CA-2+ RELEASE AND INSP3 PRODUCTION IN AVIAN UTERINE CELLS - EFFECTS OF PGF2-ALPHA AND AVT

Primary cultures of smooth muscle cells isolated from the shell gland ("uterus") of the domestic hen were permeabilized with digitonin and loaded with (Ca2+)-Ca-45 in the presence of ATP. When these cells were stimulated with prostaglandin F2-alpha (PGF2-alpha), arginine vasotocin (AVT), or D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], there was a rapid, biphasic, and dose-related release of (Ca2+)-Ca-45 from nonmitochondrial pools. 2-Nitro-4-carboxyphenyl-N,N-diphenylcarbamate, an inhibitor of phospholipase C, had no effect on PGF2-alpha- and Ins(1,4,5)P3-promoted (Ca2+)-Ca-45 efflux, whereas it significantly inhibited AVT-stimulated and a stable analogue of GTP-stimulated (Ca2+)-Ca-45 release. In fura-2-loaded intact cells, both PGF2-alpha and AVT increased intracellular CA2+ levels ([Ca2+]i) in a dose-related manner in the presence of extracellular Ca2+. However, omission of extracellular Ca2+ prevented a PGF2-alpha, but not AVT-induced, rise in [Ca2+]i. In D-myo-[H-3]inositol-labeled cells, 10 nM AVT caused a rapid, two- to threefold increase in ]H-3[-InsP3, whereas PGF2-alpha up to 1-mu-M was ineffective. Raising PGF2-alpha to 10-mu-M increased total inositol phosphates by 22% over controls (P < 0.05). These results point to marked differences in the mechanisms by which AVT and PGF2-alpha regulate ]Ca2+[i in uterine smooth muscle cells. It is suggested that the two agonists act in concert to initiate oviposition.