Calcium sensing by human medullary thyroid carcinoma cells

Area of Science:

• Endocrinology
• Cell Biology
• Oncology

Background:

• Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor originating from parafollicular C-cells.
• Understanding calcium homeostasis in MTC cells is crucial for elucidating tumor pathophysiology and potential therapeutic targets.

Purpose of the Study:

• To investigate the mechanisms regulating cytoplasmic calcium concentration ([Ca2+]i) in human MTC C-cells.
• To identify potential calcium-sensing mechanisms and ion channel activities involved in calcium regulation within MTC cells.

Main Methods:

• Fura-2 fluorescence imaging was used to measure [Ca2+]i in cultured C-cells from human MTC.
• Cells were subjected to various stimuli, including K+ depolarization, altered extracellular Ca2+ concentrations, and divalent cations (Sr2+, La3+, Ce3+).
• The effects of verapamil, a calcium channel blocker, were assessed.

Main Results:

• K+ depolarization induced a sustained increase in [Ca2+]i, which was reversible by verapamil.
• Elevating extracellular Ca2+ led to regular oscillations or steady-state increases in [Ca2+]i.
• Strontium (Sr2+) mimicked some Ca2+ actions, causing oscillations or steady-state increases in [Ca2+]i, partially reversible by verapamil.
• Lanthanum (La3+) and cerium (Ce3+) produced transient [Ca2+]i peaks independently of external Ca2+ but did not induce oscillations.

Conclusions:

• Human MTC cells possess a calcium-sensing mechanism analogous to that found in parathyroid cells.
• These cells exhibit both intracellular calcium mobilization and calcium influx pathways.
• Voltage-dependent calcium influx appears to play a significant role in the observed calcium oscillations in MTC cells.