GI system: Pancreatitis studies

Pancreatitis is a disease in which the pancreas self-digests. Typically, digestive enzymes inside the pancreas are in an inactive form – the so-called zymogen form. The pancreas secretes these zymogens into the small intestine, where they are activated to become fully functional enzymes. Inside the pancreas, zymogens and other digestive enzymes, such as pancreatic amylase, are packaged together inside secretory organelles called zymogen granules. Failure to secrete zymogen granules may eventually result in activated digestive enzymes inside the pancreas, which can cause pancreatitis.

It is thought that the inositol trisphosphate (IP3) pathway regulates the release of zymogen granules. In the IP3 pathway, the activation of a G-protein via a muscarinic M3 receptor releases inositol trisphosphate (IP3) into the cytosol. The IP3 molecule then binds to an IP3 receptor, opening calcium channels. As a result of these events, zymogen granules are released.

Researchers have identified two IP3 receptors that are prevalent in pancreatic cells: IP3R-2 and IP3R-3. To explore the role of these two receptors, researchers created genetically engineered mice with knockouts (KOs) in the IP3R-2 and IP3R-3 genes. Next, they performed the following experiments, comparing wild-type mice to mice with IP3R-2 and/or IP3R-3 knockouts.

Researchers extracted pancreatic cells from mice in each of the four groups (wild type, IP3R-2 KO, IP3R-3 KO and IP3R-2/IP3R-3 double KO). The cells were simulated with carbachol (CCh), a cholinergic stimulant. Figure 1 shows the percent increase in amylase over baseline, after 30 minutes of exposure to carbachol.

Figure 1 Percent increase in amylase release after 30 minutes of exposure to carbachol

Researchers exposed pancreatic cells to increasing levels of acetylcholine (ranging from 0.1 μM to 3 μM). Changes in cytosolic $C{a}^{2+}$‍ levels were monitored and recorded. The results are shown in Figure 2.

Figure 2 Cytosolic $C{a}^{2+}$‍ concentrations over time; arrows indicate the addition of acetylcholine