Pancreatic alpha- and beta-cells play vital roles in maintaining glucose homeostasis. While much work has investigated beta-cell biology, alpha-cell research has been scarce. This is due to limitations in conventional methods of alpha-cell preparation, which expose alpha-cells on the islet mantle to enzymatic and mechanical injury inherent in the preparation. I have employed the pancreas tissue slice preparation, which surmounts these limitations. Pancreas slices can be prepared efficiently, and islet cells examined in situ without requiring culture conditions. Alpha-cells are preserved in their native cellular environment not only in health, but more remarkably, also in disease (type 1 diabetes; T1D) states, which was not previously feasible.
In the first part of my study, I deployed this preparation to assess normal mouse alpha-cell physiology. Alpha-cells exhibited well-described features of INa, IKATP, small cell size, low resting membrane conductance, and inducible low and high voltage-activated ICa, the latter correlating with exocytosis determined by capacitance measurements. In contrast to previous reports, our large sampling of alpha-cells revealed a wide-range data distribution of several ion channel parameters. My findings explain the apparent inconsistency of previous reports wherein alpha-cell ion channel properties appeared skewed within narrow portions of this wide distribution, likely caused by different preparations.
In the second part of my thesis, I assessed alpha-cell perturbation in streptozotocin-induced T1D in the GluCre-ROSA26EYFP (GYY) mouse. In this T1D model, alpha-cells exhibited more glucagon content per cell, which can be exocytosed in greater quantity upon serial depolarization. Membrane electrical properties revealed larger Na+ current and reduced KV-transient current, which contributed to the apparent increased amplitude and firing frequency of action potentials in membrane electrical recording. These electrical events likely prime alpha-cells to release more glucagon, culminating in larger in vivo glucagon secretory responses to low glucose stimulation in this T1D model.
We are now well-positioned to employ this in situ model of pancreas slice preparation to address many other apparently unanswerable questions in alpha-cells in normal and pathophysiologic states, such as diabetes.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/32741 |
| Date | 22 August 2012 |
| Creators | Ya-Chi, Huang |
| Contributors | Herbert, Gaisano |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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