Search

To analyze the cross-reactivity between serotonin (5-HT) and histamine, the in vitro transcribed RNA for the 5-HT1c receptor was functionally expressed in Xenopus oocytes. 5-HT significantly increased 45Ca2+ efflux in RNA-injected oocytes, but not in uninjected and water-injected control oocytes. Furthermore, histamine and the H1 receptor agonists, but not the H2 and H3 agonists, significantly induced 45Ca2+ efflux in 5-HT1c receptor RNA-injected oocytes, but not in uninjected and water-injected oocytes. However, the H1, H2, and H3 antagonists failed to inhibit histamine-induced 45Ca2+ efflux at 10(-6) M. This finding suggests that the 5-HT1c receptor can be activated by both 5-HT and histamine, although the action of histamine is different from classic histamine pharmacology.

The rat substance P (SP) receptor cDNA has been transfected into cultured rat KNRK cells, and a stable cell line expressing functional SP receptors established. Upon stimulation with SP, these cells responded by simultaneously activating two signaling pathways: the mobilization of intracellular Ca2+ and the raising of cyclic adenosine triphosphate (cAMP) levels. Both Ca2+ and cAMP responses were elicited in a similar dose-dependent manner with half maximal concentrations of approximately 5 × 10−10 M. Following ionomycin treatment SP-dependent Ca2+ responses were abolished, whereas cAMP responses were preserved. Forskolin eliminated the SP-dependent cAMP elevation, however, the SP-induced Ca2+ mobilization remained unchanged. Furthermore, treatment with phorbol esters had no significant effect on either of the two SP-induced responses. Thus it appears that the SP receptor is capable of independently activating Ca2+ mobilization and cAMP pathways. These results may provide new insights for further understanding the diverse activities of SP in various systems in vitro and in vivo. © 1992 Wiley-Liss, Inc.

The mitogenic effect of corticotropin-releasing factor (CRF) on rat lymphocytes was investigated. When rat splenocytes were cultured for 48 hr with CFR, a dose-dependent increase in incorporation of 3H-thymidine (3H-Tdr) was observed, with a maximal response at 10 nM CRF. Comparison of the proliferative effect of CRF on enriched populations of B lymphocytes, T lymphocytes, or macrophages revealed that only B lymphocytes responded following treatment with CRF. When lymphocytes derived from different lymphoid tissues were compared, CRF had a greater proliferative effect on lymphocytes derived from gut-associated lymphoid tissue (mesenteric lymph nodes and Peyer's patches) than on lymphocytes from spleen or inguinal lymph nodes; CRF had no effect on thymocytes. Synthetic fragments of CRF were used to determine which portions of the peptide are recognized by lymphocytes. The C-terminal fragments alpha-helical CRF9-41 and CRF21-41 were as potent as native CRF in stimulating B-lymphocyte proliferation, whereas CRF1-20 did not stimulate proliferation. The activity of these peptides suggests that CRF stimulates lymphocyte proliferation by cellular recognition of structural determinants in the C-terminal one-half of the peptide.

Receptors for somatostatin (SOM) were identified on mouse bone marrow derived mast cells (MBMMC) and shown to vary in expression with the state of proliferation and differentiation of the MBMMC. Flow cytometric studies of the binding of fluorescein-labeled SOM and concurrent analyses of the binding of [125I]SOM demonstrated that the population of MBMMC capable of recognizing SOM specifically is that exhibiting a proliferative response to interleukin-3. The MBMMC that bound SOM reached a maximal number at 72 hr following the addition of interleukin-3, and were distributed principally in the G2/M phase of the cell cycle. SOM did not influence directly the proliferative responses of MBMMC to interleukin-3. The level of expression of SOM receptors thus may reflect the state of differentiation of mast cells, as well as determining the funcitonal sensitivity to the inhibitory effects of SOM.