Date of Award
Doctor of Philosophy (PhD)
Dr. Jan D. Huizinga
The gastrointestinal (GI) tract is a hollow tubular organ that runs through the length of the central body. To move, mix, and compartmentalize ingesta through this tract, different patterns of motility are needed. This thesis is concerned with the myogenic control of motility through the pacemaker network of interstitial cells of Cajal (ICC) and the smooth muscle cells (SMC). Using patch clamp techniques, the electrophysiological properties of single ICC and SMC were examined. Previous research suggested the possibility of a specialized cell type generating the pacemaker slow wave potentials: the network of ICC that resides in the Auerbach's plexus region of the small intestine. An isolation procedure was developed and optimized to harvest single ICC that can survive short term culture and allow examination by patch clamp. Single cell patch clamp recordings demonstrated the presence of slow wave-like voltage oscillations driven by active current oscillations that match all properties seen in whole intestinal tissue slow waves. With different recording modes, whole cell currents, voltage and current oscillations were recorded from the same cell, showing that ICC are electrophysiologically unique and that the active inward current driving the slow wave-like oscillations are not voltage dependent. The isolated single ICC were demonstrated to have a specific tyrosine receptor marker protein for ICC, Kit , by selective RT-PCR amplification. The slow wave-like oscillations had a reversal potential consistent with a non-specific cation conductance. Although previous research had been done on single smooth muscle cells, there is currently no consensus on the cellular ionic currents present. In this thesis, analysis of different recordings demonstrated that there are at least four main groups of SMCs with different whole cell current profiles. Different cellular ionic currents were found specifically in different groups, and can be confirmed by reconstructing single channel recordings. One cellular outward current was chosen for further investigation-a fast activating and inactivating transient outward current. This current was characterized by common protocols and with a novel ramp analysis. Characterization revealed two distinct transient outward currents with different kinetic properties. Finally, spontaneous transient outward currents (STOCs) have been recorded in 25% of smooth muscle cells, reflecting quantal Ca2+ release from the intracellular stores to the plasmalemma calcium dependent potassium channels. Therefore, the study of STOCs gives direct information not only on the activities of intracellular Ca2+ stores, but also on the kinetics of Ca2+ release and reuptake in the microenvironment where STOCs originate. From these results, a simple model for GI motility was developed to account for the cellular interactions between nerve, ICC, and smooth muscle.
Fung Lee, Jonathan Cheuk, "Intrinsic electrophysiological properties of interstitial cells of Cajal and smooth muscle cells" (1999). Open Access Dissertations and Theses. Paper 1830.