Immunocytochemical study of microtubules in chromaffin cells in culture and evidence that tubulin is not an integral protein of the chromaffin granule membrane

Bovine Chromaffin Cells: Culture and Fluorescence Assay for Secretion

Over the last four decades, chromaffin cells originating from the adrenal medulla have been probably one of the most popular cell models to study neurosecretion at the molecular level. Accordingly, numerous seminal discoveries in the field, including the characterization of role of the cytoskeleton, fusogenic lipids, and soluble N-ethylmaleimide-sensitivefactor attachment protein receptor (SNARE) proteins, have been made using this model. In this chapter, we describe a standard method currently used to isolate and culture bovine chromaffin cells, and we illustrate a catecholamine secretion assay based on the successive transformation of adrenaline into adrenochrome and adrenolutine for fluorescence measurements. We also provide some guidelines for efficient cell recovery and for the use of this assay in the laboratory.

Viability and Functionality of Bovine Chromaffin Cells Encapsulated into Alginate-PLL Microcapsules with a Liquefied Inner Core

Implantation of adrenal medullary bovine chromaffin cells (BCC), which synthesize and secrete a combination of pain-reducing neuroactive compounds including catecholamines and opioid peptides, has been proposed for the treatment of intractable cancer pain. Macro- or microencapsulation of such cells within semi-permeable membranes is expected to protect the transplant from the host's immune system. In the present study, we report the viability and functionality of BCC encapsulated into microcapsules of alginate-poly-L-lysine (PLL) with a liquefied inner core. The experiment was carried out during 44 days. Empty microcapsules were characterized in terms of morphology, permeability, and mechanical resistance. At the same time, the viability and functionality of both encapsulated and nonencapsulated BCC were evaluated in vitro. We obtained viable BCC with excellent functionality: immunocytochemical analysis revealed robust survival of chromaffin cells 30 days after isolation and microencapsulation. HPLC assay showed that encapsulated BCC released catecholamines basally during the time course study. Taken together, these results demonstrate that viable BCC can be successfully encapsulated into alginate-PLL microcapsules with a liquefied inner core.

Preparation and culture of adrenal chromaffin cells

Cultured chromaffin cells have been used for almost 40 years in the study of different cell functions using biochemical, electrophysiological, pharmacological, and toxicological approaches. Chromaffin cells are essentially secretory cells that are used to model sympathetic neurons or neuroendocrine cells. In this chapter, we describe the most common methods currently used to isolate and culture chromaffin cells from the animals used most commonly: cows, rats, and mice. We also provide some advice on the use of these cells in the laboratory.

Fluorescent β-Blockers as Tools to Study Presynaptic Mechanisms of Neurosecretion

Several, if not all adrenergic β-blockers (β-Bs), accumulate progressively inside secretory vesicles in a time- and concentration-dependent manner, and could be considered to be false neurotransmitters. This transmitter effect is most likely unrelated to their ability to block adrenergic receptors, but it could explain the delay in lowering arterial pressure in hypertensive patients. We have developed a new drug to monitor the accumulation of β-Bs inside living cells, RCTM-3, which fluoresces in the visible spectrum. Here we describe the procedure to synthesize this new compound, as well as its fluorescent properties, pharmacological profile and its accumulation inside the secretory vesicles of PC12 cells.

S100A10-mediated translocation of annexin-A2 to SNARE proteins in adrenergic chromaffin cells undergoing exocytosis

In neuroendocrine cells, annexin-A2 is implicated as a promoter of monosialotetrahexosylganglioside (GM1)-containing lipid microdomains that are required for calcium-regulated exocytosis. As soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) require a specific lipid environment to mediate granule docking and fusion, we investigated whether annexin-A2-induced lipid microdomains might be linked to the SNAREs present at the plasma membrane. Stimulation of adrenergic chromaffin cells induces the translocation of cytosolic annexin-A2 to the plasma membrane, where it colocalizes with SNAP-25 and S100A10. Cross-linking experiments performed in stimulated chromaffin cells indicate that annexin-A2 directly interacts with S100A10 to form a tetramer at the plasma membrane. Here, we demonstrate that S100A10 can interact with vesicle-associated membrane protein 2 (VAMP2) and show that VAMP2 is present at the plasma membrane in resting adrenergic chromaffin cells. Tetanus toxin that cleaves VAMP2 solubilizes S100A10 from the plasma membrane and inhibits the translocation of annexin-A2 to the plasma membrane. Immunogold labelling of plasma membrane sheets combined with spatial point pattern analysis confirmed that S100A10 is present in VAMP2 microdomains at the plasma membrane and that annexin-A2 is observed close to S100A10 and to syntaxin in stimulated chromaffin cells. In addition, these results showed that the formation of phosphatidylinositol (4,5)-bisphosphate (PIP(2)) microdomains colocalized with S100A10 in the vicinity of docked granules, suggesting a functional interplay between annexin-A2-mediated lipid microdomains and SNAREs during exocytosis.

Intrathecal grafting of porcine chromaffin cells reduces formalin-evoked c-Fos expression in the rat spinal cord

Chromaffin cells from the adrenal gland secrete a combination of neuroactive compounds including catecholamines, opioid peptides, and growth factors that have strong analgesic effects, especially when administered intrathecally. Preclinical studies of intrathecal implantation with xenogeneic bovine chromaffin cells in rats have provided conflicting data with regard to analgesic effects, and recent concern over risk of prion transmission has precluded their use in human clinical trials. We previously developed a new, safer source of adult adrenal chromaffin cells of porcine origin and demonstrated an in vivo antinociceptive effect in the formalin test, a rodent model of tonic pain. The goal of the present study was to confirm porcine chromaffin cell analgesic effects at the molecular level by evaluating neural activity as reflected by spinal cord c-Fos protein expression. To this end, the expression of c-Fos in response to intraplantar formalin injection was evaluated in animals following intrathecal grafting of 10(6) porcine or bovine chromaffin cells. For the two species, adrenal chromaffin cells significantly reduced the tonic phases of the formalin response. Similarly, c-Fos-like immunoreactive neurons were markedly reduced in the dorsal horns of animals that had received injections of xenogeneic chromaffin cells. This reduction was observed in both the superficial (I-II) and deep (V-VI) lamina of the dorsal horn. The present study demonstrates that both xenogeneic porcine and bovine chromaffin cells transplanted into the spinal subarachnoid space of the rat can suppress formalin-evoked c-Fos expression equally, in parallel with suppression of nociceptive behaviors in the tonic phase of the test. These findings confirm previous reports that adrenal chromaffin cells may produce antinociception by inhibiting activation of nociceptive neurons in the spinal dorsal horn. Taken together these results support the concept that porcine chromaffin cells may offer an alternative xenogeneic cell source for transplants delivering pain-reducing neuroactive substances.

Nitric oxide donors induce calcium-mobilisation from internal stores but do not stimulate catecholamine secretion by bovine chromaffin cells in resting conditions

The potential role of nitric oxide (NO) donors and peroxynitrites on both basal catecholamine (CA) secretion and modulation of calcium levels has been investigated in primary cultures of bovine chromaffin cells. NO donors did not modulate catecholamine secretion, while peroxynitrites induced a time dose-dependent increase in basal CA secretion. Two facts may explain the lack of these compounds on basal CA secretion. NO donors induce, on the one hand, an increase in intracellular calcium levels by depletion of internal IP3-stores from endoplasmic reticulum. On the other hand, a small calcium influx through N-type voltage-dependent calcium channels (VDCC), which seem not to be coupled to exocytosis of adrenaline and noradrenaline in chromaffin cells. Both effects, calcium-mobilisation from internal stores and calcium entry through N-type VDCC are mediated by cGMP synthesis. In contrast, peroxynitrites induce an increase in basal CA secretion by both a decrease of intracellular catecholamine content and a toxic effect on cellular membrane. All these results, taken together, could explain contradictory results in the literature on the role of NO on basal catecholamine secretion and on modulation of intracellular calcium in chromaffin cells.

Intrathecal xenogeneic chromaffin cell grafts reduce nociceptive behavior in a rodent tonic pain model

Adrenal medullary chromaffin cells synthetize and secrete a combination of pain-reducing neuroactive compounds including catecholamines and opioid peptides. Previous reports have shown that implantation of chromaffin cells into the spinal subarachnoid space can reduce both acute and chronic pain in several animal models. We recently demonstrated that human chromaffin cell grafts in the cerebrospinal fluid (CSF) could alleviate intractable cancer pain after failure of systemic opiates. However, wider application of this approach was limited by the limited availability of allogeneic donor material. Alternatively, chromaffin cells from xenogeneic sources such as bovine adrenal medulla were successful in the experimental treatment of pain, but recent concern over risk of prion transmission precluded use of bovine grafts in human clinical trials. The objective of the present study was to investigate the possibility of developing a new xenogeneic porcine source of therapeutic chromaffin cells because this strategy is currently considered the safest for transplantation in man. In the present study, we report the isolation and the characterization of primary porcine chromaffin cells (PCC) compared to bovine cells. We show, for the first time, that these cells grafted in the rat subarachnoid space can attenuate pain-related behaviors as assessed by the formalin test, a model of tonic pain. Moreover, in addition to behavioral studies, immunohistochemical analysis revealed robust survival of chromaffin cells 35 days after transplantation. Taken together, these results support the concept that porcine chromaffin cells may offer an alternative xenogeneic cell source for transplants delivering pain-reducing neuroactive substances.

Molecular mechanisms of glutamate release by bovine chromaffin cells in primary culture

Previous work indicated that glutamate could be involved in the regulation of catecholamine secretion in bovine chromaffin cells. Thus, the question arises on the source of this putative regulatory glutamate. In this work we have examined the possibility that glutamate could be released from chromaffin cells. Data from this study indicate that chromaffin cells are able to release glutamate when they are stimulated by different depolarising agents such as 60 mM KCl, 1 mM 4-aminopyridine or 50 microM veratridine. The amount of glutamate released by these compounds was 0.32 nmol/10(6) cells (9.24% of cellular glutamate content), 0.275 (7.86%) and 0.158 (4.52%) for KCl, 4-AP and veratridine stimulation, respectively. All these catecholamine-secretagogues induced glutamate secretion by two mechanisms: 1) a Ca(2+)-dependent, probably exocytotic, mechanism and 2) a Ca(2+)-independent mechanism mediated by reversion of the electrogenic glutamate transporter. Analysis of Ca(2+)-dependent and independent releases for different compounds carried out by several experimental approaches, indicate that Ca(2+)-dependent release was the predominant mechanism for release induced by 4-aminopyridine (84% of total release) and high KCl (63%) whilst Ca(2+)-independent release was predominant for veratridine (67%). The Ca(2+)-dependent glutamate release evoked by depolarisation of chromaffin cells with high KCl and 4-AP could be split into both a fast and a slow kinetic component, which might correspond to the release of docked and mobilised chromaffin granules, respectively. On the other hand, depolarisation of cells with veratridine result in glutamate release with only the fast kinetic component. In the case of 60 mM KCl-evoked glutamate release, the fast component exhibited a decay time of <1 s and accounted for 0.63 nmol glu/6x10(6) cells (70% of total exocytotic release), whereas the slow component, which exhibited a decay time of 231 s, accounted for the release of 0.27 nmol glu/6x10(6) cells (30% of total exocytotic release). By contrast in the case of 4-aminopyridine the fast component of exocytosis only represents a 19% of total secretion and the slow a 81% with a decay time of 94 s. These data are very similar to those found in neurones and support the possible intracellular origin of glutamate having a role in the regulation of catecholamine secretion from chromaffin cells. In support of this, we have found that glutamate secretion could be evoked by stimulation of the nicotinic cholinergic receptors.

Neuronal nitric oxide synthase modulates basal catecholamine secretion in bovine chromaffin cells

The role of endogenously produced nitric oxide (NO) in the regulation of basal catecholamine (CA) secretion was studied in chromaffin cells. Treatment of chromaffin cells with nitric oxide synthase (NOS) inhibitors produced a dose-dependent increase in basal catecholamine secretion, which paralleled their ability to inhibit NOS activity. This inhibitory profile was similar to that found in neurons, suggesting the constitutive expression of neuronal NOS (nNOS) in these cells, which was confirmed by Western blot analysis. A study of the kinetics and pharmacology of nNOS activity expressed in chromaffin cells in culture indicated that NOS activity is calcium-dependent, increases with time, and is highly dependent on both intracellular concentrations of L-arginine (K(m) approximately 4 microM, V(max) = 908 +/- 60 pmol/hr x 10(6) cells) and transport of L-arginine into the cells (exhibiting two affinity constants of k(1) = 3.2 +/- 0.3 microM and k(2) = 126 +/- 5.5 microM). The effects of NOS inhibitors on CA secretion were mediated by the L-arginine-NO-cGMP pathway, insofar as exogenous L-arginine was able to partially block the increase in CA secretion evoked by them, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ), a specific inhibitor of guanylate cyclase, and zaprinast, an inhibitor of the cGMP phosphodiesterase, were able to increase and inhibit, respectively, basal CA secretion in a dose-dependent manner. These results suggest that chromaffin cells exhibit a tonic production of NO by nNOS that keeps the basal CA secretion at low levels, and this could be necessary for maintaining a normotensive state.

Annexin II in exocytosis: catecholamine secretion requires the translocation of p36 to the subplasmalemmal region in chromaffin cells

Annexin II is a Ca(2+)-dependent membrane-binding protein present in a wide variety of cells and tissues. Within cells, annexin II is found either as a 36-kD monomer (p36) or as a heterotetrameric complex (p90) coupled with the S-100-related protein, p11. Annexin II has been suggested to be involved in exocytosis as it can restore the secretory responsiveness of permeabilized chromaffin cells. By quantitative confocal immunofluorescence, immunoreplica analysis and immunoprecipitation, we show here the translocation of p36 from the cytosol to a subplasmalemmal Triton X-100 insoluble fraction in chromaffin cells following nicotinic stimulation. A synthetic peptide corresponding to the NH2-terminal domain of p36 which contains the phosphorylation sites was microinjected into individual chromaffin cells and catecholamine secretion was monitored by amperometry. This peptide blocked completely the nicotine-induced recruitment of p36 to the cell periphery and strongly inhibited exocytosis evoked by either nicotine or high K+. The light chain of annexin II, p11, was selectively expressed by adrenergic chromaffin cells, and was only present in the subplasmalemmal Triton X-100 insoluble protein fraction of both resting and stimulated cells. p11 can modify the Ca(2+)- and/or the phospholipid-binding properties of p36. We found that loss Ca2+ was required to stimulate the translocation of p36 and to trigger exocytosis in adrenergic chromaffin cells. Our findings suggest that the translocation of p36 to the subplasmalemmal region is an essential event in regulated exocytosis and support the idea that the presence of p11 in adrenergic cells may confer a higher Ca2+ affinity to the exocytotic pathway in these cells.

Pharmacological modulation of adrenal medullary GABAA receptor: consistent with its subunit composition

1. Muscimol, the specific GABAA receptor agonist, increased the secretion of catecholamines by chromaffin cells with an EC50 of 2.9 +/- 0.4 microM. 2. GABAA receptors of these cells were modulated by the same drugs which modulate GABAA receptors in brain tissue. 3. Benzodiazepines enhanced muscimol-evoked catecholamine secretion by between 20 and 80%. This effect seems to be mediated by binding to a central type of benzodiazepine receptor because it was completely blocked by the specific antagonist, Ro 15 1788. This antagonist was able to displace [3H]-flunitrazepam binding with an EC50 of 0.26 +/- 0.05 nM. 4. beta-Carbolines weakly inhibited muscimol-induced catecholamine secretion and were able to displace [3H]-flunitrazepam binding with an EC50 between 0.2 and 0.9 nM, depending on the beta-carboline used. 5. Pregnanolone and related neuroactive steroids enhanced muscimol-evoked catecholamine secretion by up to 87%, in a dose-dependent fashion. In contrast pregnenolone weakly inhibited muscimol-evoked catecholamine secretion. 6. Zn2+ did not affect GABAA receptor-induced catecholamine secretion. 7. These pharmacological results are absolutely concordant with the theoretical properties given by the GABAA receptor subunit composition of bovine adrenal medulla -alpha 1, alpha 4, beta 1-3, gamma 2-previously characterized by Western blot analysis.

ADP exerts a protective effect against rundown of the Ca2+ current in bovine chromaffin cells

In isolated chromaffin cells, the high-voltage-activated Ca2+ current, recorded using 5 mM Ca2+ as the divalent charge carrier, exhibits rundown within 10 min, which is delayed for 1 h at least by the addition of 1 mM adenosine 5'-triphosphate (ATP) to the pipette medium. The mechanism of this stabilizing action of ATP has been examined. ATP action is dose dependent; the rundown process, which was delayed at concentrations below 0.4 mM, was totally abolished at higher concentrations. The requirement for ATP was shown to be quite strict: 2 mM inosine 5'-triphosphate (ITP) could not replace ATP, whereas guanosine 5'-triphosphate (GTP) could, but at higher concentrations. This effect of ATP was shown to require the presence of MgCl2 and the liberation of a phosphate group since the ATP analogue 5'-adenylyl-imidodiphosphate (AMP-PNP) could not act as a substitute for ATP, suggesting an action through either adenosine 5'-diphosphate (ADP) or a phosphorylation step. ADP, in the presence of Mg2+ only, could replace ATP in the same concentration range. This effect was shown to be specific to ADP; it was maintained after blocking the pathways which convert ADP into ATP, and could not be mimicked by guanosine 5'-diphosphate (GDP). Similarly, ATP and ADP effects were abolished at an increased internal Ca2+ concentration (pCa 6 instead of pCa 7.7, where pCa = -log10[Ca2+]). Nevertheless, the presence of 1 mM Mg-ADP in the bathing solution did not prevent the rundown of the Ca2+ channels when going to the inside-out patch recording configuration.(ABSTRACT TRUNCATED AT 250 WORDS)

GABAB receptors increase intracellular calcium concentrations in chromaffin cells through two different pathways: their role in catecholamine secretion

The activation of GABAB receptors of adrenal chomaffin cells produces an increase of [Ca2+]i measured by fura-2 AM techniques. GABAB agonists 3-aminopropylphosphinic acid or (-)baclofen, at concentrations of 0.5 mM, increased basal Ca2+ values 332 +/- 60.9 and 306 +/- 40.5 nM, respectively, in cells suspended in a 2.5 mM Ca2+ buffer. The GABAB-induced increase of [Ca2+]i seemed to have two different components. The first was due to an entry from the extracellular medium mainly through L-type voltage-dependent Ca2+ channels as the dihydropiridine nifedipine 50 microM was able to decrease it more than 60%, while omega-conotoxin, which blocks N-type channels, did not produce any change in the GABAB-evoked Ca2+ increment. The second component was due to a release of Ca2+ from intracellular pools and was about one-third of the total GABAB-induced increase of [Ca2+]i. GABAB receptors stimulated inositol 1,4,5-trisphosphate-sensitive and not the caffeine-sensitive Ca2+ store. In a low-Ca2+ buffer after treatment with 2 microM angiotensin II, neither 0.5 mM 3-APPA nor baclofen were able to produce an additional increase of [Ca2+]i, whereas 4 mM caffeine had no effect on GABAB response. This intracellular Ca2+ mobilization could be due to inositol 1,4,5-trisphosphate accumulation produced by the activation of GABAB receptors. In fact, the specific agonists after 10 minutes incubation produced a dose-dependent increase of inositol 1,4,5-trisphosphate. The maximal effect was obtained at 100 microM baclofen and 3-APPA, and it was 3.63 +/- 0.75 and 3.2 +/- 1.5 times the basal levels (7.3 +/- 0.3 pmol/10(6) cells), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition by cyclothiazide of neuronal nicotinic responses in bovine chromaffin cells

1. The desensitizing acetylcholine (ACh) response of bovine chromaffin cells maintained in culture was examined using rapid agonist applications (of 2 s duration) which imposed nominal drug concentrations within 50 ms. This study was aimed, firstly, at identifying which of the alpha 3, alpha 4 and alpha 7 subunits known to be present in these cells is predominant in the ACh-evoked response and secondly, on the effects on these neuronal nicotinic ACh receptors (AChR) of cyclothiazide (CT), an agent acting as a modulator of a gating desensitization site on other ligand-gated channels. 2. Locally applied 100 microM ACh evoked peak currents (IACh) of -1.5 +/- 0.1 nA (n = 83) at a holding potential of -60 mV. The ACh dose-response curve yielded an estimated EC50 of 60 microM. This current was not sustained but desensitized during the application period; it displayed strong inward rectification, but desensitized equally whether the evoked current was inward or outward going. The latter observation excludes alpha 4 as a major contributor to the recorded current. Because the response was almost insensitive to a 1 microM alpha-bungarotoxin pretreatment (IACh = -1.2 +/- 0.1 nA; n = 6), and because 1, 1-dimethyl-4-phenylpiperazinium (DMPP) works as a potent agonist (peak current = -1.9 nA, n = 2 for 100 microM DMPP), the alpha 7 subunit is also a minor contributor to the response. Taken together, these observations suggest a dominant alpha 3 type of response. 3. Triple exponential fits were used to describe the characteristics of the ACh-evoked currents; one component to fit the rising phase, with 2 components to describe the decay phase. The decay times were 100 ms and 4 s for the fast and slow components respectively. The rate of the slow decay component increased systematically with recording time, approximately doubling from its initial value within 20-40 min. Furthermore there was a gradual rundown of the response, seen first as a loss of the late component of the current, measured at 2 s, with the peak current amplitude decreasing later in the recording.4. CT, when coapplied with ACh, produced a dose-dependent inhibition of the ACh-evoked peak current. The effect showed little voltage-dependency with 100 microM CT producing 46 +/- 5% (s.d.; n = 3)and 47 +/- 8% (s.d.; n = 7) inhibition at -100 and -60 mV respectively. At + 60 mV, inhibition was estimated to be 26 +/- 7% (s.d.; n = 3).5. After pre-exposure of the cells to CT by bath application, 10 and 30 microM CT produced poorly reversible 20 +/- 9% (n = 7) and 42 +/- 5% (n = 4) inhibitions of the peak current respectively. There were no discernible effects on the fitted decay constants at any CT concentration tested, although an increased inhibitory effect of CT was observed at higher concentrations (100 microM) on the amplitude of the late component measured at 2 s.6. Similar effects were observed in conditions chosen to isolate the alpha 3 type of receptor: namely when using DMPP as an agonist, or after a-bungarotoxin pretreatment.7. The 2,3-benzodiazepine, GYKI 53655, is known to antagonize the action of CT on AMPA receptors.Coapplication of 50 microM GYKI 53655 with ACh (100 microM) produced a 29 +/- 4% inhibition of the peak ACh-evoked current and 44 +/- 6% inhibition of its amplitude at 2 s (n = 4). This response was fully reversible. Brief applications of both CT (100 microM) and GYKI 53655 (50 microM) with ACh via the microperfusion system produced a fully reversible inhibition that was not significantly different from the values obtained with either CT or GYKI 53655 alone, with 37 +/- 6% inhibition of peak and 61 +/- 9%inhibition of the amplitude at 2 s (n = 3).8. The results obtained suggest that the CT effect is to impede recovery from a slow desensitization,with a more pronounced effect with longer CT applications. Globally, CT favours the 'rundown state' of the neuronal nicotinic AChR.

A reassessment of the modulatory role of cyclic AMP in catecholamine secretion by chromaffin cells

1. The role of adenosine 3':5'-cyclic monophosphate (cyclic AMP) in the regulation of catecholamine (CA) secretion in chromaffin cells remains equivocal from previous studies. 2. In the present study the effect of this cyclic nucleotide on basal CA secretion, as well as on intracellular calcium and membrane potential has been examined. 3. Forskolin and the permeable cyclic AMP analogue, 8-(4-chlorphenylthio)-adenosine-3'-5' monophosphate cyclic (pClpcAMP), increased basal CA secretion in a dose-dependent manner. The EC50s were 0.43 +/- 0.10 microM for forskolin and 39 +/- 9 microM for pClpcAMP. Other agonists with adenylate cyclase activity such as stimulants of adenosine receptors, beta-adrenoceptors, GABAB receptors and intestinal vasoactive peptide (VIP), also increased basal CA secretion in a highly significant manner. However, when they were added together with forskolin, CA secretion was not affected although an additive increase in cyclic AMP levels was produced. 4. Statistical analysis of the correlation between cyclic AMP levels and CA secretion evoked by these cyclic AMP increasing compounds showed that a significant direct correlation between both parameters existed only when low levels of cyclic AMP were produced by secretagogue stimulation. When the increase in intracellular cyclic AMP concentrations exceeded approximately 8 times the basal cyclic AMP levels the correlation was not significant. These results indicate a dual dose-dependent effect of cyclic AMP on basal CA secretion. 5. The stimulatory effect of low cyclic AMP on basal CA secretion was accompanied by an increase in membrane potential and in intracellular calcium concentrations ([Ca2+]j), the latter mainly being due to an increase in intracellular Ca2+ entry through L-type voltage-dependent Ca2" channels.6. The possible mechanisms involved in these cyclic AMP effects are discussed.

Evolution of the Ca2+ current during dialysis of isolated bovine chromaffin cells: effect of internal calcium

We have examined the internal Ca(2+)-dependence of the long-term evolution of whole cell high voltage activated Ca current in chromaffin cells. The evolution of the peak Ca current was characterized by 2 distinct phases: after an initial facilitation, there followed a rundown, which represented a reduction by 70% within some 10 min. The rundown process was shown not to depend on Ca2+ entry nor on membrane depolarization. It resulted from cell dialysis with a saline solution and, once initiated, it proceeded at a rate of 0.28 min-1 at 4 different Ca2+ concentrations (pCa 5-9). The facilitation is also initiated by cell dialysis but this process developed faster at higher internal Ca2+ concentrations. Thus, globally, high-voltage activated Ca2+ current runs down faster when using a recording pipette solution with a higher internal Ca2+ concentration (pCa 5 or 6). Some leupeptin-sensitive proteases may be involved in the initiation of facilitation and rundown processes.

GABAB receptors modulate catecholamine secretion in chromaffin cells by a mechanism involving cyclic AMP formation

1. The function of gamma-aminobutyric acidB (GABAB) receptors in modulation of catecholamine secretion by chromaffin cells and the possible mechanism involved in this action have been examined. 2. The GABAB agonists (-)-baclofen and 3-aminopropylphosphinic acid (3-APPA) were found to induce a dose-dependent increase of basal catecholamine secretion. The EC50s were 151 +/- 35 microM and 225 +/- 58 microM for baclofen and 3-APPA, respectively. This stimulatory effect was specific since it could be blocked by 0.5 mM of the specific GABAB antagonist CGP-35348. 3. In contrast, preincubation of chromaffin cells with the GABAB agonists was found to inhibit, in a dose-dependent manner, the catecholamine secretion evoked by 10 microM nicotine and 200 microM muscimol. 4. The effects of GABAB agonists on both basal and evoked catecholamine secretion were found to be accompanied by parallel changes in intracellular calcium concentration ([Ca2+]i). GABAB agonists produced a dose-dependent increase in [Ca2+]i which was partially blocked by CGP 35348, but they produced a strong inhibition of the [Ca2+]i increase induced by nicotine and muscimol. 5. The GABAB agonists also produced a dose-dependent increase in intracellular cyclic AMP levels, there being a direct correlation between both increase in catecholamine secretion and in intracellular cyclic AMP levels. 6. The pretreatment of chromaffin cells with pertussis toxin doubled the catecholamine secretion and increased by four times the intracellular cyclic AMP levels evoked by GABAB agonists. 7. The possible involvement of adenylate cyclase in the mechanism of GABAA receptor modulation of catecholamine secretion is discussed.

Voltage-dependent calcium entry in confluent bovine capillary endothelial cells

Confluent bovine capillary endothelial cells display, when examined for voltage-dependent calcium entries using cell-attached channel recordings, two types of Ca2+ channels (4 and 23.5 pS in 110 mM Ba2+) both sensitive to the dihydropyridine Ca agonist BAY K 8644. In contrast to isolated cells, confluent cells display no T-type, low threshold activity, and Ca currents were typically only elicited at very depolarized potentials. In these cells, voltage-dependent calcium entries will only be made operative by substances able to shift their activation towards the resting potential.

Primary structure of an agonist binding subunit of the nicotinic acetylcholine receptor from bovine adrenal chromaffin cells

Activation by acetylcholine of a nicotinic acetylcholine receptor on the membrane of bovine chromaffin cells leads to membrane depolarization and to the subsequent triggering of catecholamine secretion. It is evident that acetylcholine receptors play a central role in the initial phase of the secretion process and, therefore, an extensive characterization of their molecular components and properties is of fundamental interest. With this intention, we have screened bovine adrenal medullary cDNA libraries with a probe coding for a fragment of the rat muscle acetylcholine receptor alpha subunit. Several cDNA clones were isolated. The longest cDNA had an open reading frame encoding a 495-amino acid protein with a molecular weight of 56,911. The deduced primary structure contains features that indicate that the encoded protein is an alpha or acetylcholine binding subunit, and, in fact, it manifests significant sequence similarity to previously cloned alpha subunits. Sequence identity is particularly high with the alpha 3 subunit, which is expressed in the rat pheochromocytoma PC12 cell line and in several brain areas, and, consequently, it is considered a component of a neuronal acetylcholine receptor. Accordingly, the present results suggest that the agonist binding subunit of the nicotinic acetylcholine receptor from bovine chromaffin cells is an alpha 3-type subunit, corroborating previous immunological and pharmacological evidence for the presence of a neuronal nicotinic receptor in chromaffin cells.

Mechanism through which GABAA receptor modulates catecholamine secretion from bovine chromaffin cells

The actions and mechanism of GABAergic modulation of catecholamine secretion from isolated bovine chromaffin cells were investigated. The GABAA receptor agonist muscimol induced a fast rise in cytosolic [Ca2+]. The mean peak increase was 290 +/- 30 nM over basal levels. The increase in cytosolic [Ca2+] was abolished in the absence of extracellular [Ca2+] and was blocked by the GABAA antagonist bicuculline and the dihydropiridine nifedipine. Muscimol also elicited the release of catecholamines and increased the bisoxonol fluorescence indicating a cell depolarization. The [Ca2+] entry was well correlated with muscimol-evoked catecholamine secretion. When cells were treated with muscimol and a second secretagogue, a biphasic behavior was revealed. Muscimol enhanced the catecholamine release evoked by low concentrations of nicotine or K+, whereas release obtained at high concentrations of nicotine or K+ was actually inhibited. When the muscimol effect on membrane potential was studied in the presence of low K+ or nicotine concentrations, an enhancement of the bisoxonol fluorescence was observed. This effect was reversed at high concentrations of both K+ and nicotine. Measurement of 36Cl- fluxes showed an increase in membrane permeability to Cl- during muscimol stimulation. The influx or efflux in Cl- was dependent on membrane potential. In normal conditions, with a K+ concentration of 5.4 mM, a Cl- efflux was observed by both radiometric techniques, with 36Cl- and by the use of the chloride-sensitive fluorescent probe 6-methoxy-N-(3-sulphopropil)quinolinium, as indicator of intracellular Cl-. At high nicotine (20 mM) or K+ concentrations (105 mM) a Cl- influx was observed using 6-methoxy-N-(3-sulphopropil)quinolinium.(ABSTRACT TRUNCATED AT 250 WORDS)

Voltage-gated Ca entry in isolated bovine capillary endothelial cells: evidence of a new type of BAY K 8644-sensitive channel

Isolated bovine capillary endothelial cells have been examined for voltage-dependent Ca entry. All cells displayed a low threshold activity, with the main characteristics of a T-type transient current, when examined using whole-cell recording for activation and inactivation and cell-attached conditions or inside-out patches for the elementary conductance (8 pS). 25% of the cells displayed an additional sustained current in 5 mM CaCl2 above -40 mV, which was enhanced by application of BAY K 8644, but almost insensitive to superfusion with nicardipine. Two types of channels (2.8 and 21 pS, in 110 mM BaCl2) were shown to have a BAY K 8644 sensitivity. The large conductance channels were L-type channels. The smaller events were elicited at more hyperpolarized potentials (by some 30 mV). Their mean open time was 16 ms in control conditions. In presence of BAY K 8644, additional long open times were observed (up to 100 ms as compared to 7.8 ms for the time constants of the slow mode of the L-type channel). We refer to these channels as SB channels: of small conductance and sensitive to BAY K 8644. In the presence of nicardipine, SB channels are not noticeably modified, in contrast to the L-type openings which are abolished. Also, SB open times are close to control values when nicardipine is added after a BAY K 8644 application. We suggest that, at physiological concentrations of divalent ions, an SB-type activity is elicited above -40 mV which generates the low threshold sustained current.

Inactivation characteristics reveal two calcium currents in adult bovine chromaffin cells

1. Two calcium currents were identified by differences in their inactivation characteristics in adult chromaffin cells maintained in short-term primary culture (3-5 days). Calcium currents were recorded by means of the whole-cell configuration using an intracellular medium highly buffered for pH and pCa. 2. Calcium current evoked from a holding potential of -90 mV inactivated along two components: an initial transient with a time constant of 250 ms followed by a plateau. 3. Steady-state inactivation followed two processes which developed at two distinct membrane potentials. One process was half-inactivated at low voltages around -55 mV and affected mainly the initial transient component. The other process, which affected mainly the sustained component of the calcium current, was half-inactivated at voltages around -10 mV. The proportions of these two processes varied greatly from cell to cell. 4. The dihydropyridine antagonists (nicardipine and nifedipine applied at 10(-5) M) and the phenylalkylamine D600 (5 x 10(-6) M) shifted the half-inactivation value towards -55 mV, indicating the suppression of the sustained component. The snail toxin, omega-conotoxin, had the opposite effect; it shifted the half-activation value towards -10 mV. 5. The calcium channel agonist Bay K 8644 (10(-5) M) either had no effect or induced only a slight increase of the response, as did its (-)-enantiomer (10(-6) M). To interpret the present results, we suggest that the L-component was maximally activated in our recording conditions. 6. In chromaffin cells, the calcium current recorded in whole-cell conditions is composed of two components with properties close to those of N- and L-type currents described in sympathetic neurons.

Prolactin inhibits the activity of tyrosine hydroxylase in cultured bovine adrenal chromaffin cells in a dose-dependent manner

Prolactin can modulate the adrenal medulla function, but it has not yet been established whether its action is directly exerted on the adrenal medulla cells. In this work, we have studied the effect of several concentrations of prolactin on the synthesis, storage and release of norepinephrine and epinephrine using cultured bovine adrenal chromaffin cells. In these cells, prolactin inhibited the activity of tyrosine hydroxylase, the rate-limiting enzyme in the catecholamine synthesis, in a dose-dependent manner, from a concentration above 50 ng/ml of prolactin in the incubation medium. Surprisingly, this dose-dependent decrease was not accompanied by changes in the catecholamine release, since the secretion of both norepinephrine and epinephrine as well as the total catecholamine secretion were not significantly altered by the different prolactin concentrations. Moreover, the cellular content of both catecholamines was not altered by prolactin. In summary, these observations allow us to conclude that prolactin exerts a direct inhibitory effect on the tyrosine hydroxylase activity in cultured adrenal chromaffin cells without altering catecholamine release.

Mechanisms of [3H] gamma-aminobutyric acid release by chromaffin cells in primary culture

The basal and evoked [3H] gamma-aminobutyric acid (GABA) release from chromaffin cells in primary cultures was studied and compared with that of [3H]NA. [3H]GABA was found to be released, in a dose-dependent fashion, by different secretagogues known to induce noradrenaline (NA) release, that is, the cholinergic agonist nicotine, high-potassium chloride, veratridine, and calcium ionophores. In general, there was a parallelism between percentages of release of both [3H]GABA and [3H]NA, although in all circumstances the former were lower. The nicotine- and high-potassium-evoked [3H]GABA release was absolutely calcium dependent, thus indicating the existence of a exocytotic-like mechanism, whereas in the veratridine-induced release, a calcium-independent component was also detected. This latter component was sodium dependent, as it showed an absolute requirement for extracellular sodium and was enhanced by ouabain. Moreover, it was inhibited by known GABA uptake inhibitors, which indicate that this component of [3H]GABA release induced by veratridine could be due to GABA outflow through the membrane carrier. The above results, together with that obtained from studies about subcellular localization of [3H]GABA taken up by chromaffin cells, seem to support the existence of two mechanisms for [3H]GABA release by chromaffin cells: one calcium-dependent, exocytotic-like, and another calcium-independent and sodium-dependent, possibly mediated by the GABA carrier. Both processes could have a functional role on the regulation of extracellular GABA levels and so in the control of catecholamine release by chromaffin cells.

Voltage-dependent transient calcium currents in freshly dissociated capillary endothelial cells

Dissociated capillary endothelial cells display a voltage-dependent Ca current activating around the resting potential. The initial transient component of the current corresponds to a Ca channel of the T type. Some cells also display a plateau component corresponding to a distinct dihydropyridine-sensitive Ca channel. Depolarization induced by high external K+ elicits an increase in cytoplasmic Ca concentration. Confluent cells have been found to express the same Ca permeabilities.

GABAA and GABAB receptors are functionally active in the regulation of catecholamine secretion by bovine chromaffin cells

GABA stimulates the basal catecholamine release from adrenal bovine chromaffin cells in a calcium-dependent manner. This release represents about 70% of that obtained by similar doses of nicotine under similar experimental conditions. This effect is mediated by GABAA receptor sites present in chromaffin cells, since it was mimicked by muscimol and reversed by bicuculline. In addition, GABA, through its GABAA receptors, increases the catecholamine release evoked by submaximal doses of nicotine, but it has no effect on nicotine-evoked secretion of catecholamines when nicotine was given at maximal doses. These results seem to indicate that both nicotine and GABA release catecholamines from the same intracellular pool. In contrast, baclofen, a GABAB receptor agonist, depressed both basal and nicotine-evoked catecholamine release; this result indicates that in addition to GABAA control of catecholamine secretion by chromaffin cells, there is a GABAB control of this function. These results support the existence of a dual regulation of catecholamine secretion by both the GABAA and GABAB receptors in a similar way as that proposed for muscarinic and nicotinic cholinergic receptors.

Effect of secretagogues on chromogranin A synthesis in bovine cultured chromaffin cells. Possible regulation by protein kinase C

Chromogranin A is a major component of storage granules in many different secretory cell types. After [35S]methionine labelling of proteins from cultured bovine chromaffin cells, chromogranin A was immunoprecipitated with specific antibodies, and the radioactivity incorporated into chromogranin A was determined and used as an index of its synthesis rate. Depolarization of cells with nicotine or high K+ evoked a Ca2+-dependent increase in chromogranin A synthesis, whereas muscarine, which does not evoke significant Ca2+ influx from bovine chromaffin cells, had no effect on chromogranin A synthesis. Forskolin, an activator of adenylate cyclase, affected neither the basal nor the nicotine-stimulated rate of chromogranin A synthesis. In contrast, 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, significantly enhanced the incorporation of radioactivity into chromogranin A. Sphingosine, an inhibitor of protein kinase C, abolished both nicotine-stimulated and TPA-induced chromogranin A synthesis. In addition, long-term treatment of chromaffin cells with TPA decreased protein kinase C activity and inhibited the nicotine-stimulated chromogranin A synthesis. These results suggest that protein kinase C may play an important role in the control of chromogranin A synthesis.

Secretion from chromaffin cells is controlled by chromogranin A-derived peptides

Chromogranin A (CGA) is the major protein of the secretory granule from chromaffin cells and also is found in a variety of endocrine cells. Although the sequence of this acidic glycoprotein has been elucidated recently, its biological function is unknown. Here we have purified CGA from chromaffin granules; the final preparation contained the 74-kDa native CGA together with two degradation products--three bands near 60 kDa and a single band of 43 kDa. This preparation was found to inhibit (a maximum inhibition of 60% at 1 microM) the nicotine-induced, but not the high K+-evoked, catecholamine secretion from bovine chromaffin cells maintained in primary culture. Spontaneous release was also affected in the nanomolar CGA protein concentration range. The observation that the inhibitory effect is strictly dependent on a preincubation step together with the modification of the CGA protein profile during this preincubation step suggests that the degradation peptide(s) rather than the 74-kDa native CGA--the approximately equal to 60-kDa bands or the 43-kDa singlet band--is actually involved in secretory cell activity. This was demonstrated by using trypsin-generated peptides that were inhibitory without the preincubation period. The finding that unprocessed CGA is not active on chromaffin cell secretion suggests that this molecule is a precursor of a peptide(s) that is able to regulate catecholamine secretion. Thus, the present data suggest that a CGA-derived peptide(s) could exert a feedback control on chromaffin cell secretory activity--a mechanism that might be of importance during stress situations.

Alpha-melanocyte stimulating hormone promotes neurite outgrowth in chromaffin cells

Chromaffin cells from adult bovine adrenal medulla were found to develop neurites when cocultured with pituitary intermediate lobe (IL) cells. In coculture 51.7% of the chromaffin cells extended neurites compared with 12% in control cultures (chromaffin cells alone). A soluble factor released by IL cells was apparently involved as medium conditioned by contact with IL cells also promoted neurite outgrowth. Moreover, the addition of alpha MSH, one of the pro-opiomelanocortin-derived peptides secreted by IL cells, alone reproduced this effect in a dose-dependent manner. The data provide evidence for a neurotrophic role of alpha MSH.

The synaptic vesicle and the cytoskeleton

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Further characterization of dopamine release by permeabilized PC12 cells

Rat pheochromocytoma cells (PC12) permeabilized with staphylococcal alpha-toxin release [3H]dopamine after addition of micromolar Ca2+. This does not require additional Mg2+-ATP (in contrast to bovine adrenal medullary chromaffin cells). We also observed Ca2+-dependent [3H]-dopamine release from digitonin-permeabilized PC12 cells. Permeabilization with alpha-toxin or digitonin and stimulation of the cells were done consecutively to wash out endogenous Mg2+-ATP. During permeabilization, ATP was removed effectively from the cytoplasm by both agents but the cells released [3H]dopamine in response to micromolar Ca2+ alone. Replacement by chloride of glutamate, which could sustain mitochondrial ATP production in permeabilized cells, does not significantly alter catecholamine release induced by Ca2+. However, Mg2+ without ATP augments the Ca2+-induced release. The release was unaltered by thiol-, hydroxyl-, or calmodulin-interfering substances. Thus Mg2+-ATP, calmodulin, or proteins containing -SH or -OH groups are not necessary for exocytosis in permeabilized PC12 cells.

Chromogranin A synthesis and secretion in chromaffin cells

A sensitive and selective radioimmunoassay for chromogranin A (Chrg A) has been developed to quantitate content, release, and biosynthesis of this secretory protein in neuroendocrine tissues. An antiserum raised against Chrg A from bovine adrenal medulla was found to detect predominantly only the Mr 70-75 kilodalton Chrg A in its native form, allowing the use of this antiserum as a quantitatively specific probe for Chrg A in cell-free extracts of the adrenal medulla and chromaffin cells. Chrg A comprises about 10% of the total protein of the chromaffin cell. It is released in parallel with Met-enkephalin and catecholamines from the bovine chromaffin cell in primary culture in response to nicotine and nicotinic cholinergic agonists. From 14 to 22% of total Chrg A is released from the cell during a 15-min exposure to a maximally stimulatory dose of nicotine (10-100 microM). Chrg A release on nicotinic stimulation is blocked by D-600 and hexamethonium to the same extent as Met-enkephalin and catecholamine release. The parallel time course and percent release of Chrg A and Met-enkephalin indicate that these secretory polypeptides are contained in, and released from, functionally identical cellular compartments. Chrg A and Met-enkephalin pentapeptide sequences are present in the chromaffin cell at a ratio of about 2:1, although Chrg A is far more abundant on a mass basis. Chrg A and Met-enkephalin biosynthesis appear to be differentially regulated within the chromaffin cell, since chronic treatment of cells with nicotine and forskolin causes an elevation of Met-enkephalin pentapeptide without a concomitant elevation of intracellular levels of Chrg A.

Anti-alpha-fodrin inhibits secretion from permeabilized chromaffin cells

Chromaffin cells release catecholamine- and peptide-containing granules by exocytosis, by a mechanism involving movement of secretory granules towards the cell membrane, their apposition to it and the fusion of the granule membrane with the plasma membrane. One of the two subunits of membrane-associated brain spectrin, alpha-fodrin is an actin-binding protein which is found at the periphery of chromaffin cells and may be involved in secretion. Because cultured chromaffin cells can be permeabilized with detergents, giving pores large enough to permit the entry of immunoglobulin molecules, we used permeabilized cells to test the effect of specific antibodies on secretory mechanisms. Incubation of permeabilized cells with polyclonal immunoaffinity-purified monospecific anti-alpha-fodrin antibody or its Fab fragments did not modify basal release but did specifically inhibit Ca2+-induced catecholamine release by exocytosis. Our observations indicate that fodrin and the cytoskeleton participate in the release mechanism.

Dihydropyridine modulation of the chromaffin cell secretory response

Prolonged perfusion of cat adrenal glands with Krebs-bicarbonate solutions containing nicotine, muscarine, or excess K rapidly increased the rate of catecholamine output proportional to the concentrations of secretagogue used. The secretory responses to nicotine or high K reached a peak and declined to almost basal rates of secretion after about 10 min of stimulation. The dihydropyridine Ca channel agonist Bay K 8644 potentiated markedly the secretory responses to 1 microM nicotine and to 17.7 mM K but not to higher concentrations of these secretagogues. The muscarinic response did not decrease with time and was modestly potentiated by Bay K 8644. Similar curves were obtained with 17.7 mM K plus Bay K 8644 and with 59 mM K alone. CGP28392, another agonist, was about 10 times less potent than Bay K 8644 in potentiating the secretory responses to 17.7 mM K. Bay K 8644 also potentiated the release of [3H]noradrenaline evoked by stimulation of cultured bovine adrenal chromaffin cells with 17.7 mM K or 2 microM nicotine but not with higher concentrations of K or nicotine. Dihydropyridine Ca channel antagonists reversed the effects of Bay K 8644 with the following order of potency: niludipine greater than nifedipine = nimodipine greater than nitrendipine. The secretory rates from intact chromaffin cells treated with the Ca ionophores X537A or A23187, or those evoked by Ca-EGTA buffers from digitonin-permeabilized cells, were not affected by Bay K 8644. These results are compatible with the following conclusions: Bay K 8644 selectively potentiates catecholamine secretory responses mediated through the activation of voltage-sensitive Ca channels; during nicotine or high-K stimulation, Ca gains access to the cell interior through a common permeability pathway, the Ca channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of a 190-kD microtubule-associated protein from bovine adrenal cortex

A heat-stable microtubule-associated protein (MAP) with molecular weight of 190,000, termed 190-kD MAP, was purified from bovine adrenal cortex. This MAP showed the same level of ability to promote tubulin polymerization as did MAP2 and tau from mammalian brains. Relatively high amounts of 190-kD MAP could bind to microtubules reconstituted in the presence of taxol. At maximum 1 mol of 190-kD MAP could bind to 2.3 mol of tubulin. 190-kD MAP was phosphorylated by a cAMP-dependent protein kinase prepared from sea urchin spermatozoa and by protein kinase(s) present in the microtubule protein fraction prepared from mammalian brains. The maximal numbers of incorporated phosphate were approximately 0.2 and approximately 0.4 mol per mole of 190-kD MAP, respectively. These values were lower than that of MAP2, which could be heavily phosphorylated by the endogenous protein kinase(s) up to 5 mol per mole of MAP2 under the same assay condition. 190-kD MAP had no effects on the low-shear viscosity of actin and did not induce an increase in turbidity of the actin solution. It was also revealed that 190-kD MAP does not cosediment with actin filaments. These data clearly show that, distinct from MAP2 and tau, this MAP does not interact with actin. Electron microscopic observation of the rotary-shadowed images of 190-kD MAP showed the molecular shape to be a long, thin, flexible rod with a contour length of approximately 100 nm. Quick-freeze, deep-etch replicas of the microtubules reconstituted from 190-kD MAP and brain tubulin revealed many cross-bridges connecting microtubules with each other.

Phosphorylation and dephosphorylation of chromaffin cell proteins in response to stimulation

Stimulation of bovine chromaffin cell in culture changed (increased or decreased) the phosphorylation state of several proteins as examined by 32P incorporation. Enhanced phosphorylation of 22 protein bands as well as increased dephosphorylation of a 20.4 kilodaltons protein band was observed when extracts of cultured chromaffin cells stimulated by either acetylcholine or high K+ were subjected to mono-dimensional gel electrophoresis. For several protein bands, the degree of phosphorylation was larger in cells stimulated by acetylcholine than in those challenged by a depolarizing concentration of K+. The most affected phosphoproteins have apparent molecular weights of 14,800, 29,000, 33,000, 57,000 (tubulin subunit), 63,000 (tyrosine hydroxylase subunit) and 94,000. The presence of a low extracellular calcium concentration (0.5 mM Ca2+ plus 15 mM Mg2+) in the incubation medium inhibited (38-100%) the acetylcholine-evoked increases in protein phosphorylation observed previously for 18 protein bands. Trifluoperazine at the concentration required for 50% inhibition of acetylcholine-induced catecholamine release decreases (33-100%) the stimulation-induced phosphorylation in all polypeptides, with the exception of the 14.8 kilodaltons and the dephosphorylated 20.4 kilodaltons components which were not affected. Two-dimensional gel electrophoresis analysis revealed that exposure of chromaffin cells to acetylcholine produced two types of effect on protein phosphorylation: activation of protein kinase activities affecting about 30 polypeptides; activation of protein phosphatase activities resulting in the dephosphorylation of about 40 polypeptides, most of them appearing as minor phosphoproteins, with the exception of the alpha-subunit of pyruvate dehydrogenase and the 20.4 kilodaltons polypeptide. On the basis of their molecular properties (molecular weight and pI) and their abundance in chromaffin cells, the 80 kilodaltons phosphoprotein which focused at pI 4.8 and the 117.5 kilodaltons phosphoprotein which focused at pI 5.0 were identified as chromogranins A and B, respectively. The relationship between acetylcholine-induced protein phosphorylation (or dephosphorylation) and catecholamine secretion was also investigated. The time course of protein phosphorylation (or dephosphorylation) paralleled or preceded [3H]noradrenaline release for 16 phosphoproteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Assembly and characterisation of a multi-component cytoskeletal gel from adrenal medulla

Incubation of bovine adrenal medullary cytoplasmic extracts results in the formation of three-dimensional supramolecular gels. Ultrastructurally, the gels display a network of fibres similar in appearance to the cytoskeleton within intact chromaffin cells. Analysis of the protein composition using both electrophoretic and immunoblotting techniques indicates that the gels are composed exclusively of cytoskeletal elements; microfilaments, microtubules and intermediate filament proteins have been identified as having a number of actin-associated proteins. Among the latter class of components the following polypeptides have been identified: filamin (300 kDa), fodrin (240 kDa), a 235 kDa polypeptide, myosin (200 kDa), caldesmon (70 kDa) and tropomyosins (39 kDa). All of these polypeptides co-sedimented with F-actin when gels were assembled in the absence of Ca2+. When gelation was performed in the presence of 10 microM Ca2+ actin, the 235 kDa polypeptide, 70 kDa caldesmon and tropomyosin were all absent from the gels. These results may suggest that the 235 kDa polypeptide, 70 kDa caldesmon and tropomyosins could act either individually or as a functional regulatory unit in controlling the Ca2+-activated reorganisation of the actin network in the cytoplasmic gels.

Surface expression of neural cell adhesion molecule in cultured bovine paraneurones: immunogold and immunoperoxidase methods compared

The D2 neural cell adhesion molecule immunolabelling patterns of cultured bovine chromaffin cells are compared at the ultrastructural level, using the indirect immunohistochemical method with the secondary antibody labelled with either 17 or 5 nm gold particles or horseradish peroxidase (HRP). With HRP-conjugated antibody an apparently continuous surface staining was produced, while with 17 nm gold particles relatively large areas of membrane remained unlabelled; 5 nm particles gave a pattern more closely resembling the localization obtained with HRP. These differences are explained by differences in steric hindrance inherent to each method.

Secretory cell actin-binding proteins: identification of a gelsolin-like protein in chromaffin cells

Chromaffin cells, secretory cells of the adrenal medulla, have been shown to contain actin and other contractile proteins, which might be involved in the secretory process. Actin and Ca++-sensitive actin-binding proteins were purified from bovine adrenal medulla on affinity columns using DNase-I as a ligand. Buffers that contained decreasing Ca++ concentrations were used to elute three major proteins of 93, 91, and 85 kD. The bulk of the actin was eluted with guanidine-HCl buffer plus some 93- and 91-kD proteins. These Ca++-sensitive regulatory proteins were shown to inhibit the gelation of actin using the low-shear falling ball viscometer and by electron microscopy. Actin filaments were found to be shortened by fragmentation. Using antibody raised against rabbit lung macrophage gelsolin, proteolytic digestion with Staphylococcus V8 protease and two-dimensional gel electrophoresis, the 91-kD actin-binding protein was shown to be a gelsolin-like protein. The 93-kD actin-binding protein also showed cross-reactivity with anti-gelsolin antibody, similar peptide maps, and a basic-shift in pHi indicating that this 93-kD protein is a brevin-like protein, derived from blood present abundantly in adrenal medulla. Purification from isolated chromaffin cells demonstrated the presence of 91- and 85-kD proteins, whereas the 93-kD protein was hardly detectable. The 85-kD protein is not a breakdown product of brevin-like or gelsolin-like proteins. It did not cross-react with anti-gelsolin antibody and showed a very different peptide map after mild digestion with V8 protease. Antibodies were raised against the 93- and 91-kD actin-binding proteins and the 85-kD actin-binding protein. Antibody against the 85-kD protein did not cross-react with 93- and 91-kD proteins and vice versa. In vivo, the cytoskeleton organization of chromaffin secretory cells is not known, but appears to be under the control of the intracellular concentration of free calcium. The ability of calcium to activate the gelsolin-like protein, and as shown elsewhere to alter fodrin localization, provides a mechanism for gel-sol transition that might be essential for granule movement and membrane-membrane interactions involved in the secretory process.

Immunofluorescence demonstration of tubulin and actin in estrogen-induced rat prolactinoma cells in vitro. Alteration of their distribution after bromocriptine, colchicine and cytochalasin B treatments

Cultured cells in vitro from estrogen-induced rat prolactin-secreting adenomas (prolactinomas) were examined by indirect immunofluorescence microscopy for the distribution of cytoskeletal proteins and alterations of cytoskeleton after treatment with bromocriptine, colchicine and cytochalasin B (CB). After 8 days in culture, prolactinoma cells were well expanded and developed cytoplasmic processes were seen. The cytoplasmic microtubules were observed as fine reticular networks radiating from perinuclear portions toward the cell periphery when decorated with an antibody against tubulin. On the other hand, the actin filaments showed diffuse and spotty distribution when detected with an anti-actin antibody. Contaminated fibroblasts showed a reticular distribution of microtubules and a parallel array of actin cables which corresponds to "stress fibers" throughout the cytoplasm. After treatment with bromocriptine, the reticular distribution of microtubules in prolactinoma cells changed into a coarse and sparse pattern, which was identical with the changes in the distribution of tubulin after treatment with colchicine. On the other hand, distribution of actin was not affected by bromocriptine. Bromocriptine treatment did not alter the distribution of microtubules and actin filaments in fibroblasts, whereas colchicine changed the distribution of microtubules in both prolactinoma cells and fibroblasts. CB treatment changed the localization of actin filaments in both kinds of cells. These in vitro studies indicated bromocriptine would selectively affect the cytoplasmic microtubular system of prolactinoma cells.

Reorganization of alpha-fodrin induced by stimulation in secretory cells

Spectrin is an ubiquitous protein composed of heterodimers with alpha and beta subunits. It was first described in erythrocyte cell membranes (see ref. 1 for review) and subsequently in brain, intestinal brush borders, kidney, liver and adrenals. Brain spectrin (fodrin) alpha-subunit, responsible for actin binding, has a relative molecular mass (Mr) of 240,000, whereas the beta-subunit, involved in membrane attachment, has an Mr of 235,000 (refs 1, 3, 9-13). The membrane of secretory granules from adrenal chromaffin cells membrane of secretory granules from adrenal chromaffin cells increases the viscosity of F-actin solution, and spectrin-like protein is associated with storage granule and plasma membranes. Here, we report the localization of fodrin in secretory cells using monospecific antibodies against the alpha-subunit of fodrin using indirect immunofluorescence. We find that the alpha-subunit forms an intensely stained continuous ring in the subplasmalemmal region of resting chromaffin cells. On stimulation of the cell with nicotine, high potassium or ionophores in the presence of calcium, fodrin forms patches. This aggregation is inhibited by trifluoperazine, hence the entrance of calcium into cells following cell depolarization seems to be the calmodulin-dependent stimulus initiating patch formation.

Effect of taxol on secretory cells: functional, morphological, and electrophysiological correlates

The effect of 0.5-1.0 microM taxol, a potent promoter of microtubule polymerization in vitro, was studied on the secretory activity of chromaffin cells of the adrenal medulla. Taxol was found to have a dual effect: the long-term effect (after a 1-h incubation) of taxol was to induce almost complete inhibition of catecholamine release, whereas after a short incubation (10 min) a massive, nicotine-independent release of catecholamine was produced. From results obtained using the patch-clamp technique to study the Ca++-dependent K+ channels (Ic channels), it was possible to conclude that taxol probably provokes an augmentation of free [Ca++]i in the cytoplasm, values increasing from 10(-8) M at rest to several 10(-7) M. The increased spontaneous release of stored neurohormones and the increased frequency of opening of Ic channels occur simultaneously and could both originate from a rise of [Ca++]i upon taxol addition. Immunofluorescence and ultrastructural studies showed that 13-h taxol treatment of chromaffin cells led to a different distribution of secretory organelles, and also to microtubule reorganization. In treated cells, microtubules were found to form bundles beneath the cell membrane and, at the ultrastructural level, to be packed along the cell axis. It is concluded that in addition to its action on microtubules, the antitumor drug taxol has side effects on the cell secretory activity, one of them being to modify free [Ca++]i.

Presence of microtubule-associated protein 2 in chromaffin cells

We have examined bovine adrenal chromaffin cells in culture for the presence of the microtubule-associated protein 2. Chromaffin cells could be identified in culture on the basis of their staining with antibodies directed against secretory granule proteins. Using immunoperoxidase staining microtubule-associated protein 2 immunoreactivity was demonstrated to be present in chromaffin cells but not fibroblasts in culture. Microtubule-associated protein 2 immunoreactivity was present in the cell body, processes and varicosities of the chromaffin cells. Microtubule-associated protein 2 polypeptides were shown to be present in an adrenal medullary homogenate but not chromaffin granule membranes by immunoblotting. The results indicate that the neuronal cytoskeletal polypeptide microtubule-associated protein 2 is present in adrenal chromaffin cells. The presence of microtubule-associated protein 2 in both neurons and chromaffin cells may be related to their common embryonic origin.

Chronobiological studies on the nucleolus

Chronobiological studies on the nucleolus were performed, using stereological analysis at the electron microscopic level, on different cell types in permanent interphasic state, in rats submitted to various lighting regimen. During the dark span (12L/12D): (1) in sympathetic neurons of superior cervical ganglion circadian changes in nucleolar organization were characterized by an increase in volumes of the nucleolus and each of its components, namely, fibrillar centres, dense fibrillar, granular and vacuolar components; (2) concerning the fibrillar centres, regarded as the interphasic counterpart of nucleolar organizing regions (NORs), the most striking fact, only observed in sympathetic neurons, is the occurrence of a single large-type fibrillar centre, accompanied by small-type fibrillar centres which are present throughout the 24-hr period; (3) the overall increase in volume of fibrillar centres was shown to correspond to a marked drop in the number (up to 4 fold) of small-type fibrillar centres, the unit volume of which (0.01 mum3) remaining unchanged over the 24-hr period and to an increase in size of a large-type fibrillar centre, the volume of which is 100 fold greater than the latter and (4) cytochemical studies showed that the Ag-NOR proteins exhibit a marked increase in amount, suggesting a circadian rhythmicity of these nucleolar proteins. These results, discussed in the light of our current understanding of the nucleolus, briefly summarized in this paper, suggest that the circadian rhythm of the nucleolus and of its components is correlated with circadian rhythms in both transcriptional activity and processing of preribosomes. Analogies between sympathetic neurons and the two other cell types studied, namely, chromaffin cells of adrenal medulla and vagal sensory neurons of nodose ganglion, led to the conclusion that rhythmicity is a fundamental characteristic of the nuclear structure devoted to ribosome biogenesis. Attention is focused on the superior cervical ganglion in which amplitude of nucleolar rhythms are greater and in which fibrillar centres exhibit a particular pattern. These results are discussed with regard to the role played by this sympathetic paravertebral ganglion which is known to regulate circadian rhythmic activities of the rat pineal gland. The persistence of these nucleolar rhythms in continuous lighting, as demonstrated in sympathetic superior cervical ganglion neurons, provide evidence that they are endogenously generated. The intrinsic factors underlying these rhythms in morpho-functional organization of the nucleolus are yet unknown.(ABSTRACT TRUNCATED AT 400 WORDS)