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Propagation of pacemaker activity in the guinea‐pig antrum
Author(s) -
Hennig G. W.,
Hirst G. D. S.,
Park K. J.,
Smith C. B.,
Sanders K. M.,
Ward S. M.,
Smith T. K.
Publication year - 2004
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.059055
Subject(s) - interstitial cell of cajal , antrum , peristalsis , depolarization , pacemaker potential , myenteric plexus , anatomy , chemistry , guinea pig , electrophysiology , medicine , biophysics , physics , smooth muscle , biology , stomach , immunohistochemistry
Cyclical periods of depolarization (slow waves) underlie peristaltic contractions involved in mixing and emptying of contents in the gastric antrum. Slow waves originate from a myenteric network of interstitial cells of Cajal (ICC‐MY). In this study we have visualized the sequence and propagation of Ca 2+ transients associated with pacemaker potentials in the ICC network and longitudinal (LM) and circular muscle (CM) layers of the isolated guinea‐pig gastric antrum. Gastric antrum was dissected to reveal the ICC‐MY network, loaded with Fluo‐4 AM and activity was monitored at 37°C. Ca 2+ waves propagated throughout the ICC‐MY network at an average velocity of 3.24 ± 0.12 mm s −1 at a frequency of 4.87 ± 0.16 cycles min −1 ( n = 4). The propagation of the Ca 2+ wave often appeared ‘step‐like’, with separate regions of the network being activated after variable delays. The direction of propagation was highly variable (Δ angle of propagation 44.3 ± 10.9 deg per cycle) and was not confined to the axes of the longitudinal or circular muscle. Ca 2+ waves appeared to spread out radially from the site of initiation. The initiating Ca 2+ wave in ICC‐MY was correlated to secondary Ca 2+ waves in intramuscular interstial cells of Cajal, ICC‐IM, and smooth muscle cells, and the local distortion (contraction) in a field of view. TTX (1 μ m ) had little effect on slow wave or pacemaker potential activity, but 2‐APB (50 μ m ) blocked all Ca 2+ waves, indicating a pivotal role for intracellular Ca 2+ stores. Nicardipine (2 μ m ) eliminated the Ca 2+ transient generated by smooth muscle, but did not affect the fast upstroke associated with ICC‐MY. These results indicate that slow waves follow a sequence of activation, beginning with the ICC‐MY and ICC‐IM network, followed later by a sustained Ca 2+ transient in the muscle layers that is responsible for contraction.