17 beta-oestradiol increases intracellular Ca2+ concentration in rat enterocytes - Potential role of phospholipase C-dependent store-operated Ca2+ influx

The involvement of the phospholipase C (PLC) pathway in the non-genomic reg ulation of duodenal cell Ca2+ concentration by 17 beta-oestradiol was inves tigated. The PLC inhibitors neomycin (0.5 mM) and U-73122 (2 mu M) suppress ed the stimulatory effect of 0.1 nM 17 beta-oestradiol on the Ca-45(2+) inf lux into enterocytes isolated from rat duodenum. The hormone (1 pM to 10 nM ) increased the formation of 1,2-diacylglycerol in a biphasic pattern, char acterized by an early peak at 45 s (+82%,) and a later peak at 5 min (+46%, ). Both PLC inhibitors suppressed the first peak but were unable to block t he 17 beta-oestradiol effect at 5 min. 17 beta-Oestradiol also increased th e generation of inositol 1,4,5-trisphosphate within 15 s, with maximal stim ulation at 30 s. 17 beta-Oestradiol induced a rapid (30 s) and sustained (u p to 5 min) increase in the intracellular Ca2+ concentration ([Ca2+](i)) of fura 2-loaded enterocytes. The fast rise in [Ca2+](i) was specific because other sex steroid hormones were without effect and could be blocked to a g reat extent by U-73122 (by 86%, at 1 min). The effects of 17 beta-oestradio l on enterocyte [Ca2+](i) were decreased significantly (by 75%) in a Ca2+-f ree extracellular medium but a pronounced increase in [Ca2+](i) was obtaine d after readmission of Ca2+ to the medium. The latter change was suppressed by 10 mu M La3+, whereas nitrendipine (1 mu M) and verapamil (10 mu M) sep arately were without effect. The permeability of the 17 beta-oestradiol-ind uced Ca2+ influx pathway to Mn2+ was increased 2.8-fold by treatment with o estrogen. These results suggest the operation of a PLC-dependent store-oper ated Ca2+ channel mechanism in 17 beta-oestradiol regulation of enterocyte extracellular Ca2+ influx.