Expression of carbonic anhydrase V in pancreatic beta cells suggests role for mitochondrial carbonic anhydrase in insulin secretion.
Carbonic anhydrase V (CA-V) is a mitochondrial enzyme that provides bicarbonate for pyruvate carboxylase in liver and kidney. In the course of a survey of the tissue distribution of CA-V, we detected intense immunostaining in pancreatic islets when sections from rat and mouse pancreases were reacted with a polyclonal antibody to recombinant mouse CA-V. The distribution and large number of CA-V-positive cells in each islet suggested that they represented beta cells. Double immunofluorescence staining of tissue sections and isolated islet cells showed cellular colocalization of CA-V and insulin, confirming that beta cells contain CA-V. Western blotting of rat islets of Langerhans and primary beta cells showed 33- and 30-kDa polypeptides of precursor and mature CA-V, respectively. The CA-V expression was beta cell-specific since no CA-V immunoreaction was detected in the primary alpha cells. Immunohistochemical staining for CA-I, CA-II, CA-IV, CA-VI, and CA-IX was negative in beta cells, and Western blotting of beta cells also failed to identify any CA in beta cells except CA-V. The specific localization of CA-V in beta cells led us to hypothesize that CA-V may be functionally linked to the regulation of insulin secretion. Consistent with this hypothesis, the CA inhibitor acetazolamide was found to be a strong inhibitor of glucose-stimulated insulin secretion by isolated rat pancreatic islets.
Parkkila
A K
AK
Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104, USA.
Scarim
A L
AL
Parkkila
S
S
Waheed
A
A
Corbett
J A
JA
Sly
W S
WS
D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D002256:Carbonic Anhydrases / Q000032:analysis / Q000378:metabolism*; D004792:Enzyme Precursors / Q000032:analysis; D005947:Glucose / Q000494:pharmacology / Q000502:physiology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D007527:Isoenzymes / Q000032:analysis / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D004792:Enzyme Precursors; D007328:Insulin; D007527:Isoenzymes; D002256:Carbonic Anhydrases; D005947:Glucose; D000086:Acetazolamide