Effects of opioid compounds on basal and muscarinic induced accumulation of inositol phosphates in cultured bovine chromaffin cells

Histamine-stimulated phospholipase C signalling in the adrenal chromaffin cell: effects on inositol phospholipid metabolism and tyrosine hydroxylase phosphorylation

1. The present report gives a detailed account of histamine-stimulated phospholipase C (PLC) activity in bovine adrenal chromaffin cells. 2. Histamine activation of H1 receptors stimulates PLC with a biphasic sensitivity to extracellular Ca2+. The initial response (the first 15 s stimulation) was not reduced by the removal of extracellular Ca2+, whereas the maintenance of PLC activity beyond this time required Ca2+ influx. 3. Phospholipase C activity in response to a 10 min incubation with histamine was inhibited by La3+ (3 mmol/L) or SKF96365 (10 mumol/L). Nifedipine (10 mumol/L), but not omega-agatoxin IVA (100 nmol/L) or omega-conotoxin GVIA (300 nmol/L), produced a partial inhibition of PLC activity. The response was also partially inhibited by a reduction in the extracellular Cl- concentration (40 mmol/L) or by the inclusion of the Cl- channel blocker N-phenylanthranilic acid (300 mumol/L). 4. Kinetic analysis of the rate of turnover of the various inositol phosphate isomers in response to histamine suggested that the inositol monophosphates were being produced from a source in addition to inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) metabolism. This conclusion was supported by the differential action of pertussis toxin and neomycin on Ins(1,4,5)P3 formation compared with inositol monophosphate formation. 5. We have attempted to identify a defined role for the intracellular Ca2+ mobilized in these cells in response to histamine. After short incubations (up to 3 min), histamine was able to regulate the site-specific phosphorylation of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis. This observation has important implications for a possible role for the PLC signalling pathway in controlling the rate of catecholamine biosynthesis.

Staurosporine inhibits inositol phosphate formation in bovine adrenal medullary cells

The effect of protein kinase C activators and inhibitors on histamine-stimulated phospholipase C in bovine adrenal medullary cells has been investigated. The protein kinase C activators, phorbol 12,13-dibutyrate (PDB) or sn-1,2-dioctanoylglycerol (DOG), inhibited histamine-stimulation of phospholipase C. This inhibition was prevented by the protein kinase C-selective inhibitor Ro 31-8220 (3-[1-[3-(2-isothioureido) propyl]indol-3-yl]-4-(1-methylindol-3-yl)-3-pyrrolin-2,5-dio ne) but not the broad spectrum protein kinase inhibitor staurosporine. Indeed staurosporine on its own inhibited both the histamine-stimulated response and, in permeabilized cells, phospholipase C activated by Ca2+. Staurosporine inhibition of phospholipase C is unlikely to be mediated via protein kinase A or Ca2+/calmodulin-dependent protein kinase because it was not reproduced by selective inhibition of these kinases. Staurosporine treatment, however, reduced inositol phospholipid levels in stimulated cells. Thus staurosporine and Ro 31-8220, two widely used protein kinase C inhibitors, have quite different effects on phospholipase C activation. Furthermore, staurosporine may cause this inhibition through a reduction in the level of phospholipase C substrate.

LiCl uncouples signal transduction in morphine-induced supraspinal antinociception in mice

1. The present study examined whether LiCl antagonism of morphine-induced antinociception in mice occurs at mu-opioid receptors. 2. The antinociceptive ED50 value of intracerebroventricular morphine was maximally increased compared to controls 18 hr after LiCl (10 mmol/kg, s.c.) and remained significantly less (P < 0.05) 7 and 14 days after once-daily LiCl treatment. 3. There was no significant difference in [3H]-[D-Ala2,N-MePhe4,Gly- ol5]enkephalin affinity or receptor density compared to controls (KD = 0.43 nM, Bmax = 54.8 +/- 9.3 pM). 4. These results suggest that LiCl's effect is not on mu-opioid receptors, but rather on some distal site.

Mu-opioids activate phospholipase C in SH-SY5Y human neuroblastoma cells via calcium-channel opening

We have recently reported that, in SH-SY5Y cells, mu-opioid receptor occupancy activates phospholipase C via a pertussis toxin-sensitive G-protein. In the present study we have further characterized the mechanisms involved in this process. Fentanyl (0.1 microM) caused a monophasic increase in inositol 1,4,5-trisphosphate mass formation, with a peak (20.5 +/- 3.6 pmol/mg of protein) at 15 s. Incubation in Ca(2+)-free buffer abolished this response, while Ca2+ replacement 1 min later restored the stimulation of inositol 1,4,5-trisphosphate formation (20.1 +/- 0.6 pmol/mg of protein). In addition, nifedipine (1 nM-0.1 mM), an L-type Ca(2+)-channel antagonist, caused a dose-dependent inhibition of inositol 1,4,5-trisphosphate formation, with an IC50 of 60.3 +/- 1.1 nM. Elevation of endogenous beta/gamma subunits by selective activation of delta-opioid and alpha 2 adrenoceptors failed to stimulate phospholipase C. Fentanyl also caused a dose-dependent (EC50 of 16.2 +/- 1.0 nM), additive enhancement of carbachol-induced inositol 1,4,5-trisphosphate formation. In summary, we have demonstrated that in SH-SY5Y cells activation of the mu-opioid receptor allows Ca2+ influx to activate phospholipase C. However, the possible role of this mechanism in the process of analgesia remains to be elucidated.

The sigma compounds 1,3-di-o-tolylguanidine and N-allylnormetazocine inhibit agonist-stimulated inositol phospholipid metabolism in bovine adrenal medullary cells

Muscarine stimulated a concentration-dependent accumulation of [3H]inositol phosphates in bovine adrenal medullary cells preloaded with [3H]inositol. This muscarinic activation of inositol phospholipid metabolism was fully inhibited by the sigma-ligand 1,3-di-o-tolylguanidine (DTG) with an IC50 of approximately 45 microM. Higher concentrations (100 microM) of (+) N-allylnormetazocine (SKF-10047) also partially inhibited this response. A concentration of DTG sufficient to fully inhibit the muscarinic response also produced a significant partial inhibition of [3H]inositol phosphate accumulation in response to histamine but not to angiotensin II. These data demonstrate that sigma-compounds inhibit agonist-stimulated inositol phospholipid metabolism in bovine adrenal medullary cells, with a degree of selectivity towards the muscarinic response.

Non-cholinergic nervous control of catecholamine secretion from perfused bovine adrenal glands

1. Field stimulation of adrenal nerves was used to study nervous control of adrenal catecholamine secretion in isolated, retrogradely perfused, bovine adrenal glands. 2. Secretion of both adrenaline and noradrenaline was maximal at 10 Hz. Secretion at 2 Hz was < 10% of maximum. Stimulating with trains of pulses at ten times the average frequency for 1 s out of every 10 s gave 2-fold greater secretion at 2 Hz average frequency, similar release at 5 Hz, and only half the secretion at 10 Hz, compared to continuous stimulation at the average frequency. 3. At 10 Hz, adrenaline and noradrenaline secretion was virtually abolished by tetrodotoxin (1 microM), but was only reduced by 75% by prolonged perfusion with a combination of mecamylamine (5 microM) and atropine (1 microM). Mecamylamine and atropine completely abolished the secretory response to 2 Hz stimulation. Tetrodotoxin had no significant effect on secretion induced by perfusing glands with nicotine (5 microM), while mecamylamine abolished this response. Mecamylamine and atropine had no effect on secretion induced by K+ depolarization. 4. The secretion of adrenaline and noradrenaline induced by 10 Hz stimulation was not inhibited by naloxone at either 1 or 30 microM. 5. The results suggest that bovine adrenal chromaffin cells, like those in the rat, receive a significant non-cholinergic secretomotor innervation. In contrast to the rat, however, the non-cholinergic component in the bovine adrenal is negligible at low-frequency nerve stimulation and substantial at higher frequencies, and is not antagonized by naloxone. The identity of the non-cholinergic transmitter remains to be determined.

The modulation of placental lactogen release by opioids: a role for extracellular calcium

We previously reported that kappa opioids stimulated the release of human placental lactogen (hPL) from trophoblastic cells and that this effect was prevented by co-incubation with naloxone. We also reported that adenylate cyclase was not directly involved in this process. In order to understand the post-receptor events mediating hPL release by opioids in the human placenta, we studied the role of extracellular calcium. Human trophoblastic cells obtained by trypsin digestion were cultured for 48 h in Ham's F-10 medium supplemented with 10% fetal bovine serum (FBS), 200 U/ml penicillin, and 200 micrograms/ml streptomycin. 45Ca2+ influx was then measured by filtration on glass-fiber filters. We observed a time- and dose-dependent stimulation of 45Ca2+ influx by ethylketocyclazocine (EKC) with an EC50 of 0.5 nM and a maximal stimulation of 196% over control. This effect was completely blocked by naloxone, a non-specific opioid antagonist, and by nor-binaltorphimine, a specific kappa antagonist. We also demonstrated that U-50,488 (kappa agonist) had the same stimulatory effect as EKC (221 +/- 25% of control). D-Ala2,NMe-Phe4,Gly-ol5)-enkephalin (DAGO) (mu agonist) slightly stimulated Ca2+ influx (128 +/- 5% of control, p > 0.05) whereas D-Ser2,Leu,Thr6)-enkephalin (DSLET) (delta agonist) had no effect. Pre-incubation of trophoblastic cells with pertussis toxin (PTX) did not affect the EKC-induced 45Ca2+ influx, suggesting that this placental opiate effect is not coupled with PTX-sensitive G proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscarinic acetylcholine receptor enhances phosphatidylcholine hydrolysis via phospholipase D in bovine chromaffin cells in culture

Although it is well-established that inositol-containing lipids serve as precursors of intracellular second messenger molecules in chromaffin cells, we describe some findings that show the formation of diacylglycerol from phosphatidylcholine in response to agonist-mediated stimulation. Stimulation of chromaffin cells by acetylcholine produced a high turnover of phosphatidylcholine, as suggested by the release of [3H]choline derived from [3H]-phosphatidylcholine in experiments performed with [3H]choline chloride-prelabeled cells. An enhanced breakdown of phosphatidylcholine was also inferred from the finding of an increased formation of [3H]diacylglycerol in chromaffin cells prelabeled with [3H]glycerol. The diacylglycerol mass that accumulated after stimulation showed a distinct temporal course and seemed to exceed the mass that has been reported to be derived from phosphatidylinositol. In keeping with the purported origin from phosphatidylcholine, diacylglycerol showed a high content in [3H]oleate molecular species. Phospholipase D activity measurements and experiments performed in the presence of propranolol (an inhibitor of phosphatidic acid:phosphohydrolase) suggested that phosphatidylcholine is hydrolyzed by a phospholipase D activity, producing phosphatidic acid, which is subsequently degraded to diacylglycerol, rather than by a phospholipase C. Incubation of chromaffin cells in the presence of atropine before addition of acetylcholine showed complete inhibition of the increased formation of [3H]-diacylglycerol, whereas d-tubocurarine failed to do so. Taken together, these results suggest that acetylcholine activates phosphatidylcholine breakdown and diacylglycerol formation in chromaffin cells via a muscarinic-type receptor.

Opioid inhibition of nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells

The ability of a number of opioid agonists and antagonists to affect nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells has been investigated. High (10 microM) concentrations of the opioid agonist bremazocine produced a significant inhibition of nicotine-induced 45Ca2(+)-uptake throughout the 15 min time course examined. The opioid subtype-selectivity of this inhibition was investigated; mu and delta selective agonists produced only minor effects whereas the kappa selective agonist U50-488H and the endogenous opioid peptides dynorphin(1-13) and metorphamide almost abolished nicotine-induced 45Ca2(+)-uptake. The U50-488H inhibition was significant at 10 nM concentrations with an IC50 of approximately 1 microM. U50-488H inhibition could not be reversed or reduced by the opioid antagonists naxolone, diprenophine or Mr2266. Furthermore, Mr2266 and its optical isomer Mr2267 also produced marked inhibition of 45Ca2(+)-uptake. The inhibition was specific to nicotine-induced 45Ca2(+)-uptake in that a similar level of uptake evoked by potassium depolarization was unaffected by high concentrations of U50-488H. These data indicate that opioid inhibition of nicotine-induced 45Ca2(+)-uptake does not involve classical, stereospecific opioid receptors and suggests the involvement of a pharmacologically distinct opioid recognition site. It is speculated that this may be associated with the nicotine receptor-ionophore complex.

Opioid receptor-coupled second messenger systems

Although pharmacological data provide strong evidence for different types of opioid receptors (e.g., mu, delta, and kappa), they share many common properties in their ability to couple to second messenger systems. All opioid receptor types are coupled to G-proteins, since agonist binding is diminished by guanine nucleotides and agonist-stimulated GTPase activity has been identified in several preparations. Moreover, all three types inhibit adenylyl cyclase. This second messenger system has been identified for opioid receptors in both isolated brain membranes and in transformed cell culture. Studies with chronic treatment with opioid agonists suggest that the coupling of receptors with G-proteins and second messenger effectors may play important roles in development of opioid tolerance.

Substance P increases catecholamine secretion from perfused rat adrenal glands evoked by prolonged field stimulation

1. We have studied the effect of substance P (SP) on catecholamine (CA) secretion evoked by prolonged field stimulation from the perfused rat adrenal gland in vitro. 2. Previous studies show that SP has an inhibitory effect on the nicotinic response in a number of different tissue preparations. In the present study, we found that SP at concentrations from 10(-7) to 10(-6) M markedly increased CA secretion evoked by prolonged high-frequency field stimulation but not that evoked by low-frequency field stimulation. 3. In the absence of field stimulation SP by itself had no direct effect on CA secretion. This indicates that SP acts as a neuromodulator rather than a neurotransmitter to increase CA secretion from the adrenal medulla. 4. The nicotinic receptors were still functional following a period of prolonged field stimulation (120 min) because CA secretion was markedly increased in response to the nicotinic agonist dimethylphenylpiperazinium (DMPP). 5. Capsaicin pre-treatment reduced CA secretion evoked by prolonged field stimulation and the facilitatory action of SP on CA secretion lasted longer in these capsaicin-pre-treated rats than in controls, indicating that SP-containing capsaicin-sensitive fibres innervating the adrenal medulla may be involved in the regulation of CA secretion. 6. In parallel with the increase in CA secretion, 3H overflow from the splanchnic nerve pre-labelled with [3H]choline was also increased by SP. The increase in CA secretion by SP lasted longer than the increase in 3H overflow. These results suggest that SP facilitates CA secretion from the adrenal gland at two levels: (1) pre-synaptically by facilitating ACh release from splanchnic nerve terminals, and (2) post-synaptically by modulating the nicotinic secretory response by protection against nicotinic desensitization of secretion. 7. The present studies provide further evidence that endogenous SP in the splanchnic nerve may modulate CA secretion during stress.

Receptor stimulated formation of inositol phosphates in cultures of bovine adrenal medullary cells: the effects of bradykinin, bombesin and neurotensin

The ability of a number of drugs and neuropeptides to stimulate phosphoinositide metabolism in cultured bovine adrenal medullary cells has been assessed. Low concentrations (10 nM) of angiotensin II, bradykinin, histamine, arginine-vasopressin, and bombesin, and high (10 microM) concentrations of oxytocin, prostaglandins E1, and E2, beta-endorphin, and neurotensin stimulated significant accumulation of [3H]inositol phosphates in adrenal medullary cells preloaded with [3H)]inositol. Bradykinin stimulated a significant response at concentration as low as 10pM, with an EC50 of approximately 0.5 nM. The response was markedly inhibited by the bradykinin B2 antagonist [Thi5,8,D-Phe7] bradykinin but not the B1 antagonist [Des-Arg9,Leu8] bradykinin. Higher concentrations of bombesin and neurotensin were required to elicit a response (10 nM and 10 microM respectively). The bombesin response was sensitive to inhibition by the bombesin antagonist [D-Arg1,D-Pro2,D-Trp7,9Leu11]-substance P. In contrast, the neurotensin response was not reduced by the NT1 antagonist [D-Trp11]-neurotensin. These results indicate there are a number of agents that can stimulate phosphatidylinositide hydrolysis in the adrenal medullary cells by acting on different classes of receptors. Such a range of diverse agonists that stimulate inositol phosphate formation will facilitate further analysis of the phosphatidylinositide breakdown in chromaffin cell function.

Kappa opioid receptors stimulate phosphoinositide turnover in rat brain

The effects of various subtype-selective opioid agonists and antagonists on the phosphoinositide (PI) turnover response were investigated in the rat brain. The kappa-agonists U-50,488H and ketocyclazocine produced a concentration-dependent increase in the accumulation of IP's in hippocampal slices. The other kappa-agonists Dynorphin-A (1-13) amide, and its protected analog D[Ala]2-dynorphin-A (1-13) amide also produced a significant increase in the formation of [3H]-IP's, whereas the mu-selective agonists [D-Ala2-N-Me-Phe4-Gly5-ol]-enkephalin and morphine and the delta-selective agonist [D-Pen2,5]-enkephalin were ineffective. The increase in IP's formation elicited by U-50,488H was partially antagonized by naloxone and more completely antagonized by the kappa-selective antagonists nor-binaltorphimine and MR 2266. The formation of IP's induced by U-50,488H varies with the regions of the brain used, being highest in hippocampus and amygdala, and lowest in striatum and pons-medulla. The results indicate that brain kappa- but neither mu- nor delta-receptors are coupled to the PI turnover response.

Effects of phorbol esters and forskolin on basal and histamine-induced accumulation of inositol phosphates in cultured bovine adrenal chromaffin cells

The effect of phorbol esters and forskolin pretreatment on basal and histamine-induced accumulation of inositol phosphates and catecholamine release was examined in cultures of bovine adrenal chromaffin cells. Histamine caused a dose-dependent, Ca2+-dependent accumulation of total inositol phosphates with an EC50 at approximately 1 microM and an eight- to 10-fold increase at 100 microM within 30 min of incubation. Histamine (10 microM) also caused the release of cellular catecholamines amounting to some 2.8% of cellular stores released over a 20-min period. Both the inositol phosphate and catecholamine responses were completely blocked by the H1-antagonist mepyramine and were insensitive to the H2-antagonist cimetidine. Examination of the time course of accumulation of the individual inositol phosphates stimulated by histamine revealed an early and sustained rise in inositol 1,4-bisphosphate content but not inositol 1,4,5-trisphosphate content at 1 min and the overall largest accumulation of inositol monophosphate after 30 min of stimulation. Pretreatment with the tumor-promoting phorbol ester phorbol 12-myristate 13-acetate (PMA) resulted in a dose-dependent, time-dependent inhibition of histamine-induced inositol phosphate formation and catecholamine secretion. In this inhibitory action, PMA exhibited high potency (IC50 of approximately 0.5 nM), an effect not shared by the inactive phorbol ester 4-alpha-phorbol 12,13-didecanoate. Pretreatment with forskolin, on the other hand, only marginally inhibited the histamine-induced inositol phospholipid metabolism and catecholamine secretion. These data suggest that protein kinase C activation in chromaffin cells may mediate a negative feedback control on inositol phospholipid metabolism.

Actions of somatostatin on perfused bovine adrenal glands and cultured bovine adrenal medullary cells

The effects of somatostatin on catecholamine secretion and inositol phosphate accumulation have been studied using isolated perfused bovine adrenal glands and cultured bovine adrenal medullary cells. Somatostatin had no effect on basal adrenaline or noradrenaline secretion from either preparation. At concentrations above 1 microM, somatostatin inhibited the secretion of both catecholamines induced by 5 microM nicotine from cultured chromaffin cells. In contrast, over the concentration range 0.1 nM-10 microM, somatostatin had no effect on the secretory responses produced by 10 nM angiotensin II or 1 microM histamine. Inositol phosphate accumulation in cultured bovine adrenal medullary cells was unaffected by 0.1 nM-0.1 microM somatostatin, however at 1 and 10 microM somatostatin it was significantly increased, by 23% and 103% respectively. The effects of somatostatin (0.1 nM-10 microM) and of 50 microM muscarine on inositol phosphate accumulation were simply additive. Similarly, somatostatin at 0.1 nM and 10 nM together with 10 nM angiotensin II or 1 microM histamine produced additive inositol phosphate responses. In contrast, 1 microM somatostatin gave significantly more-than-additive (synergistic) inositol phosphate responses with angiotensin II and histamine. The results suggest that some adrenal medullary cells possess several types of receptors, and that these receptors may interact to produce non-additive responses.

Effects of angiotensin II on cultured, bovine adrenal medullary cells

Primary cultures of bovine adrenal medullary cells have been used to study the effects of angiotensin II on catecholamine secretion and inositol phosphate accumulation. Angiotensin II induced a weak secretion of both adrenaline and noradrenaline, with a threshold of 10-100 pM and a shallow concentration-dependence up to 10 microM. The response was fully dependent on extracellular Ca++, was partially inhibited by 100 nM nifedipine, was completely blocked by [Sar1, Ala8]-angiotensin II (IC50 5-10 nM) and was unaffected by 0.1 mM hexamethonium. Angiotensin II also increased inositol phosphate accumulation over the range 1 pM-10 microM. Inositol trisphosphate levels increased in a biphasic manner after 15 sec and 1 min exposure to 10 nM angiotensin II, but were not significantly increased at 30 sec or 5, 15 or 30 min stimulation. Inositol bisphosphate was significantly increased after 1 min. Inositol monophosphate levels only increased after 1 min stimulation, but continued to rise during 30 min stimulation. Removal of extracellular Ca++ or addition of EGTA reduced basal inositol phosphate accumulation but not the ability of angiotensin II to stimulate inositol phosphate accumulation relative to basal. Nifedipine (100 nM) had no effect on basal or angiotensin II-induced inositol phosphate accumulation. The inositol phosphate response to angiotensin II was abolished by 1 microM [Sar1, Ala8]-angiotensin II. The results suggest that secretion of adrenal medullary catecholamines can be evoked by angiotensin II, at concentrations that are compatible with a role for circulating angiotensin II or for angiotensin II generated locally within the adrenal medulla. They do not support the suggestion that the secretory actions of angiotensin II on chromaffin cells are mediated by mobilization of intracellular Ca++ stores.

Lack of effect of opioid compounds on angiotensin II responses of bovine adrenal medullary cells

Angiotensin II (10 nM) increased basal adrenaline and noradrenaline secretion from cultured bovine adrenal chromaffin cells by 2.5- to 3-fold and 4- to 6-fold, respectively, and stimulated basal accumulation of inositol phosphates more than 2-fold. Etorphine and diprenorphine in the range 10(-9) to 10(-5) M had no effect on the catecholamine secretion induced by angiotensin II, and, at 10(-8) and 10(-5) M, had no effect on angiotensin II-induced inositol phosphate accumulation. The functions of adrenal medullary opioid receptors remain to be determined.