording of tension (upper) and blood pressure (lower) from the rabbit aorta in vivo.Notes: Vertical lines represent the onset of the pressure wave. Calibration bar: 0.6 g, 30 mmHg, 120 milliseconds. Basal blood pressure was 76 mmHg. The polarity of the upper trace was inverted from that originally recorded. Reproduced with permission from Mangel A, Fahim M, van Breemen C. Rhythmic contractile activity of the in vivo rabbit aorta. Nature. 1981;289(5799):692–694.20
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f4-ceg-7-061: Simultaneous recording of tension (upper) and blood pressure (lower) from the rabbit aorta in vivo.Notes: Vertical lines represent the onset of the pressure wave. Calibration bar: 0.6 g, 30 mmHg, 120 milliseconds. Basal blood pressure was 76 mmHg. The polarity of the upper trace was inverted from that originally recorded. Reproduced with permission from Mangel A, Fahim M, van Breemen C. Rhythmic contractile activity of the in vivo rabbit aorta. Nature. 1981;289(5799):692–694.20

Mentions: In contrast to the studies discussed earlier, on the basis of the fast rhythmic electrical activity observed in aortic muscle segments during incubation in calcium-free solution, Mangel et al19–21 directly measured tension changes in dog and rabbit aorta, femoral artery, and coronary artery in vivo. The initial experimental design involved bypassing the blood flow and recording tension changes in the bypassed segment. In the bypass tube, changes in arterial pressure were recorded. These experiments demonstrated a 1:1 coupling between pulse pressure changes and aortic, coronary, or femoral artery smooth muscle contractions. On the basis of the phasing of the pulse wave with the arterial contractions, these contractions were described as pulse-synchronized contractions (PSCs)21 (Figure 4).


From depolarization-dependent contractions in gastrointestinal smooth muscle to aortic pulse-synchronized contractions.

Marion SB, Mangel AW - Clin Exp Gastroenterol (2014)

Simultaneous recording of tension (upper) and blood pressure (lower) from the rabbit aorta in vivo.Notes: Vertical lines represent the onset of the pressure wave. Calibration bar: 0.6 g, 30 mmHg, 120 milliseconds. Basal blood pressure was 76 mmHg. The polarity of the upper trace was inverted from that originally recorded. Reproduced with permission from Mangel A, Fahim M, van Breemen C. Rhythmic contractile activity of the in vivo rabbit aorta. Nature. 1981;289(5799):692–694.20
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3974688&req=5

f4-ceg-7-061: Simultaneous recording of tension (upper) and blood pressure (lower) from the rabbit aorta in vivo.Notes: Vertical lines represent the onset of the pressure wave. Calibration bar: 0.6 g, 30 mmHg, 120 milliseconds. Basal blood pressure was 76 mmHg. The polarity of the upper trace was inverted from that originally recorded. Reproduced with permission from Mangel A, Fahim M, van Breemen C. Rhythmic contractile activity of the in vivo rabbit aorta. Nature. 1981;289(5799):692–694.20
Mentions: In contrast to the studies discussed earlier, on the basis of the fast rhythmic electrical activity observed in aortic muscle segments during incubation in calcium-free solution, Mangel et al19–21 directly measured tension changes in dog and rabbit aorta, femoral artery, and coronary artery in vivo. The initial experimental design involved bypassing the blood flow and recording tension changes in the bypassed segment. In the bypass tube, changes in arterial pressure were recorded. These experiments demonstrated a 1:1 coupling between pulse pressure changes and aortic, coronary, or femoral artery smooth muscle contractions. On the basis of the phasing of the pulse wave with the arterial contractions, these contractions were described as pulse-synchronized contractions (PSCs)21 (Figure 4).

Bottom Line: On the basis of the frequency of these fast electrical events, we pursued, contrary to what has been established dogma for more than three centuries, the question of whether the smooth muscle wall of the aorta undergoes rhythmic activation during the cardiac cycle.As with depolarization-triggered contractile activity in gastrointestinal smooth muscle, it was "well known" that rhythmic activation of the aorta does not occur in synchrony with the heartbeat.The challenging of scientific dogma potentially leads to the expansion of our fundamental knowledge base.

View Article: PubMed Central - PubMed

Affiliation: RTI Health Solutions, Research Triangle Park, NC, USA.

ABSTRACT
For decades, it was believed that the diameter of gastrointestinal smooth muscle cells is sufficiently narrow, and that the diffusion of calcium across the plasma membrane is sufficient, to support contractile activity. Thus, depolarization-triggered release of intracellular calcium was not believed to be operative in gastrointestinal smooth muscle. However, after the incubation of muscle segments in solutions devoid of calcium and containing the calcium chelator ethylene glycol tetraacetic acid, an alternative electrical event occurred that was distinct from normal slow waves and spikes. Subsequently, it was demonstrated in gastrointestinal smooth muscle segments that membrane depolarization associated with this alternative electrical event triggered rhythmic contractions by release of intracellular calcium. Although this concept of depolarization-triggered calcium release was iconoclastic, it has now been demonstrated in multiple gastrointestinal smooth muscle preparations. On the basis of these observations, we investigated whether a rhythmic electrical and mechanical event would occur in aortic smooth muscle under the same calcium-free conditions. The incubation of aortic segments in a solution with no added calcium plus ethylene glycol tetraacetic acid induced a fast electrical event without corresponding tension changes. On the basis of the frequency of these fast electrical events, we pursued, contrary to what has been established dogma for more than three centuries, the question of whether the smooth muscle wall of the aorta undergoes rhythmic activation during the cardiac cycle. As with depolarization-triggered contractile activity in gastrointestinal smooth muscle, it was "well known" that rhythmic activation of the aorta does not occur in synchrony with the heartbeat. In a series of experiments, however, it was demonstrated that rhythmic contractions occur in the aortic wall in synchrony with the heartbeat and share a common pacemaker with the heart. We conclude that important observations in the vascular system became derivative from those in the gastrointestinal system. The challenging of scientific dogma potentially leads to the expansion of our fundamental knowledge base.

No MeSH data available.


Related in: MedlinePlus