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1 Department of Cell Biology and Physiology, Veterinary Faculty, Universitat Autónoma de Barcelona, 08193 Barcelona, Spain; and 2 Department of Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada L8N 3Z5
The structural and functional bases of
pacemaking (slow waves) in porcine ileal circular muscle were studied.
The myenteric plexus contained two, structurally distinct types of
interstitial cells of Cajal (ICC) interconnected by gap junctions and
connected by close contacts to muscle layers. At the deep muscular
plexus, ICC were present, not regularly close to nerve axons or in gap junction contact with one another or outer circular muscle, which had
many gap junctions. Slow waves (5.2 ± 2 mV amplitude and 4.6 ± 0.7 s duration) occurred at 9.9 ± 1.1 counts/min. Tissue length and
time constants were 2.00 ± 0.3 mm and 111 ± 37 ms,
respectively. Large electrical field-induced hyperpolarizations or
depolarizations reduced amplitudes but not frequencies or durations of
slow waves; hyperpolarizations progressively reduced inhibitory
junction potentials as if the K+
channel opening mediated them. In conclusion, the myenteric plexus ICC
of pig ileum, which appears to pace the muscle layers, appears insensitive to voltages applied to the syncytium of circular muscle cells. Limited coupling between ICC and circular muscle or
voltage-insensitive pacemaking activity may explain these findings.
interstitial cells of Cajal; pacemaking; electrical coupling; cable properties
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