Abstract
Glucagon, secreted by the pancreatic α-cells, stimulates insulin secretion from neighboring β-cells by CAMP- and protein kinase A (PKA)-dependent mechanisms, but it is not known whether glucagon also modulates its own secretion. We have addressed this issue by combining recordings of membrane capacitance (to monitor exocytosis) in individual α-cells with biochemical assays of glucagon secretion and cAMP content in intact pancreatic islets, as well as analyses of glucagon receptor expression in pure α-cell fractions by RT-PCR. Glucagon stimulated cAMP generation and exocytosis dose dependently with an EC50 of 1.6-1.7 nM. The stimulation of both parameters plateaued at concentrations beyond 10 nM of glucagon where a more than 3-fold enhancement was observed. The actions of glucagon were unaffected by the GLP-1 receptor antagonist exendin-(9-39) but abolished by des-His 1-[Glu9]-glucagonamide, a specific blocker of the glucagon receptor. The effects of glucagon on α-cell exocytosis were mimicked by forskolin and the stimulatory actions of glucagon and forskolin on exocytosis were both reproduced by intracellular application of 0.1 mM cAMP. cAMP-potentiated exocytosis involved both PKA-dependent and -independent (resistant to Rp-cAMPS, an Rp-isomer of cAMP) mechanisms. The presence of the cAMP-binding protein cAMP-guanidine nucleotide exchange factor II in α-cells was documented by a combination of immunocytochemistry and RT-PCR and 8-(4-chloro-phenylthio)-2′-O-methyl-cAMP, a cAMP-guanidine nucleotide exchange factor II-selective agonist, mimicked the effect of cAMP and augmented rapid exocytosis in a PKA-independent manner. We conclude that glucagon released from the α-cells, in addition to its well-documented systemic effects and paracrine actions within the islet, also represents an autocrine regulator of α-cell function.
| Original language | English |
|---|---|
| Pages (from-to) | 198-212 |
| Number of pages | 15 |
| Journal | Molecular Endocrinology |
| Volume | 19 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 1 2005 |
| Externally published | Yes |
Fingerprint
ASJC Scopus subject areas
- Molecular Biology
- Endocrinology, Diabetes and Metabolism
Cite this
Glucagon stimulates exocytosis in mouse and rat pancreatic α-cells by binding to glucagon receptors. / Ma, Xiaosong; Zhang, Yang; Gromada, Jesper; Sewing, Sabine; Berggren, Per Olof; Buschard, Karsten; Salehi, Albert; Vikman, Jenny; Rorsman, Patrik; Eliasson, Lena.
In: Molecular Endocrinology, Vol. 19, No. 1, 01.01.2005, p. 198-212.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Glucagon stimulates exocytosis in mouse and rat pancreatic α-cells by binding to glucagon receptors
AU - Ma, Xiaosong
AU - Zhang, Yang
AU - Gromada, Jesper
AU - Sewing, Sabine
AU - Berggren, Per Olof
AU - Buschard, Karsten
AU - Salehi, Albert
AU - Vikman, Jenny
AU - Rorsman, Patrik
AU - Eliasson, Lena
PY - 2005/1/1
Y1 - 2005/1/1
N2 - Glucagon, secreted by the pancreatic α-cells, stimulates insulin secretion from neighboring β-cells by CAMP- and protein kinase A (PKA)-dependent mechanisms, but it is not known whether glucagon also modulates its own secretion. We have addressed this issue by combining recordings of membrane capacitance (to monitor exocytosis) in individual α-cells with biochemical assays of glucagon secretion and cAMP content in intact pancreatic islets, as well as analyses of glucagon receptor expression in pure α-cell fractions by RT-PCR. Glucagon stimulated cAMP generation and exocytosis dose dependently with an EC50 of 1.6-1.7 nM. The stimulation of both parameters plateaued at concentrations beyond 10 nM of glucagon where a more than 3-fold enhancement was observed. The actions of glucagon were unaffected by the GLP-1 receptor antagonist exendin-(9-39) but abolished by des-His 1-[Glu9]-glucagonamide, a specific blocker of the glucagon receptor. The effects of glucagon on α-cell exocytosis were mimicked by forskolin and the stimulatory actions of glucagon and forskolin on exocytosis were both reproduced by intracellular application of 0.1 mM cAMP. cAMP-potentiated exocytosis involved both PKA-dependent and -independent (resistant to Rp-cAMPS, an Rp-isomer of cAMP) mechanisms. The presence of the cAMP-binding protein cAMP-guanidine nucleotide exchange factor II in α-cells was documented by a combination of immunocytochemistry and RT-PCR and 8-(4-chloro-phenylthio)-2′-O-methyl-cAMP, a cAMP-guanidine nucleotide exchange factor II-selective agonist, mimicked the effect of cAMP and augmented rapid exocytosis in a PKA-independent manner. We conclude that glucagon released from the α-cells, in addition to its well-documented systemic effects and paracrine actions within the islet, also represents an autocrine regulator of α-cell function.
AB - Glucagon, secreted by the pancreatic α-cells, stimulates insulin secretion from neighboring β-cells by CAMP- and protein kinase A (PKA)-dependent mechanisms, but it is not known whether glucagon also modulates its own secretion. We have addressed this issue by combining recordings of membrane capacitance (to monitor exocytosis) in individual α-cells with biochemical assays of glucagon secretion and cAMP content in intact pancreatic islets, as well as analyses of glucagon receptor expression in pure α-cell fractions by RT-PCR. Glucagon stimulated cAMP generation and exocytosis dose dependently with an EC50 of 1.6-1.7 nM. The stimulation of both parameters plateaued at concentrations beyond 10 nM of glucagon where a more than 3-fold enhancement was observed. The actions of glucagon were unaffected by the GLP-1 receptor antagonist exendin-(9-39) but abolished by des-His 1-[Glu9]-glucagonamide, a specific blocker of the glucagon receptor. The effects of glucagon on α-cell exocytosis were mimicked by forskolin and the stimulatory actions of glucagon and forskolin on exocytosis were both reproduced by intracellular application of 0.1 mM cAMP. cAMP-potentiated exocytosis involved both PKA-dependent and -independent (resistant to Rp-cAMPS, an Rp-isomer of cAMP) mechanisms. The presence of the cAMP-binding protein cAMP-guanidine nucleotide exchange factor II in α-cells was documented by a combination of immunocytochemistry and RT-PCR and 8-(4-chloro-phenylthio)-2′-O-methyl-cAMP, a cAMP-guanidine nucleotide exchange factor II-selective agonist, mimicked the effect of cAMP and augmented rapid exocytosis in a PKA-independent manner. We conclude that glucagon released from the α-cells, in addition to its well-documented systemic effects and paracrine actions within the islet, also represents an autocrine regulator of α-cell function.
UR - http://www.scopus.com/inward/record.url?scp=19944427738&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=19944427738&partnerID=8YFLogxK
U2 - 10.1210/me.2004-0059
DO - 10.1210/me.2004-0059
M3 - Article
C2 - 15459251
AN - SCOPUS:19944427738
VL - 19
SP - 198
EP - 212
JO - Molecular Endocrinology
JF - Molecular Endocrinology
SN - 0888-8809
IS - 1
ER -