p-chloromercuribenzoate causes Ca2+-dependent exocytotic catecholamine secretion from cultured bovine adrenal medullary cells

Gap junctions coordinate the propagation of glycogenolysis induced by norepinephrine in the pineal gland

Chemical and electrical synapses are the two major communication systems that permit cell-to-cell communication within the nervous system. Although most studies are focused on chemical synapses (glutamate, γ-aminobutyric acid, and other neurotransmitters), clearly both types of synapses interact and cooperate to allow the coordination of several cell functions within the nervous system. The pineal gland has limited independent axonal innervation and not every cell has access to nerve terminals. Thus, additional communication systems, such as gap junctions, have been postulated to coordinate metabolism and signaling. Using acutely isolated glands and dissociated cells, we found that gap junctions spread glycogenolytic signals from cells containing adrenoreceptors to the entire gland lacking these receptors. Our data using glycogen and lactate quantification, electrical stimulation, and high-performance liquid chromatography with electrochemical detection, demonstrate that gap junctional communication between cells of the rat pineal gland allows cell-to-cell propagation of norepinephrine-induced signal that promotes glycogenolysis throughout the entire gland. Thus, the interplay of both synapses is essential for coordinating glycogen metabolism and lactate production in the pineal gland.

Insect diapause-specific peptide from the leaf beetle has consensus with a putative iridovirus peptide

Diapause and hibernation during periods of environmental adversity are essential features of the life cycle in many organisms, yet the molecular basis for these events differs among animals. We have identified an endogenous diapause/hibernation-specific peptide, from the leaf beetle Gastrophysa atrocyanea. This peptide provides antifungal activity, acts as a N-type voltage-gated Ca2+ channel blocker, and has a new consensus sequence with an unknown polypeptide encoded in the insect iridescent virus. These results indicate that the diapause-specific peptide may be utilized as a probe to analyze and compare functional and evolutional aspects of the life cycles of insects and iridoviruses.

Inhibition by pregnenolone sulfate of nicotinic acetylcholine response in adrenal chromaffin cells

To evaluate whether pregnenolone sulfate, an abundant neurosteroid in the brain, modulates nicotinic receptor-mediated responses, the effect of pregnenolone sulfate on acetylcholine-induced catecholamine secretion was investigated in cultured bovine adrenal chromaffin cells. Pregnenolone sulfate inhibited acetylcholine-induced catecholamine secretion (IC(50): 27 microM). In addition, pregnenolone sulfate inhibited acetylcholine-induced Na(+) (IC(50): 12 microM) and Ca(2+) (IC(50): 20 microM) influxes. However, pregnenolone sulfate did not inhibit either catecholamine secretion or Ca(2+) influx stimulated by high K(+). Binding of [3H]nicotine to nicotinic receptors was not altered by pregnenolone sulfate. The inhibitory effect on the acetylcholine-induced secretion was insurmountable by increasing acetylcholine concentrations, but was enhanced by decreasing external Na(+) concentrations. These results suggest strongly that pregnenolone sulfate noncompetitively inhibits nicotinic receptor-operated ion channels, thereby suppressing Na(+) influx through the channels and, consequently, attenuates both Ca(2+) influx and catecholamine secretion. Our results further indicate that pregnenolone sulfate may modulate nicotinic receptor-mediated responses in the brain.

Transbilayer transport of a propyltrimethylammonium derivative of diphenylhexatriene (TMAP-DPH) in bovine blood platelets and adrenal chromaffin cells

The membrane fluorescent probe N-((4-(6-phenyl-1,3,5-hexatrienyl)phenyl)propyl)trimethylammonium (TMAP-DPH) has an additional three-carbon spacer between the fluorophore and the trimethylammonium substituent of 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). As a basic study to clarify the transport mechanism of amphiphilic quaternary ammoniums, we observed the characteristics of the transbilayer transport of TMAP-DPH in bovine blood platelets and bovine adrenal chromaffin cells using the albumin extraction method. We compared these inward transport rates with those of TMA-DPH. TMAP-DPH crossed into the cytoplasmic layers of the membranes more slowly than TMA-DPH after rapid binding to the outer halves of the plasma membranes. The transport rate markedly depended on temperature. Time to reach the half-maximal incorporated amount of TMAP-DPH increased threefold accompanied by an increase in the concentration from 0.2 to 1.5 microM. The transport was stimulated significantly by various types of membrane perturbations such as modification of sulfhydryl-groups by N-ethylmaleimide and benzyl alcohol-induced increase in the fluidity of the lipid bilayer. The saturation phenomenon suggested the presence of the regulatory process in the transbilayer transport of TMAP-DPH.

Involvement of Hg2+-sensitive sulfhydryl groups in regulating noradrenaline release induced by S-nitrosocysteine in rat brain slices

Nitric oxide has been shown to regulate neurotransmitter release. Previously, we reported that S-nitrosothiols such as S-nitrosocysteine (SNC) stimulate noradrenaline (NA) release in rat hippocampus in vivo and in vitro. To examine the role of sulfhydryl groups in SNC-induced NA release, the effects of metal ions such as Hg2+ and N-ethylmaleimide (NEM, a sulfhydryl alkylating agent) on [3H]NA release from labeled rat brain slices (hippocampus and cerebral cortex) were studied and compared with the effects of SNC. The addition of 200 microM HgCl2, but not Pb2+, Zn2+, or Cd2+, stimulated [3H]NA release from both types of slices in the presence of extracellular CaCl2. p-Chloromercuribenzoic acid (p-CMBA) also stimulated [3H]NA release. NEM stimulated [3H]NA release from both types of slices in the presence and absence of extracellular CaCl2. The effect of 200 microM NEM was enhanced, but the effect of 200 microM SNC was inhibited by co-addition of 200 microM p-CMBA in the absence of extracellular CaCl2. The concentration-response curve of SNC shifted to the right after co-addition of 200 microM p-CMBA or 100 microM HgCl2, although the effect of 200 microM NEM was additive to the effect of SNC. These findings demonstrate that SNC acts as a sulfhydryl agent on proteins that regulate NA release, and that SNC may share the same sulfhydryl groups with Hg compounds. The effect of T-588 ¿(R)-(-)-(benzo[b]thiophen-5-yl)-2-[2-(N,N-diethylamino)ethoxy]eth anol hydrochloride¿, a novel cognitive enhancer and a stimulator of NA release, was compared with the effects of sulfhydryl reagents.

Asymmetrical membrane fluidity of bovine adrenal chromaffin cells and granules and effect of trichosporin-B-VIa

We examined membrane fluidity of bovine adrenal chromaffin cells and chromaffin granules using cationic trimethylammonium derivative of diphenylhexatriene (TMA-DPH) as a fluorescence probe. After adding TMA-DPH to the suspension of chromaffin cells and that of granules, it first bound to the outer layer of the plasma membrane of the cells and that of the granule membrane, then gradually penetrated the inner layer of each membrane and distributed to both leaflets of the respective membranes. Accompanying increases in the ratio of incorporated probe on the cytoplasmic side of the chromaffin cell membrane, its fluorescence anisotropy gradually decreased. However, in chromaffin granules, the fluorescence anisotropy gradually increased with increases in the ratio of incorporated probe. These findings suggest that the inner layer of the plasma membrane and outer layer of the granular membrane are more fluid than the corresponding side of each membrane, which is suitable for the fusion between both membranes. We also examined the effect of trichosporin-B-VIa, a fungal ion channel forming alpha-aminoisobutyric acid-containing peptide, on the fluidity of chromaffin cells using TMA-DPH. The peptide decreased the fluorescence anisotropy and increased the fluorescence intensity in the concentration range that induced Ca2+ dependent catecholamine secretion, suggesting that a change in lipid dynamics of the lipid bilayer of the plasma membrane was induced by this peptide.

Properties of ginseng saponin inhibition of catecholamine secretion in bovine adrenal chromaffin cells

To investigate the relationship between the inhibitory effects of ginseng saponins (ginsenosides) on acetylcholine-evoked secretion of catecholamines and the structures of ginsenosides, we examined the effects of ginsenoside-Rg3 and -Rh2, which are panaxadiol saponins, 20(R)- and 20(S)-ginsenoside-Rg2, which are epimers involving the hydroxyl group at C-20 of sapogenin, and other plant saponins on the acetylcholine-evoked secretion of catecholamines from cultured bovine adrenal chromaffin cells. The ginsenoside-Rg3 (1-100 microM) and -Rh2 (10-100 microM) greatly reduced the acetylcholine-evoked secretion in a concentration-dependent manner comparable to that of ginsenoside-Rg2, a panaxatriol saponin, which was the most potent inhibitor in our previous study. 20(R)- and 20(S)-ginsenoside-Rg2 (1-100 microM) similarly reduced the acetylcholine-evoked secretion. In contrast, saikosaponin-a, glycyrrhizin and the cardiac glycosides (100 nM-100 microM), digitoxin and digoxin, had no significant inhibitory effect on catecholamine secretion. Saikosaponin-c (10-100 microM), however, had an inhibitory effect, which was less than that of ginsenoside-Rg2 and -Rg3. These results strongly suggest that the inhibitory effects of ginsenosides on the acetylcholine-evoked secretion of catecholamines from bovine adrenal chromaffin cells are a unique property of ginseng. Further, the relationship between the inhibitory effects and the structures of ginsenosides is discussed.

Role of the Gln/Glu residues of trichocellins A-II/B-II in ion-channel formation in lipid membranes and catecholamine secretion from chromaffin cells

Trichocellins (TC) A-II and B-II, 20-residue peptaibols isolated from conidia of the fungus Trichoderma viride, have the same sequence except for the residue at position 18. Both TCs were found to form voltage-dependent ion-channels in bilayer lipid membranes (BLM) and to induce catecholamine secretion from bovine adrenal chromaffin cells through Ca2+ influx. TC-A-II (Gln18, neutral) was more effective than TC-B-II (Glu18, charged) for macroscopic current induction in BLMs and for catecholamine secretion from chromaffin cells, suggesting that Glu18 is unfavorable for the ion-channel formation in BLMs and chromaffin cell membranes. Nevertheless, single-channel recordings indicated that TC-B-II forms larger pores with longer open lifetimes than those of TC-A-II. This indicates that the negatively charged carboxyl group of Glu at position 18 stabilizes larger pores. The effects of the negative charge of Glu18 on the activities were confirmed by the use of a TC-B-II analog containing the methyl ester of Glu18.

Role of proline residue in the channel-forming and catecholamine-releasing activities of the peptaibol, trichosporin-B-VIa

Trichosporin-B-VIa (TS-B-VIa) has a Pro14-kinked helical structure which is considered to be important for the formation of peptaibol-type ion-channels in lipid bilayer membranes. TS-B-VIa and its analog [Aib14]TS-B-VIa with Pro-->Aib substitution at position 14, resulting in a straight helical structure, were tested for ion-channel-forming activity in planar lipid bilayer membranes and for ability to induce catecholamine secretion from cultured bovine adrenal chromaffin cells. Voltage-dependent multi-channel conductance, which is characteristic of TS-B-VIa, was also observed for [Aib14]TS-B-VIa. In single-channel measurements, current fluctuations induced by [Aib14]TS-B-VIa had a shorter life-time and showed fewer substates than those induced by TS-B-VIa. Catecholamine secretion induced by these peptides at low concentrations is completely Ca(2+)-dependent. At high concentrations, TS-B-VIa-induced secretion was partly independent of external Ca2+, but this was not the case for the analog. The differences of behavior can be explained in terms of the differences of hydrophobicity, and magnitude of dipole moment due to the conformational changes around position 14 and the C-terminal domain caused by the Pro-->Aib substitution.

Pertussis toxin pretreatment enhances catecholamine secretion induced by pituitary adenylate cyclase-activating polypeptide in cultured porcine adrenal medullary chromaffin cells: a possible role of the inositol lipid cascade

We determined how pertussis toxin (PTX) pretreatment alters PACAP-induced catecholamine secretion in cultured porcine adrenal medullary cells. Pretreatment of these cells with PTX (1 ng/ml for 24 h or 10 ng/ml for 6 h) markedly enhanced PACAP-induced catecholamine secretion. PTX pretreatment also produced a small increase in basal secretion and secretion in response to nicotine and carbachol, but the effect of the PACAP-induced secretion was most striking. We examined the role of the phosphoinositol cascade in potentiating the PACAP-induced catecholamine secretion by PTX and found that PACAP-induced accumulation of inositol phosphates in PTX-pretreated cells was significantly greater than that in untreated cells. Furthermore, removal of extracellular Ca2+ and addition of Ca2+ channel blockers inhibited the catecholamine secretion induced by PACAP in PTX-pretreated cells. From these results, we speculate that a PTX-sensitive G-protein tonically inhibits phospholipase C. PTX enhances the PACAP-induced secretion of catecholamine by blocking the action of this inhibitory G-protein.

Effects of SK&F 96365, an inhibitor of receptor-mediated Ca2+ entry, on Ca2+ influx and catecholamine secretion in bovine adrenal chromaffin cells

SK&F 96365 (1-[3-(4-methoxyphenyl)propoxyl]-1-(4-methoxyphenyl)ethyl-1H- imidazole HCl) (1-50 microM), an inhibitor of receptor-mediated Ca2+ entry, reduced both acetylcholine (ACh)- and 56 mM K+ (high K+)-induced 45Ca2+ influxes and catecholamine secretion in bovine adrenal chromaffin cells. However, SK&F 96365 at lower concentrations (1-3 microM) inhibited only ACh-induced 45Ca2+ influx and secretion but not their high K(+)-induction. In Na(+)-free medium, ACh-induced 45Ca2+ influx and secretion were also considerably decreased by SK&F 96365 at low concentrations (1-3 microM). These results suggest that in the chromaffin cells, not only voltage-sensitive calcium channels but also ACh receptor-operated calcium channels at least in part contribute to the influx of Ca2+ which triggers the catecholamine secretion from the cells when the cells are exposed by ACh.

Cisplatin, an antineoplastic drug, inhibits catecholamine secretion from bovine adrenal chromaffin cells

Long-term pretreatment (12-120 h) of cultured bovine adrenal chromaffin cells with cis-diamminedichloroplatinum (cisplatin, Pt(NH3)2Cl2) (33 microM), an antineoplastic drug, resulted in a decrease in the secretion of catecholamines from the cells stimulated by acetylcholine. Acetylcholine-induced 45Ca2+ influx into the cells was also reduced in the cells pretreated with cisplatin for 48 h. The concentration-response curves (3-66 microM) for cisplatin inhibition of the secretion and 45Ca2+ influx were quite similar. Pretreatment of cells with 33 microM Pt4+ or carboplatin, an analog of cisplatin, for 48 h also led to a decrease in acetylcholine-evoked secretion, but not with 33 microM Pt2+ or other metals (Au+, Au3+, Ni2+, Os3+, Pd2+, Ir3+, and Ir4+) that have properties similar to Pt4+. These results strongly suggest that in bovine adrenal chromaffin cells, cisplatin (3-66 microM) inhibits catecholamine secretion by the suppression of the Ca2+ influx into the cells evoked by acetylcholine and that the inhibitory effect of cisplatin is attributable to the tetravalent platinum ion in its molecule.

Role of Ca2+/phospholipid-dependent protein kinase in catecholamine secretion from bovine adrenal medullary chromaffin cells

The role of Ca2+/phospholipid-dependent protein kinase (protein kinase C) in catecholamine secretion from bovine adrenal medullary chromaffin cells was examined using four protein kinase C inhibitors: polymyxin B, sphingosine, staurosporine, and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7). For this purpose, digitonin-permeabilized chromaffin cells were used. Secretion of catecholamines from these cells was stimulated by the addition of micromolar amounts of exogenous free Ca2+. 12-O-Tetradecanoylphorbol-13-acetate (TPA) and arachidonic acid, activators of protein kinase C, enhanced the catecholamine secretion evoked by Ca2+. But phorbol-12, 13-diacetate, a phorbol ester analog that does not activate protein kinase C, had no effect on Ca2(+)-evoked secretion. Polymyxin B at a low concentration (1 microM) abolished the enhancement of secretion by TPA or arachidonic acid without affecting the secretion evoked by Ca2+. However, polymyxin B at higher concentrations (10-100 microM) greatly reduced Ca2+-evoked catecholamine secretion. Sphingosine 10 microM-1 mM), Staurosporine (100 nM-1 microM, and H-7 (100-500 microM) inhibited TPA- or arachidonic acid-enhanced secretion but not Ca2(+)-evoked secretion. In cells in which protein kinase C was down-regulated by TPA, specific binding of [3H]phorbol-12,13-dibutyrate to the cells almost disappeared and the enhancement of secretion by TPA was no longer observed, whereas Ca2(+)-evoked secretion was maintained. These results strongly suggest that protein kinase C is not essential for the Ca2(+)-dependent catecholamine secretion from bovine adrenal chromaffin cells, but acts instead as a modulator.

Preferential release of neuroactive amino acids from the ventrolateral medulla of the rat in vivo as measured by microdialysis

The basal overflow of extracellular endogenous amino acids was measured from the ventrolateral medulla of urethane anaesthetized rats in vivo by microdialysis. Inclusion of a mercury salt, p-chloromercuriphenylsulphonic acid, in the dialysate (Krebs' solution), results in a preferential increase in the overflow of aspartate, glutamate, glycine and GABA. A smaller increase in the overflow of the glutamate precursor and metabolite, glutamine, was also found. There was no significant change in the basal extracellular levels of taurine, asparagine, alanine, serine, ornithine or lysine. Inclusion of a specific GABA uptake inhibitor, nipecotic acid, in the dialysate results in an immediate, dose dependent increase in the overflow of GABA, and to a lesser extent, taurine. Since it is likely that mercury salts increase neurotransmitter release by increasing free intracellular calcium ion concentrations, it is suggested that these results provide further evidence for a physiologically relevant neurotransmitter role for aspartate, glutamate, glycine and GABA in the ventrolateral medulla.