Serotonin increases Na(+)-dependent Ca2+ efflux from bovine adrenal chromaffin cells in culture

5-hydroxytryptamine action in the rat olfactory bulb: In vitro electrophysiological patch-clamp recordings of juxtaglomerular and mitral cells

The olfactory bulb, first relay of olfactory pathways, is densely innervated by serotoninergic centrifugal fibers originating from the raphe nuclei. Although serotonin innervation was reported to be involved in olfactory learning in mammals, the action of this neurotransmitter on its putative cellular targets has been never described through unitary recordings. This lack of data initiated the present study where the effects of 5HT on juxtaglomerular and mitral cells are analyzed using whole-cell recordings on olfactory bulb slices. Serotonin depolarizes 34% of 525 JG cells. A multivariate statistical analysis of juxtaglomerular cells characteristics shows that the serotonin responsive cell group can be individualized regarding their tonic discharge-mode in response to a direct current injection, their lower expression of hyperpolarization-activated cation current and their low membrane capacities. The use of ion channel blockers and ramp voltage protocol indicate that serotoninergic depolarization of juxtaglomerular cells may be due to a nonselective cation current with a reversal potential of -44 mV. Pharmacological tests with serotonin receptor antagonists and agonists reveal that 5HT action on juxtaglomerular cells would be mainly mediated by 5HT2C receptors. In mitral cells, serotonin acts on 49.1% of the 242 tested cells, inducing two types of responses. A first subset of mitral cells (26.8%, n=65) were hyperpolarized by serotonin. This response would be indirect and mediated by action of GABA on GABAA receptors since it was antagonized by bicuculline. The involved GABAergic neurons are hypothesized to be juxtaglomerular and granular cells, on which serotonin would act mainly via 5HT2C and via 5HT2A receptors respectively. The second subset of mitral cells (22.3%, n=54) were directly depolarized by serotonin acting through 5HT2A receptors. Our data on serotonin action on juxtaglomerular cells and mitral cells reveal a part of functional mechanisms whereby serotonin can act on olfactory bulb network. This is expected to enrich the understanding of its determining role in olfactory learning.

Localization and role of serotonin in the adrenal gland of Podarcis sicula (Reptilia, Lacertidae)

The occurrence of serotonin (5-hydroxytryptamine; 5-HT) in the chromaffin cells of Podarcis sicula adrenal gland was demonstrated by immunocytochemical techniques: ABC and immunogold methods. At LM and EM levels, antiserum against 5-HT revealed serotonin immunoreactivity prevalently in noradrenalin (NA) cells, on and around secretory vesicles; adrenalin (A) cells appeared scarcely stained. The role of serotonin in the regulation of adrenal gland activity was studied in vivo using LM and EM techniques coupled to a specific radioimmunoassay for adrenocorticotropic hormone (ACTH) and corticosterone. 5-HT (0.7 mg/100 g body wt)/day for 4 days increased ACTH and corticosterone release; at LM and EM level clear signs of stimulation in the steroidogenic tissue were observed, as evidenced by the variations of lipid/cytoplasm ratio. In the chromaffin tissue, LM observations evidenced a variation of the numeric NA/A cell ratio; at EM level, chromaffin tissue showed intermediate cells with A, NA, and very clear granules with granular elements. The occurrence of these cells might be the result of a process of resynthesis following serotonin-stimulated catecholamine release. These data suggested that serotonin might be involved in the modulation of Podarcis pituitary-adrenal axis, and act as a paracrine factor to modulate corticosteroid production.

Stimulatory effect of enkephalins on calcium efflux from bovine adrenal chromaffin cells in culture

The effects of leucine- and methionine-enkephalin, opiate peptides, on Ca2+ efflux from cultured bovine adrenal chromaffin cells were examined. These enkephalins stimulated the efflux of 45Ca2+ from cells in a concentration-dependent manner (10(-8) M-10(-6) M). Leucine-enkephalin did not increase the intracellular free Ca2+ level, 45Ca2+ uptake, catecholamine secretion, cAMP level or cGMP level. The peptide-stimulated 45Ca2+ efflux was not inhibited by incubation in Ca2+-free medium, but was inhibited by incubation in Na+-free medium. These results indicate that enkephalins stimulate extracellular Na+-dependent 45Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably by stimulating membrane Na+/Ca2+ exchange.

The pulmonary neuroendocrine system and drainage of the fetal lung: effects of serotonin

The neuroendocrine system of the lungs is maximally developed and activated at birth, but has no clear function. Here, one of its products, serotonin, was tested for an ability to stop lung fluid production or activate reabsorption. Lungs from fetal guinea pigs (61 +/- 2 days of gestation) were supported in vitro for 3 h; lung liquid production was monitored by a dye dilution method. Initial studies on 36 young fetuses (61 +/- 1 days of gestation) showed that untreated controls produced fluid at 1.17 +/- 0.23 ml.kg-1.h-1, with no significant change over 3 h (ANOVA; regression analysis); those given 10(-8) M serotonin during the middle hour showed no significant changes, but those given 5 x 10(-8), 10(-7), 10(-6), or 10(-5) M serotonin reduced production significantly (P < 0.01 to P < 0.0005). Responses were linear up to 10(-7) M (threshold, 10(-9) M) and then become maximal at 50% reduction. However, responses increased with age. Comparison of 40 fetuses divided into groups of 60-61 or 65-67 days of gestation showed a large and significant increase in responses in the older fetuses (P < 0.01), where half the preparations reabsorbed fluid. Serotonin receptors were involved, since 10(-6) M cyproheptadine abolished responses (based on 24 preparations). Amiloride-sensitive Na+ channels were involved, since 10(-6) M amiloride abolished responses (based on 24 preparations). These results, in combination with earlier results from somatostatin and dopamine, together with histochemical and clinical observations, strongly suggest that the neuroendocrine system of the lungs may find a function in clearing fluid from the lungs at time of birth.

Endothelin-1 stimulates sodium-dependent calcium efflux from bovine adrenal chromaffin cells in culture

1. The effect of endothelin (ET)-1 on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. ET-1 (10(-7) M) significantly increased intracellular free Ca2+ level ([Ca2+]i), 45Ca2+ uptake and catecholamine secretion in the cells. 2. ET-1 stimulated the efflux of 45Ca2+ from the cells preloaded with 45Ca2+ in a concentration-dependent manner (10(-9)-10(-7) M). This stimulatory effect was inhibited by ET(B) receptor antagonist BQ788, but not by ET(A) receptor antagonist BQ123. Selective ET(B) receptor agonists Suc-[Glu9, Ala11.5]-ET-1 and sarafotoxin S6c (SRTX) also stimulated 45Ca2+ efflux from the cells. 3. ET-1, Suc-[Glu9 Ala11.15]-ET-1 and SRTX increased the level of cyclic GMP in the adrenal chromaffin cells. ET-1 induced an increase in the nitric oxide (NO) level in the cells. The stimulatory effects by which ET- increases NO level and 45Ca2+ efflux were inhibited by NG-monomethyl-L-arginine acetate (L-NMMA), a competitive inhibitor of NO synthase. 4. The 45Ca2+ efflux stimulated by ET-1 was inhibited by deprivation of extracellular Na+, but not by deprivation of Ca2+. 5. These results suggest that ET-1 stimulates an extracellular Na+-dependent Ca2+ efflux through the activation of NO synthase in cultured bovine adrenal chromaffin cells.