Recent reports using immunohistochemistry have shown that
Galphaolf which shares 88% homology with Galphas was expressed in pancreatic islets. To test the specificity of the expression of this
G protein isotype in rat islet cells, B and non-B cells were separated by flow cytometry. The expression of
Galphaolf and
adenylyl cyclases (AC) of types II, III, V, and VI was evaluated by
reverse-transcriptase polymerase chain reaction (RT-PCR). Since alterations in the expression of AC III were recently reported in the GK rat (a model of
non-insulin-dependent diabetes mellitus,
NIDDM), we also have analyzed the
mRNA expression of
Galphaolf and AC
isoforms in pancreatic islets from GK rats and from adult rats neonatally treated by
streptozotocin (nSTZ rats), another model of
NIDDM. Southern blots of amplicons generated with specific primers of
Galphaolf revealed the presence of a 540-bp band only in B cells. AC of types II, III, V, and VI were expressed both in B and non-B cells. However, AC III
mRNA was clearly more abundant in non-B than in B cells. Moreover, in B cells the expression of AC VI was higher than that of AC V, whereas equal expressions of AC V and AC VI were found in non-B cells. In GK rat islets, the
mRNA expressions of
Galphaolf, AC II, and AC III were clearly increased and no change in AC V and AC VI was found. In nSTZ rat islets,
Galphaolf expression was barely detectable, but AC II and AC III
mRNA levels were higher than those observed in controls. In conclusion,
Galphaolf mRNA appeared specifically expressed in islet B cells and was increased in GK islets. The steady-state
mRNA levels of AC II and AC III were clearly increased in the islets of the two rat models of
NIDDM. Thus, alterations in the expression of
G protein isotypes and AC
isoforms could contribute to the diabetic phenotype.