FIGURE 12. Slow wave and smooth muscle contraction.


Slow wave and smooth muscle contraction. (A) The slow wave depolarizes the smooth muscle membrane in the range of about –40mV to –50 mV from a resting membrane potential in the range of –60 mV to –80 mV. However, as shown in (B), this depolarization induces very small inward calcium current (electromechanical coupling). Therefore, slow-wave depolarization by itself generates a very tiny contraction. Any ACh released during the slow-wave depolarization induces additional calcium influx through calcium channels as well as calcium release from the endoplasmic stores. In addition, the cell-signaling pathways initiated by the binding of ACh to muscarinic M3 receptors increases calcium sensitivity to further enhance contraction amplitude (pharmacomechanical coupling). The electromechanical and pharmacomechanical couplings together (see Figure 11) generate the postprandial contractions, which are of sufficient amplitude and duration to cause mixing/turning over and propulsion of the digesta. (Reproduced with permission from Sarna, SK, Am J Physiol Gastrointest Liver Physiol, 294: 372–390, 2008 [79].)

From: Regulatory Mechanisms

Cover of Colonic Motility
Colonic Motility: From Bench Side to Bedside.
Sarna SK.
San Rafael (CA): Morgan & Claypool Life Sciences; 2010.
Copyright © 2010 by Morgan & Claypool Life Sciences.

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