Expression of transient receptor potential ankyrin 1 (TRPA1) and its role in insulin release from rat pancreatic beta cells.
OBJECTIVE
Several transient receptor potential (TRP) channels are expressed in pancreatic beta cells and have been proposed to be involved in insulin secretion. However, the endogenous ligands for these channels are far from clear. Here, we demonstrate the expression of the transient receptor potential ankyrin 1 (TRPA1) ion channel in the pancreatic beta cells and its role in insulin release. TRPA1 is an attractive candidate for inducing insulin release because it is calcium permeable and is activated by molecules that are produced during oxidative glycolysis.


METHODS
Immunohistochemistry, RT-PCR, and Western blot techniques were used to determine the expression of TRPA1 channel. Ca²⁺ fluorescence imaging and electrophysiology (voltage- and current-clamp) techniques were used to study the channel properties. TRPA1-mediated insulin release was determined using ELISA.


RESULTS
TRPA1 is abundantly expressed in a rat pancreatic beta cell line and freshly isolated rat pancreatic beta cells, but not in pancreatic alpha cells. Activation of TRPA1 by allyl isothiocyanate (AITC), hydrogen peroxide (H₂O₂), 4-hydroxynonenal (4-HNE), and cyclopentenone prostaglandins (PGJ₂) and a novel agonist methylglyoxal (MG) induces membrane current, depolarization, and Ca²⁺ influx leading to generation of action potentials in a pancreatic beta cell line and primary cultured pancreatic beta cells. Activation of TRPA1 by agonists stimulates insulin release in pancreatic beta cells that can be inhibited by TRPA1 antagonists such as HC030031 or AP-18 and by RNA interference. TRPA1-mediated insulin release is also observed in conditions of voltage-gated Na⁺ and Ca²⁺ channel blockade as well as ATP sensitive potassium (K(ATP)) channel activation.


CONCLUSIONS
We propose that endogenous and exogenous ligands of TRPA1 cause Ca²⁺ influx and induce basal insulin release and that TRPA1-mediated depolarization acts synergistically with K(ATP) channel blockade to facilitate insulin release.
Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, United States of America. dcao@ucsd.edu
De-Shou
DS
Cao
Linlin
L
Zhong
Tsung-Han
TH
Hsieh
Mruvil
M
Abooj
Mahendra
M
Bishnoi
Lauren
L
Hughes
Louis S
LS
Premkumar
D000447:Aldehydes / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism*; D017879:Isothiocyanates / Q000494:pharmacology; D015230:Prostaglandin D2 / Q000031:analogs & derivatives / Q000494:pharmacology; D011765:Pyruvaldehyde / Q000494:pharmacology; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels / Q000235:genetics / Q000378:metabolism*
D000447:Aldehydes; D007328:Insulin; D017879:Isothiocyanates; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; C480976:Trpa1 protein, rat; C037112:9-deoxy-delta-9-prostaglandin D2; D011765:Pyruvaldehyde; D006861:Hydrogen Peroxide; C004471:allyl isothiocyanate; C027576:4-hydroxy-2-nonenal; D015230:Prostaglandin D2; D002118:Calcium