Direct regulation of insulin secretion by angiotensin II in human islets of Langerhans

Abstract

Aims/hypothesis: 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. Materials and methods: Singlecell 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/interpretation: 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.

The Role of Arachidonic Acid and Its Metabolites in Insulin Secretion From Human Islets of Langerhans

“…However, the expression by human islets of other PGE 2 receptor family members that are associated with stimulation of second messenger generation may explain why PGE 2 did not inhibit glucose-induced insulin secretion and stimulated basal insulin secretion from human ␤-cells. With regard to this, PGE 2 may be operating through EP1 receptors to elevate intracellular Ca 2ϩ , as has been observed in other cell types (38), and agonists that increase Ca 2ϩ in human islets can initiate insulin secretion at substimulatory glucose concentrations (26,39,40).…”

“…All products were cut from the gels and spin column purified using a QIAquick gel extraction kit, and identities were confirmed by sequencing on an ABI 377 using fluorescent chain-terminator methods. In some PCRs, template cDNA obtained from single human islet cells (26) was amplified using the COX-2 primer sets listed in Table 1. Insulin secretion.…”

Effect of acute hyperinsulinaemia with and without angiotensin II type 1 receptor blockade on resistin and adiponectin concentrations and expressions in healthy subjects

“…There were no changes in body weight between the clamps, and therefore, the insulin infusion rates were comparable for both clamps. Higher insulin levels after losartan administration cannot be explained by involvement of insulin secretion, because angiotensin II receptor activation, not inhibition, was shown to stimulate insulin secretion (46). Impairment of insulin clearance in liver by ARB cannot be excluded, but there is no corresponding data available.…”

Identification of Insulin Signaling Elements in Human β-Cells

“…Single-cell RT-PCR. Between 48 and 72 h after islet isolation, 10 -20 handpicked islet equivalents were dispersed into cell suspensions by trypsinization and RT-PCR amplification of mRNAs isolated from single human islet cells was performed essentially as previously described (14). The first round of PCR amplification was performed for 45 cycles using 3-5 l of the RT reaction by the addition of 40 l of PCR mixture containing a final concentration of 0.5 mol/l of the specific outer primers, 0.15 mol/l of each dNTP, and 2.5 units of TaqDNA polymerase.…”