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← Theoretical B

Q4 — Calcium Channel Signaling in Pancreatic Beta Cells

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Cell Signaling & Communication

A scientist in a lab is investigating two types of calcium channels in pancreatic beta cells. When Channel A opens, it allows an influx of calcium ions (Ca²⁺) into the cytosol. This rise in cytosolic Ca²⁺ triggers further calcium release from the endoplasmic reticulum (ER) via ryanodine and inositol trisphosphate receptors, and can activate Channel B to sustain the calcium signal. Mitochondria help modulate this calcium signaling by buffering excess Ca²⁺, which influences both energy production and cellular responses.

In mitochondria, calcium activates Krebs cycle enzymes (isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase), enhancing ATP production. Also, in these cells, calcium release triggers insulin release in response to high glucose levels.

Mitochondrial calcium in pancreatic beta cells was measured using a fluorescence microscope with a calcium sensor. Inhibitors used: Inhibitor X (Channel B blocker) and Inhibitor Y (Channel A blocker). Results are shown in the graph below:

A line graph of calcium concentration over time for four conditions (control, inhibitor X, inhibitor Y), all flat until a sharp spike after 30mM K+ is added, with the control and inhibitor X spiking higher than inhibitor Y. Figure 1. Calcium concentration under different conditions. A - control, B - inhibitor X, C - inhibitor Y, D - 30mM K+, E - calcium concentration (a.u.), F - time (mins). (cell media before D is applied: 2mM Ca2+, 5mM K+, low glucose)

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. In figure 1, cells depolarize after addition of 30mM K+.
B. From the experiment data provided we can conclude that the Channel A is ligand-gated.
C. If we performed a new experiment and replaced 30 mM K with high glucose in control conditions, the calcium concentration would not increase after high glucose stimulation.
D. If the same experiment as in Figure 1 was conducted in 0mM Ca2+ media, the response of the control cells would show a similar response to the inhibitor Y graph in Figure 1.
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Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF