Ab. Ropero et al., Non-genomic actions of 17 beta-oestradiol in mouse pancreatic beta-cells are mediated by a cGMP-dependent protein kinase, J PHYSL LON, 521(2), 1999, pp. 397-407
1. Intracellular calcium concentration ([Ca2+](i)) was measured in mouse wh
ole islets of Langerhans using the calcium-sensitive fluorescent dye Indo-1
.
2. Application of physiological concentrations of 17 beta-oestradiol in the
presence of a stimulatory glucose concentration (8 mM) potentiated the [Ca
2+](i) signal in 83% of islets tested. Potentiation was manifested as eithe
r an increase in the frequency or duration of [Ca2+](i) oscillations.
3. The effects caused by 17 beta-oestradiol were mimicked by the cyclic nuc
leotide analogues 8-bromoguanosine-3',5'-cyclic monophosphate (8-Br-cGMP) a
nd 8-bromoadenosine-3',5'-cyclic monophosphate (8-Br-cAMP).
4. Direct measurements of both cyclic nucleotides demonstrated that nanomol
ar concentrations of 17 beta-oestradiol in the presence of 8 mM glucose inc
reased cGMP levels, yet cAMP levels were unchanged. The increment in cGMP w
as similar to that induced by 11 mM glucose.
5. Patch-clamp recording in intact cells showed that 8-Br-cGMP reproduced t
he inhibitory action of 17 beta-oestradiol on ATP-sensitive K+ (K-ATP) chan
nel activity This was not a membrane-bound effect since it could not be obs
erved in excised patches.
6. The action of 17 beta-oestradiol on K-ATP channel activity was not modif
ied by the specific inhibitor of soluble guanylate cyclase (sGC) LY 83583.
This result indicates a likely involvement of a membrane guanylate cyclase
(mGC).
7. The rapid decrease in K-ATP channel activity elicited by 17 beta-oestrad
iol was greatly reduced using Rp-8-pCPT-cGMPS, a specific blocker of cGMP-d
ependent protein kinase (PKG). Conversely, Rp-cAMPS, which inhibits cAMP-de
pendent protein kinase (PKA), had little effect,
8. The results presented here indicate that rapid, non-genomic effects of 1
7 beta-oestradiol after interaction with its binding site at the plasma mem
brane of pancreatic beta-cells is a cGMP-dependent phosphorylation process.