Calcium-evoked insulin release from insulinoma cells is mediated via calcium-sensing receptor.
BACKGROUND
We have previously reported that high extracellular calcium ([Ca2+]o) levels elicited rapid increases in the cytosolic free calcium ([Ca2+]i) and insulin release from human insulinoma cells. In this study we further investigated the mechanism for stimulus-secretion coupling of insulinoma cells exposed to high levels of [Ca2+]o.


METHODS
Insulinoma tissues were surgically obtained for primary culture. The changes of [Ca2+]i level in response to various agents were monitored by fluorometry. Total RNA was extracted from tissues and subjected to reverse transcription-polymerase chain reaction (RT-PCR) with calcium-sensing receptor (CaR)-specific primers. PCR products were subcloned and sequenced.


RESULTS
When [Ca2+]o level was elevated, [Ca2+]i in insulinoma cells was immediately increased. Application of neomycin abolished the increase in [Ca2+]i level, although extracellular nifedipine and lanthanum chloride did not affect it. The depletion of intracellular calcium stores with thapsigargin or carbachol eliminated the increase in [Ca2+]i level. RT-PCR analysis identified the 682 bp product, of which the sequence was identical to the corresponding regions of human parathyroid CaR.


CONCLUSIONS
Intracellular Ca2+ release might be important in insulin release from insulinoma cells after exposing to high level of [Ca2+]o. CaR could be involved in this mechanism.
Kato
M
M
First Department of Surgery, Kyoto University, Japan.
Doi
R
R
Imamura
M
M
Furutani
M
M
Hosotani
R
R
Shimada
Y
Y
D000328:Adult; D015139:Blotting, Southern; D002118:Calcium / Q000502:physiology*; D005260:Female; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000378:metabolism*; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*
D007328:Insulin; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; D002118:Calcium