Direct regulation of insulin secretion by angiotensin II in human islets of Langerhans.
OBJECTIVE
This study aimed to identify the expression of angiotensin II receptors in isolated human islets and beta cells and to examine the functional consequences of their activation.


METHODS
Single-cell RT-PCR was used to identify whether human islet cells express mRNA for type 1 angiotensin II receptors (AT(1)), and western blotting was used to determine AT(1) protein expression by human islets and MIN6 beta cells. We measured changes in intracellular calcium by microfluorimetry using Fura 2-loaded MIN6 cells and human islet cells. Dynamic insulin secretory responses were determined by RIA following perifusion of human islets and MIN6 cells.


RESULTS
Human islets expressed mRNAs for both the angiotensin precursor, angiotensinogen, and for angiotensin-converting enzyme. In addition, human and mouse beta cells expressed AT(1). These were functionally coupled to increases in intracellular calcium, which occurred at least in part through phospholipase-C-sensitive mechanisms and calcium influx through voltage-operated calcium channels. Short-term exposure of human islets and MIN6 cells to angiotensin II caused a rapid, short-lived initiation of insulin secretion at 2 mmol/l glucose and potentiation of insulin secretion induced by glucose (at 8 and 16.7 mmol/l).


CONCLUSIONS
These data demonstrate that the AT(1) is expressed by beta cells and that angiotensin II effects a short-lived and direct stimulation of human and mouse beta cells to promote insulin secretion, most probably through elevations in intracellular calcium. Locally produced angiotensin II may be important in regulating a coordinated insulin secretory response from beta cells.
Ramracheya
R D
RD
Beta Cell Development and Function Group, Division of Reproductive Health, Endocrinology and Development, King's College London, Room 2.9N Hodgkin Building Guy's Campus, London SE1 1UL, UK.
Muller
D S
DS
Wu
Y
Y
Whitehouse
B J
BJ
Huang
G C
GC
Amiel
S A
SA
Karalliedde
J
J
Viberti
G
G
Jones
P M
PM
Persaud
S J
SJ
D000802:Angiotensin Amide / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology* / Q000502:physiology; D000808:Angiotensinogen / Q000235:genetics / Q000502:physiology; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000032:analysis; D002460:Cell Line; D002478:Cells, Cultured; D005470:Fluorometry; D005786:Gene Expression Regulation; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D051379:Mice; D009543:Nifedipine / Q000494:pharmacology; D007703:Peptidyl-Dipeptidase A / Q000235:genetics / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D011945:Receptors, Angiotensin / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012504:Saralasin / Q000494:pharmacology
D007093:Imidazoles; D007328:Insulin; D011725:Pyridines; D012333:RNA, Messenger; D011945:Receptors, Angiotensin; D000808:Angiotensinogen; D000804:Angiotensin II; C073402:PD 123319; D000802:Angiotensin Amide; D007703:Peptidyl-Dipeptidase A; D012504:Saralasin; D009543:Nifedipine; D005947:Glucose; D002118:Calcium