Abstract
In glucose-stimulated insulin secretion (GSIS) of pancreatic β-cells, the rise of free cytosolic Ca2+ concentration through voltage-gated calcium channels (VGCCs) triggers the exocytosis of insulin-containing granules. Recently, mechanically induced insulin secretion pathways were also reported, which utilize free cytosolic Ca2+ ions as a direct regulator of exocytosis. In this study, we aimed to investigate intracellular Ca2+ responses on the HIT-T15 pancreatic β-cell line upon low-intensity pulsed ultrasound (LIPUS) stimulation and found that ultrasound induces two distinct types of intracellular Ca2+ oscillation, fast-irregular and slow-periodic, from otherwise resting cells. Both Ca2+ patterns depend on the purinergic signaling activated by the rise of extracellular ATP or ADP concentration upon ultrasound stimulation, which facilitates the release through mechanosensitive hemichannels on the plasma membrane. Further study demonstrated that two subtypes of purinergic receptors, P2X and P2Y, are working in a competitive manner depending on the level of glucose in the cell media. The findings can serve as an essential groundwork providing an underlying mechanism for the development of a new therapeutic approach for diabetic conditions with further validation.
Highlights
Insulin, a peptide hormone secreted by the pancreas, plays a crucial role in maintaining the homeostasis of the blood glucose levels in the human body
The store-operated Ca2+ channels (SOCs) on the plasma membrane often serve as a Ca2+
When Ca2+ is released from intracellular storage, such as the endoplasmic reticulum (ER), SOCs are activated and allow Ca2+ entry into the cytoplasm and the storage
Summary
A peptide hormone secreted by the pancreas, plays a crucial role in maintaining the homeostasis of the blood glucose levels in the human body. It lowers the blood glucose levels by facilitating glucose uptakes in the liver, skeletal muscle, and adipose tissue. Failure to maintain blood glucose levels, known as hyperglycemia, can give rise to many different severe health conditions, including diabetes. Insulin secretion is stimulated by many different hormones and neurotransmitters such as glucagon-like peptide-1 [1] and carbon monoxide [2], but glucose is a major secretagogue.
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