Ca super(2+) and electrolyte mobilization following agonist application to the pancreatic cell line HIT

• Published in: Pflügers Archiv Vol. 440; no. 6; pp. 828 - 834
• Main Authors: Nakagaki, Ikuko, Sasaki, Sadao, Hori, Seiki, Kondo, Hisao
• Format: Journal Article
• Language: English
• Published: 01.01.2000
• Subjects: glucagon-like peptide 1
• ISSN: 0031-6768
• DOI: 10.1007/s004240000372

We have investigated intracellular Ca super(2+) mobilization in oscillations of cytoplasmic Ca super(2+) in response to glucagon-like peptide 1 (GLP-1) and glucose in clonal HIT insulinoma cells with a confocal laser-scanning microscope (CLSM). We also used electron probe X-ray microanalysis to determine the GLP-1- and glucose-induced changes in electrolyte levels in the cytoplasm and insulin granules of the cells. GLP-1 produced 10- to 35-s duration oscillations in cytoplasmic Ca super(2+) concentration ([Ca super(2+)] sub(i)), both with and without Ca super(2+) in the extracellular solution, suggesting that Ca super(2+) is mobilized from intracellular Ca super(2+) stores, namely secretory granules. Glucose caused 1- to 3-min duration oscillatory increases in [Ca super(2+)] sub(i) when the extracellular solution contained Ca super(2+). When the cells were cultured without Ca super(2+) (no Ca super(2+) added, 1 mM EGTA), an oscillatory [Ca super(2+)] sub(i) increase of amplitude and short duration (12-35 s) was produced by 11 mM glucose, and the oscillation was inhibited by ruthenium red. X-ray microanalysis showed that stimulation with glucose increased the total Ca concentration in the cytoplasm and decreased it in the insulin granules with and without Ca super(2+) in the extracellular solution. The application of glucose significantly decreased K, and increased Na and Cl in the cytoplasm when the extracellular solution contained Ca super(2+). Our result also suggests that the [Ca super(2+)] sub(i) oscillation induced by glucose is involved in the release of Ca super(2+) from intracellular Ca super(2+) stores through the ryanodine receptor, which is blocked by ruthenium red, and/or through the inositol trisphosphate receptor that may be present in the membrane of insulin granules.