Effect of 17beta-estradiol on insulin secretion and cytosolic calcium in Min6 mouse insulinoma cells and human islets of Langerhans.
OBJECTIVE
Female gonadal steroids can exert an insulinotropic effect in vivo. The objective of this study was to investigate the effects in vitro of 17-beta-estradiol (17beta-E2) on changes in cytosolic calcium ([Ca]i) and on insulin secretion from the MIN6 mouse insulinoma cell line and human primary islets of Langerhans.


METHODS
Stimulus-induced changes in [Ca]i were measured in Fura-2-loaded cells by single cell microfluorimetry. The effects of 17beta-E2 on insulin secretion were measured in static incubation experiments, and the rate and pattern of secretory responses were studied in multi-channel perifusion experiments.


RESULTS
17Beta-E2 (1-100 nmol/L) enhanced basal (2 mmol/L glucose) insulin secretion but had no effect on secretory responses to 20 mmol/L glucose or to depolarizing stimuli (100 micromol/L tolbutamide, 20 mmol/L KCl). Approximately 60% of MIN6 cells responded to 17beta-E2 (1-100 nmol/L) with a small but sustained increase in [Ca]i, whereas 98% of MIN6 cells responded to tolbutamide (100 micromol/L). Similar effects were observed in experiments using human primary beta cells. In contrast, 17beta-E2 had no detectable effect on the increases in [Ca]i evoked by tolbutamide (100 micromol/L) or glucose (20 mmol/L).


CONCLUSIONS
Our observations are consistent with a rapid effect of 17beta-E2 to depolarize beta cells leading to an influx of extracellular Ca and the initiation of insulin secretion by the consequent elevations in [Ca]i. We suggest that this may offer a mechanism through which circulating estradiol can influence beta-cell responsiveness to other signals.
Al-Majed
Hana T
HT
Division of Reproductive Health, Endocrinology and Development, King's College London, London, United Kingdom.
Squires
Paul E
PE
Persaud
Shanta J
SJ
Huang
Guo-Cai C
GC
Amiel
Stephanie
S
Whitehouse
Barbara J
BJ
Jones
Peter M
PM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D003600:Cytosol / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D007340:Insulinoma; D051379:Mice; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014044:Tolbutamide / Q000494:pharmacology
D007004:Hypoglycemic Agents; D007328:Insulin; D004958:Estradiol; D014044:Tolbutamide; D005947:Glucose; D002118:Calcium