Anti-myosin stains chromaffin cells

Myosins II and V in chromaffin cells: myosin V is a chromaffin vesicle molecular motor involved in secretion

The presence of myosin II and V in chromaffin cells and their subcellular distribution is described. Myosin II and V distribution in sucrose density gradients showed only a strong correlation between the distribution of myosin V and secretory vesicle markers. Confocal microscopy images demonstrated colocalization of myosin V with dopamine beta-hydroxylase, a chromaffin vesicle marker, whereas myosin II was present mainly in the cell cortex. Cell depolarization induced, in a Ca2+ and time-dependent manner, the dissociation of myosin V from chromaffin vesicles suggesting that this association was not permanent but determined by secretory cycle requirements. Myosin II was also found in the crude granule fraction, however, its distribution was not affected by cell depolarization. Myosin V head antibodies were able to inhibit secretion whereas myosin II antibodies had no inhibitory effect. The pattern of inhibition indicated that these treatments interfered with the transport of vesicles from the reserve to the release-ready compartment, suggesting the involvement of myosin V and not myosin II in this transport process. The results described here suggest that myosin V is a molecular motor involved in chromaffin vesicle secretion. However, these results do not discard an indirect role for myosin II in secretion through its interaction with F-actin networks.

Molecular motors involved in chromaffin cell secretion

Neurosecretory cells, including chromaffin cells, possess a mesh of filamentous actin underneath the plasma membrane. It has been proposed that filamentous actin network separates the secretory vesicles into two compartments: the reserve pool and the release-ready vesicle pool. Disassembly of chromaffin cell cortical filamentous actin in response to stimulation allows the movement of vesicles from the reserve pool into the release-ready vesicle pool. Electron microscopy of cytoskeletons revealed the presence of polygonal areas almost devoid of actin filaments in stimulated cells. The percentage of stimulated cells showing disrupted cytoskeleton correlates well with the increase in secretion in these cells. Fine filaments also remain in these areas of disassembly, and these reacted with actin antibodies, as demonstrated by immunogold staining. In addition, the movement of vesicles between pools requires Ca(2+) and ATP, a condition for activation of a molecular motor. Confocal microscopy images demonstrated colocalization of myosin Va with dopamine-beta-hydroxylase. Cell depolarization induced the dissociation of myosin Va from chromaffin vesicles. 2,3-Butadione-2-monoxime (BDM), an inhibitor of myosin ATPase, inhibited secretion, suggesting a blockage for chromaffin vesicle transport between the reserve pool and the release-ready vesicle pool. On the other hand, myosin II subcellular distribution was not affected by cell depolarization. Confocal microscopy images show myosin II to be localized in the cell cortex and in some perinuclear structures. Chromaffin vesicles were not stained by myosin II antibody.

Mastoparan blockade of currents through Ca(2+)-activated K+ channels in bovine chromaffin cells

The action of mastoparan (a wasp venom peptide) on "maxi" Ca(2+)-activated K+ channels was studied in excised inside-out patch recordings from cultured bovine chromaffin cells, under normal conditions (160 mM K+ inside, 154 mM Na+ outside). Mastoparan, when applied on the intracellular side of the membrane reduced the open channel probability in a concentration dependent manner. Changes in the channel kinetics were complex. The histograms of the open dwell times were all described by either one or two exponentials. Mastoparan shortened the mean duration of the major (long) component and to a lesser extent the minor (short) component. Closed dwell times, were described by three exponentials. While the short (major) component was prolonged by mastoparan, and the intermediate component was unaffected, the long component was shortened. Overall mean closed times were prolonged. The changes in channel kinetics could only partly be explained by a channel-blocking mechanism, even when assuming that mastoparan acts as both an intermediate and a slow channel blocker suggesting that it affects gating mechanism. The fact that mastoparan is a calmodulin inhibitor and a G-protein activator raises the possibility that in bovine chromaffin cells, either the membrane-bound calmodulin or a G-protein, plays a role in the modulation of Ca(2+)-activated K+ channels.

Choline blockage of currents through Ca(2+)-activated K+ channels in bovine chromaffin cells

The action of choline on "maxi" Ca(2+)-activated K+ channels was studied in excised patches of bovine chromaffin cell membranes. Choline (20-70 mM) applied to the internal surface of the membrane reduced the single channel current amplitudes, which can be explained by a fast channel block. The block is concentration- and voltage-dependent and is rapidly and completely reversed upon washout. The block becomes progressively greater with depolarization. The estimates of blocking parameters vary from channel to channel but appear to fall in two groups. A larger group (two-thirds of cases) with moderate affinity [KD(0) = 88.5 mM] and low voltage dependence (delta = 0.26) and a smaller group (one-third of cases) with very low affinity (KD = 306 mM) and moderate voltage dependence (delta = 0.59). The open state probability appears not to be affected at any choline concentration (up to 70 mM) or membrane potential (from -20 to +60 mV) studied, suggesting that choline does not affect the channel gating kinetics. Since the affinity of the choline block is low to moderate, the intracellular choline is not expected to alter the current flow through "maxi" Ca(2+)-activated K+ channels unless the choline concentration close to the protoplasmic membrane is much higher than the mean cellular concentration.

Adrenal phenylethanolamine N-methyltransferase induction in relation to glucocorticoid receptor dynamics: evidence that acute exposure to high cortisol levels is sufficient to induce the enzyme

Glucocorticoids (GCs) are thought to regulate, in a permissive fashion, the basal activity of adrenal medullary phenylethanolamine N-methyltransferase (PNMT). However, it is unclear whether a large short-term increase in GC release, such as occurs during an acute stress response, may also play a role in PNMT regulation. The present study investigated how the GC influence over PNMT activity varies in relation to dynamic changes in the hormone-receptor signal. Using [3H]dexamethasone (DEX) and [3H]RU 28362 as radioligands, we have confirmed the presence of GC receptors in bovine adrenal medullary cells. A concentration-dependent decline in soluble GC receptor sites and an increase in nuclear uptake of [3H]DEX were found in response to GC levels as low as 5 x 10(-8) M. The loss of soluble sites plateaued between 5 x 10(-8) and 10(-6) M cortisol, with further losses occurring at 10(-5) and at 10(-4) M. The functional consequence of GC receptor binding was confirmed by measuring PNMT activity following 3-day exposure to cortisol. The pattern of PNMT induction was similar to that seen with GC receptor occupancy; at cortisol concentrations between 10(-8) and 10(-5) M, PNMT induction was at a plateau, with a further increase in activity at 10(-4) M. The increase in PNMT activity following 3-day exposure to low (10(-7) M) and high (5 x 10(-5), 10(-5) M) cortisol was blocked by the GC receptor antagonist RU 38486, suggesting a GC receptor-mediated event. Finally, a short (2 h) pulse of GC, which mimics the time course of physiological elevation of GC following acute stress, elevated adrenal medullary PNMT activity measured 3 days later. Therefore, our results provide novel evidence that short-term exposure of adrenal medullary cells to high cortisol levels can elevate PNMT activity.

Dopamine release from bovine adrenal medullary cells in culture

The present study tested whether release of dopamine from isolated bovine adrenal medullary cells in culture could be stimulated or inhibited by secretagogues and modulators known to affect noradrenaline and adrenaline release from adrenal medullary chromaffin cells. K+ depolarization or activation of voltage-sensitive Na+ channels by veratridine both stimulated dopamine release. Ca2+-dependent dopamine release was also stimulated by the mixed nicotinic-muscarinic agonist, carbachol. Carbachol-induced dopamine release was inhibited by a nicotinic but not by a muscarinic antagonist and dopamine release was also stimulated by a selective nicotinic agonist, 1,1-dimethyl-4-phenyl-piperazinium. Carbachol-induced dopamine release was inhibited by substance P and by neuropeptide Y. Histamine also stimulated dopamine release, while angiotensin II and glutamate produced no significant stimulation of dopamine release. Noradrenaline and adrenaline were released in response to the above agents with a profile almost identical to that of dopamine. The results indicate that dopamine can be directly released from adrenal medullary cells in response to stimulation of those cells and suggest that the dopamine release originates from chromaffin cells similar or identical to those storing noradrenaline and adrenaline. A possible role for dopamine, released from adrenal chromaffin cells, in modulating catecholamine release from the chromaffin cells and/or contributing to circulating plasma dopamine is discussed.

Effect of quinine on the release of catecholamines from bovine cultured chromaffin cells

1. The effects of quinine on catecholamine release from cultured bovine chromaffin cells were studied. 2. Quinine (25-400 microM) produced a dose-related inhibition of catecholamine release in response to depolarizing concentrations (12.5-50 mM) of K+. 3. The inhibition of the secretory response to high K+ produced by quinine decreased with the increase in the extracellular concentration of Ca2+. 4. Stimulation of cultured chromaffin cells with 50 mM K+ produced a significant increase in Ca2+ influx. In the presence of 100 microM quinine a 54% inhibition of the K(+)-induced Ca2+ influx was observed. 5. Quinine treatment of chromaffin cell cultures produced a small but significant decrease in membrane resting potential and a less pronounced depolarization in response to 50 mM K+. 6. The results suggest that the inhibition of the K(+)-evoked release of catecholamines produced by quinine is at least partly due to a decrease in Ca2+ influx. Ca2+ influx is lower because quinine reduces the sensitivity of the membrane potential to changes in extracellular K+ but direct effects of quinine on Ca2+ channels cannot be excluded.

Phosphorylation of myosin light chain from adrenomedullary chromaffin cells in culture

The myosin-light-chain (MLC) phosphorylation accompanying catecholamine release in chromaffin cells was investigated with the objective of assessing the possible role of this contractile protein in catecholamine secretion. The electrophoretic characteristics of adrenomedullary MLC were determined by immunochemical techniques using two different specific antibodies. The identified 22 kDa phosphoprotein was mainly present in the cytosol, as demonstrated by ultracentrifugation and immunocytochemical analysis. A part of this protein was located on, or close to, the plasma membrane. Cell stimulation by secretagogues resulted in a Ca2(+)-dependent 32P incorporation into MLC, the time course of this process being related to catecholamine release. These findings were supported by a two-dimensional gel-electrophoretic analysis by which means this protein was resolved into two acidic forms. A role for Ca2(+)-calmodulin and Ca2(+)-phospholipid kinases in adrenomedullary MLC phosphorylation is reported. The results obtained suggest a regulatory role for such a protein in the underlying exocytotic event.

Effects of the catecholaminergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) on adrenal chromaffin cells in culture

N-(2-Chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) is an inhibitor of noradrenaline uptake and a neurotoxin known to deplete noradrenaline levels with little effect on dopamine, serotonin or adrenaline in the central nervous system. The present study tested the effects of DSP-4 on catecholamine uptake, release and content in cultures of isolated bovine adrenal chromaffin cells. DSP-4 selectively inhibited the acute uptake of [3H]noradrenaline with little or no effect on [3H]adrenaline or [3H]dopamine uptake. In cultures preloaded with [3H]catecholamines, DSP-4 stimulated the release of [3H]noradrenaline and, to a small extent, also [3H]adrenaline and [3H]dopamine. However, the drug did not stimulate the release of appreciable amounts of endogenous adrenaline, noradrenaline or dopamine. A high concentration of DSP-4 inhibited the carbachol-stimulated release of adrenaline, noradrenaline and dopamine from the cells. Following a 1-hr exposure to the drug, DSP-4 decreased adrenaline, noradrenaline and dopamine levels in the cells with no gross morphologic changes in the cells. Reductions in adrenaline and noradrenaline levels were almost equal in magnitude, while dopamine was depleted to a somewhat greater extent under some conditions. Longer exposure to DSP-4 resulted in morphological changes in the cells, suggesting that the drug is also toxic to chromaffin cells in culture.

Detection of low molecular mass GTP-binding proteins in chromaffin granules and other subcellular fractions of chromaffin cells

A homogenate of purified chromaffin cells was fractionated, after removal of the nuclear fraction, by sucrose density gradient ultracentrifugation. The presence and subcellular localization of low molecular mass GTP-binding proteins was explored by incubation of blots of proteins from different subcellular fractions with [alpha-32P]GTP in the presence of Mg2+. The fractions enriched in intact chromaffin granule markers, i.e. catecholamines, chromogranin A, chromogranin B and cytochrome b-561 were also enriched in labelled GTP-binding proteins. Two major labelled components of 23 and 29 kDa were rapidly detected by autoradiography. Traces of 26 and 27 kDa components were also present. These components were detectable in both plasma and granule membranes. In addition to these components, the cytosolic fraction contained another GTP-binding protein of about 20 kDa. Binding of [alpha-32P]GTP was specific and dependent on Mg2+. By analogy to the findings reported in non-mammalian systems, the observations described here suggest the involvement of low molecular mass GTP-binding proteins in the chromaffin cell secretory process.

Calmodulin-binding proteins in chromaffin cell plasma membranes

Calmodulin-binding proteins present in chromaffin cell plasma membranes were isolated and directly compared with calmodulin-binding proteins present in chromaffin granule membranes. Chromaffin cell plasma membranes were prepared using Cytodex 1 microcarriers. Marker enzyme studies on this preparation showed a nine- to 10-fold plasma membrane enrichment over cell homogenates and a low contamination of these plasma membranes by subcellular organelles. Plasma membranes prepared in this manner were solubilized with Triton X-100 and applied to a calmodulin-affinity column in the presence of calcium. Several major calmodulin-binding proteins (240, 105, and 65 kilodaltons) were eluted by an EGTA-containing buffer. 125I-Calmodulin overlay experiments on nitrocellulose sheets containing both chromaffin plasma and granule membranes showed that these two membranes have several calmodulin-binding proteins in common (65, 60, 53, and 50 kilodaltons), as well as unique calmodulin-binding proteins (34 kilodaltons in granule membranes and 240 and 160 kilodaltons in plasma membranes). The 65-kilodalton calmodulin-binding protein present in both membrane types was shown to consist of two isoforms (pI 6.0 and 6.2) by two-dimensional gel electrophoresis. Previous experiments from our laboratory, using two monoclonal antibodies (mAb 30 and mAb 48) specific for a rat brain synaptic vesicle membrane protein (p65), showed that the monoclonal antibodies reacted with a 65-kilodalton calmodulin-binding protein present in at least three neurosecretory vesicles (chromaffin granules, neurohypophyseal granules, and rat brain synaptic vesicles). When these monoclonal antibodies were tested on chromaffin cell plasma membranes and calmodulin-binding proteins isolated from these membranes, they recognized a 65-kilodalton protein. These results indicate that an immunologically identical calmodulin-binding protein is expressed in both chromaffin granule membranes (as well as other secretory vesicle membranes) and chromaffin cell plasma membranes, thus suggesting a possible role for this protein in granule/plasma membrane interaction.

Quinine blockade of currents through Ca2+-activated K+ channels in bovine chromaffin cells

1. The blocking action of quinine of Ca2+-activated K+ channels was studied in excised inside-out patch recordings from cultured bovine chromaffin cells. Under normal ionic conditions (160 mM-K+ inside, 154 mM-Na+ outside), the unitary conductances measured between -20 and +40 mV were between 95 and 210 pS. 2. Quinine applied on the intracellular side of the membrane in micromolar concentrations chopped the unitary K+ currents into bursts of brief openings. These 'flickery bursts' appear to arise from discrete blocking and unblocking transitions. 3. Open and closed times within such flickery bursts were exponentially distributed suggesting a simple reaction between quinine and an open channel. 4. The blocking rate varied linearly with the concentration of quinine (rate coefficient 1.6 x 10(6) M-1 s-1). The unblocking rate was high (greater than 5000 s-1) and essentially independent of the quinine concentration. 5. The blocking rate was voltage dependent and increased with hyperpolarization which suggests that quinine acts predominantly or exclusively from the extracellular side of the membrane. The unblocking rate appeared to be independent of the membrane potential. 6. The probability of the open state was not altered by quinine indicating that quinine did not interfere directly with the gating process. 7. The total current carried by K+ ions was reduced by quinine only marginally (less than 10%) even at high quinine concentrations (1.5 mM). Moreover the reduction of the total current was also essentially voltage independent. 8. Quinine is clearly a very poor blocker. Poor block occurs, however, not only because of the brevity of the closed periods but presumably also because the channel can be closed only when it is not blocked. Only when the probability of channel opening (p) was high (greater than 0.85), i.e. when the channel's gate was predominantly open, did the flickery block appear to reduce the total current appreciably.

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)

Studies on the uptake and release of propranolol and the effects of propranolol on catecholamines in cultures of bovine adrenal chromaffin cells

Uptake and release of [3H]l-propranolol and the effects of propranolol on the uptake and release of [3H]norepinephrine were studied in cultures of isolated bovine adrenal chromaffin cells. [3H]l-Propranolol uptake increased with increasing [3H]l-propranolol concentration from 10(-7) M to 10(-3) M and was not saturable in this concentration range. [3H]l-Propranolol uptake was equally inhibited by l- and d-propranolol, indicating that the uptake is not stereoselective. [3H]l-Propranolol uptake differed from [3H]norepinephrine uptake in two respects: [3H]l-propranolol uptake was 44-50 times greater than [3H]norepinephrine uptake at early non-equilibrium time periods, and [3H]l-propranolol uptake was not Na+ dependent and was not inhibited by desipramine, indicating that [3H]l-propranolol is not taken up by the biogenic amine transport system. In cells preloaded with [3H]l-propranolol, two agents, veratridine and tyramine, stimulated an increased release of [3H]l-propranolol into the medium. However, veratridine-induced [3H]l-propranolol release was inhibited only slightly by the Na+ channel blocker tetrodotoxin, and tyramine-induced [3H]l-propranolol release was not inhibited by desipramine. In addition, K+, carbachol and the physiological mediator of adrenal catecholamine release, acetylcholine, failed to evoke [3H]l-propranolol release. Therefore, it is unlikely that propranolol is released in response to physiological stimulation of adrenal chromaffin cells in animals administered propranolol in vivo. l-Propranolol inhibited [3H]norepinephrine uptake by chromaffin cells with an IC50 for l-propranolol of 5 X 10(-6) M; d-propranolol was equally potent for this effect at lower propranolol concentrations. By themselves, neither l- nor d-propranolol had any effect on [3H]norepinephrine release from the cells. However, l-propranolol inhibited carbachol-induced [3H]norepinephrine release with an IC50 for l-propranolol of 5 X 10(-7) M to 10(-6) M. At these lower concentrations, d-propranolol had no effect on carbachol-induced [3H]norepinephrine release, indicating that the inhibition by l-propranolol may be mediated via beta-adrenoceptors on chromaffin cells.

Effects of substance P on carbachol-stimulated 45Ca2+ uptake into cultured adrenal chromaffin cells

Substance P is known to modulate acetylcholine-induced catecholamine release from adrenal chromaffin cells. To investigate the mechanisms involved in this modulation, the present study examined the effects of substance P on net 45Ca2+ fluxes in cultures of bovine adrenal chromaffin cells. Two effects of substance P were observed: (1) Substance P inhibited carbachol-induced 45Ca2+ uptake and 45Ca2+ efflux and (2) substance P protected against desensitization of carbachol-induced 45Ca2+ uptake and 45Ca2+ efflux. Thus substance P modulates two other cholinergic responses, 45Ca2+ uptake and 45Ca2+ efflux, in a manner similar to its modulation of catecholamine release. The results also indicate that substance P's inhibition of net carbachol-induced 45Ca2+ uptake is due to inhibition of 45Ca2+ uptake rather than enhancement of 45Ca2+ efflux. Substance P almost completely inhibited carbachol-induced 45Ca2+ uptake in both Na+-containing and Na+-free media, suggesting that substance P can inhibit the uptake of 45Ca2+ induced by carbachol regardless of whether 45Ca2+ is taken up through voltage-sensitive or acetylcholine receptor-linked channels. However, substance P produced only a small inhibition of K+-induced 45Ca2+ uptake, indicating that substance P does not interact directly with voltage-sensitive Ca2+ channels. In addition, substance P's inhibition of carbachol-induced 45Ca2+ uptake was noncompetitive with respect to Ca2+, were unable to overcome substance P's inhibition of [3H]-norepinephrine ( [3H]NE) release. It is concluded that substance P does not interact directly with Ca2+ channels in bovine adrenal chromaffin cells.

Acetylcholine synthesis by adult bovine adrenal chromaffin cell cultures

Adrenal chromaffin cells normally synthesize and release catecholamines. In the present study, [3H]acetylcholine synthesis and another characteristic of cholinergic neurons, [3H]choline uptake, were studied in cultures of adult bovine adrenal chromaffin cells. Chromaffin cell cultures took up [3H]choline from the medium and acetylated the [3H]choline to form [3H]acetylcholine. The rate of [3H]acetylcholine synthesis increased after 19 days in culture and continued to increase up to 28 days in culture. [3H]Acetylcholine synthesis could be increased by stimulating the cells with a depolarizing concentration of K+. The ability for K+ to stimulate synthesis of [3H]acetylcholine developed only after 28 days in culture. [3H]Choline was taken up by the cultures through a single mechanism with a high (to intermediate) affinity for choline. [3H]Choline uptake was enhanced by Na+ omission in day-14 cultures, but was at least partially Na+-dependent in day-29 cultures. Hemicholinium-3 (IC50 less than 10 muM) inhibited [3H]choline uptake into chromaffin cell cultures. It is concluded that bovine adrenal chromaffin cells, maintained in culture, are able to exhibit cholinergic properties and this capacity is retained even by the mature adult cell.

A technique for the microinjection of macromolecules into viable chromaffin cells in culture

A technique is described by which macromolecules can be microinjected into chromaffin cells in monolayer culture. This technique employs erythrocyte ghosts as the vehicles for microinjection, phytohemagglutinin, a plant lectin, as an attachment agent, and polyethylene glycol as the fusagen. High erythrocyte ghost-chromaffin cell fusion indices have been obtained, with an average of 46.2 +/- 1.1% (n = 14) of the total chromaffin cell population efficiently injected. Cell viability is well maintained during and after fusion with an average cell loss of 12 +/- 0.4% (n = 14) of the total cell population. The functional parameters which characterize the chromaffin cells in culture are unaltered after fusion-induced microinjection. The endogenous catecholamine content, the uptake of exogenous catecholamines via the high-affinity uptake mechanism for catecholamines, as well as the cell's response to various secretagogues remain unchanged. This procedure which allows a large number of cultured cells to be injected rapidly without significant loss of cell viability will aid in the study of the molecular and cell biology in this system.

Purine nucleotide synthesis in adrenal chromaffin cells

The synthesis of purine nucleotides from the salvage precursors adenine and adenosine, and from the de novo precursors formate and glycine, was studied in isolated adrenal chromaffin cells. Both [8-14C]adenine and [8-14C]adenosine from extracellular medium are effectively incorporated into intracellular nucleotides. [14C]Formate and [U-14C]glycine are also incorporated, but de novo synthesis is clearly lower than synthesis from salvage precursors, although similar to de novo synthesis in liver. The enzymes responsible for adenine and adenosine salvage, adenine phosphoribosyltransferase and adenosine kinase, were purified about 1,500-fold. Both enzymes are mainly cytosolic and exhibit a similar molecular weight of around 42,000. The results suggest that chromaffin cells can replenish their intracellular nucleotides lost during the secretory event by an active synthesis from salvage and de novo precursors.

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.

Presence of tropomyosin in adrenal chromaffin cells and its association with chromaffin granule membranes

The presence of tropomyosins in adrenal chromaffin cells was demonstrated by immunoperoxidase staining of cultured chromaffin cells by an anti-tropomyosin antibody. In immunoblotting the antibody labelled polypeptides of Mr 39 000, 36 500 and 31 000 in 100 000 X g supernatants and heat-stable fractions of adrenal medulla. The adrenal medullary tropomyosins did not comigrate with smooth muscle tropomyosins. The 39-kDa and 31-kDa polypeptides comigrated with polypeptides labelled by anti-tropomyosin in brain supernatants. Chromaffin granule membranes possessed a 39-kDa polypeptide that was labelled by anti-tropomyosin.

Microinjection of calmodulin antibodies into cultured chromaffin cells blocks catecholamine release in response to stimulation

Polyclonal monospecific antibodies raised in sheep against rat testis calmodulin demonstrated cross-reactivity with bovine adrenal medullary chromaffin cell calmodulin. This antibody immunoprecipitated a [35S]methionine-labelled protein from chromaffin cell extracts prepared from [35S]methionine prelabelled cells that comigrated on a sodium dodecylsulfate gel electrophoresis system with calmodulin. In addition, an excess of non-radioactive exogenous calmodulin was shown to readily compete with this labelled endogenous protein for the antibodies' binding sites. Erythrocyte ghosts were used as vehicles for microinjecting either preimmune immunoglobulin G or anti-calmodulin immunoglobulin G into chromaffin cells following a polyethylene glycol-induced cell fusion procedure. The efficiency of ghost cell fusion was monitored and found to be 43.6 +/- 1% (n = 33). Cell morbidity subsequent to fusion and microinjection was negligible (87.8 +/- 0.6% of the total cell population were viable cells; n = 33) as determined by the Trypan Blue exclusion test. The delivery of intact antibodies raised against calmodulin directly into the cytoplasm of cultured chromaffin cells by erythrocyte ghost-mediated microinjection, inhibited catecholamine output in response to stimulation by either acetylcholine (10(-4) M) or a depolarizing concentration of potassium (56 mM). However, under these conditions, the chromaffin cell's ability to accumulate exogenous catecholamines through a high affinity uptake system, as well as the kinetic parameters that characterize this uptake mechanism remained unaltered. Furthermore, microinjection of preimmune immunoglobulin G did not modify either catecholamine uptake or stimulation-induced amine release from chromaffin cells. It therefore appears that calmodulin may play a role in the process of stimulus-secretion coupling in the chromaffin cell in culture while it is of little significance to the high affinity amine uptake mechanism.

Neurofilament proteins in cultured chromaffin cells

Antibodies were raised against the 200-kd, 145-kd, and 68-kd subunits of a rat neurofilament preparation. Immunoblots showed that each antibody was specific for its antigen and that it did not cross-react with any of the two other neurofilament polypeptides. Use of the three antibody preparations to stain bovine chromaffin cells in culture by the indirect immunofluorescence technique indicated that the three neurofilament polypeptides are present in chromaffin cells maintained in culture for 3 or 7 days. The three anti-neurofilament antibodies labelled the cells in a similar pattern: very thin filaments specifically localized around the nucleus were observed whereas neurites and growth cones, developed by cultured chromaffin cells, were generally not stained. Some fibroblasts were present in our cultures but they were never stained by any of the neurofilament antibodies. This indicated that the antibodies used do not react with vimentin, the major intermediate filament protein found in fibroblasts. The three neurofilament antibodies were also used to immunoprecipitate specifically three proteins of molecular weights 210 kd, 160 kd, 70 kd from solubilized extracts of cultured chromaffin cells that were radiolabelled with [35S]methionine. These proteins correspond in molecular weight to the neurofilament triplet found in bovine brain. Finally, the presence of neurofilaments in freshly isolated chromaffin cells was tested by immunoblotting using the 68-kd antibody. A 70-kd protein was specifically stained by this antibody, suggesting that neurofilaments are not only present in cultured chromaffin cells but also in the adrenal gland in vivo. It is concluded from these results that chromaffin cells contain completely assembled neurofilaments. This additional neuronal property again illustrates that chromaffin cells are closely related to neurons and therefore represent an attractive model system for the study of functional aspects of adrenergic neurons.

Adrenal chromaffin cell calmodulin: its subcellular distribution and binding to chromaffin granule membrane proteins

Bovine adrenal medullae were homogenized in the presence or in the absence of EGTA and different subcellular fractions were prepared by differential and density gradient centrifugations. In the presence of the chelating agent, 69% of the total calmodulin, measured by radioimmunoassay, was present in the cytosol; the rest was bound to different membrane-containing fractions (nuclei, microsomal, and crude granule fraction). When the chelating agent was omitted, 43% of the calmodulin was present in the cytosol, the remaining calmodulin being membrane-bound. Further resolution of the crude granule fraction by sucrose density centrifugation demonstrated that the distribution of calmodulin in the density gradient was similar to the distribution of chromaffin granules rather than to that of mitochondria, Golgi elements, and lysosomes. In this case, there was also more calmodulin bound to chromaffin granules when EGTA was omitted from the density gradient. Experiments with 125I-calmodulin indicated the presence of high-affinity binding sites (KD = 1.3 X 10(-8) M; Bmax = 30 pmol/mg protein) for calmodulin in chromaffin granule membranes. Further, photoaffinity crosslinking experiments with 125I-calmodulin followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography indicated the presence of three calmodulin-binding polypeptide complexes (84,000; 41,000; and 38,000 daltons) in chromaffin granule membranes. These polypeptides were not labelled when either Ca2+ was omitted or an excess of nonradioactive calmodulin was present in the photolysis buffer, indicating the Ca2+ dependency and the specificity of the interaction. On the basis of the results described, it is suggested that the cellular levels of Ca2+ control the cellular distribution of calmodulin and its binding to specific chromaffin granule membrane proteins. Further, it is also suggested that the interactions between calmodulin and granule proteins might play a role in stimulus-secretion coupling.

Immunofluorescent patterns of clathrin and dopamine beta-hydroxylase in chromaffin cells in culture

Bovine chromaffin cells maintained in culture for eight days were loaded with [3H]noradrenaline and then stimulated by a depolarizing concentration (56 mM) of K+. Control and stimulated cells were fixed in 3.7% formaldehyde, treated with acetone or Triton X-100, and then exposed to antibodies raised against dopamine beta-hydroxylase (a secretory granule marker) and clathrin, and purified by affinity chromatography. The cellular distribution of the correspondent antigens was investigated by indirect immunofluorescence. Cells treated with anti-dopamine beta-hydroxylase exhibited a granular pattern of fluorescence in the cytosol of the cell body, neurites, and terminal cones. Chromaffin cells exposed to anti-clathrin also showed a punctate pattern of fluorescence staining. However, in this case, the fluorescent dots were smaller than those observed with anti-dopamine beta-hydroxylase, and they were differently distributed. The speckled anti-clathrin fluorescence was preferentially condensed in the juxtanuclear region of the cell bodies, suggesting the possibility that clathrin was concentrated at the level of the Golgi apparatus. The stimulation of cultured chromaffin cells by 10 pulses of 56 mM K+ produced 91 +/- 2% (n = 5) depletion in the [3H]noradrenaline cell content and a concomitant displacement of the dopamine beta-hydroxylase fluorescence to the periphery of the cells. Four days after cell stimulation the dopamine beta-hydroxylase fluorescence was similar to that observed in control cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of isolated chromaffin cells to study basic release mechanisms

An account is given of the authors' work with isolated adrenal chromaffin cells to study the synthesis, storage and release of catecholamines and of a number of neuropeptides endogenous to the adrenal medulla. A review of other studies in the literature with the isolated chromaffin cell system is included. It is seen that the isolated chromaffin cells are a convenient in vitro system well-suited to studies of basic release mechanisms. The isolated adrenal chromaffin cells maintain high levels of catecholamines and opiates and release them by exocytosis. The cells have both nicotinic and muscarinic receptors but only the nicotinic are involved in the agonist-evoked release of catecholamines (EC50 nicotine 5 X 10(-6) M: ACh 5 X 10(-5) M). The cells can synthesize AChE and selectively release the 10S molecular form by a mechanism different from exocytosis. Substance P (SP) modulates the secretion of catecholamines and ATP evoked by ACh or nicotine but not that evoked by K+ or veratridine. SP appears to interact with the nicotinic receptor-ionophore complex to regulate Na+ entry. SP receptors on the chromaffin cells show similar structural requirements to SP receptors in other SP responsive tissues. Binding studies on isolated chromaffin cell membranes with [4-3H-Phe]SP have shown specific binding in the nM range. In addition, at high concentrations of ACh, SP protects against nicotinic receptor desensitization. Since SP is contained in the splanchnic nerve terminals that innervate the medulla, the demonstration of SP action and SP receptors on the chromaffin cells suggests a physiological role for SP in the regulation of secretion from the adrenal medulla. Somatostatin (SS) and a number of SS analogues also inhibit release, but are approximately 15-fold less potent than SP. Leu- and Met-enkephalin, which are co-stored with adrenaline in the bovine adrenal medullary cells produce a non-specific inhibition of the nicotine-evoked release of CA, but enhance the basal release of endogenous catecholamines by a mechanism that is Ca2+-dependent, stereospecific and reversible by naloxone and naltrexone. The implication of these peptide-amine interactions for physiological processes regulating homeostasis in the adrenal are discussed.

Trifluoperazine, a calmodulin inhibitor, blocks secretion in cultured chromaffin cells at a step distal from calcium entry

Trifluoperazine, a calmodulin antagonist, inhibited the secretory response of cultured bovine adrenal medullary chromaffin cells to acetylcholine (10(-4) M) or a depolarizing concentration of [K+] (56 mM KCl) in a dose-related fashion. The ID50s of this effect were 2 x 10(-7) M and 2.2 x 10(-6) M for acetylcholine and high [K+], respectively. A decrease in external [Ca2+] concentration of the incubation medium from 4.4 to 0.275 mM resulted in an increase in the percentage of inhibition produced by trifluoperazine on the acetylcholine-evoked secretory response from 20.7 to 96.5%, respectively. However, trifluoperazine inhibited the acetylcholine-evoked catecholamine output by a similar absolute magnitude for all [Ca2+] concentrations tested with the exception of 4.4 mM [Ca2+]. Trifluoperazine, unlike the [Ca2+] channel blocker Ni2+, in concentrations (10(-6)-10(-5) M) that were found to inhibit significantly [K+]-induced amine output did not modify [K+]-induced 45Ca uptake or 45Ca efflux. However, trifluoperazine at a concentration of 2.5 x 10(-5) M was found to produce a small decrease in the 45Ca efflux curve and a decrease in the [K+]-evoked 45Ca uptake of 30 +/- 14% (n = 6). In addition, 2.5 x 10(-6) M trifluoperazine, a concentration which was found to suppress high [K+]-induced amine release by 64 +/- 5%, did not inhibit the 45Ca2+-Ca2+ exchange mechanism. These results demonstrate that trifluoperazine, an antipsychotic agent with anticalmodulin activity, blocks catecholamine release from cultured chromaffin cells at a step distal from calcium entry and, consequently, suggests a role for calmodulin in the secretory process of these cells.

Glycogen metabolism in bovine adrenal medulla

Glycogen content was determined both in whole adrenal medullary tissue and in isolated adrenal chromaffin cells, in which it responds to glucose deprivation and restoration. [14C]glucose incorporation into glycogen in isolated adrenal chromaffin cells is increased by previous glucose deprivation ("fasting"). Total glycogen synthase activities are 452 +/- 66 mU/g in whole tissue and 305 +/- 108 mU/g in isolated cells. The Km of glycogen synthase for UDP-glucose is 0.67 mM with 13 mM glucose-6-phosphate and 1 mM without this effector. The in vitro inactivation process of glycogen synthase a has been found to be mainly cyclic AMP-dependent, but it also responds to Ca2+. Total glycogen phosphorylase activities are 8.69 +/- 1.26 U/g in whole tissue and 2.38 +/- 0.30 U/g in isolated cells. The requirements for interconversion in vitro of both glycogen synthase and phosphorylase suggest a system similar to that of other tissues. During incubation of isolated adrenal chromaffin cells with 5 mM-glucose, phosphorylase a activity decreases and synthase a activity increases; these changes are more marked in "fasted" cells. Glycogen content and glycogen synthase and phosphorylase activities are higher in the adrenal medulla than in the brain, suggesting a greater metabolic role of glycogen in the adrenal medulla.

Immunohistochemical and immunocytochemical localization of myosin, chromogranin A and dopamine-beta-hydroxylase in nerve cells in culture and in adrenal glands

Dopamine-beta-hydroxylase, chromogranin A and myosin were purified from bovine adrenal medulla and antibodies prepared against these proteins. Indirect immunocytochemical methods were used to localize dopamine-beta-hydroxylase, chromogranin A and myosin in bovine adrenal medulla and myosin in rat adrenal glands and cells from rat C.N.S. maintained in primary culture. Dopamine-beta-hydroxylase and chromogranin A were found in chromaffin granules, in agreement with biochemical data and, using electron microscopy, dopamine-beta-hydroxylase was found within the matrix and in the surrounding membrane of the storage granule, whereas chromogranin A was confined to the granule matrix. Myosin was localized in the vascular system irrigating adrenal glands, fibroblasts lining the vessels and chromaffin cells. In chromaffin cells, staining was found at the cell boundaries and electron microscopy showed myosin to be associated with the plasma membrane. Faint immunocytochemical staining by antimyosin antibodies was observed around certain exocytotic profiles but particular association with such structures was not demonstrable. Myosin localization was also studied in bovine adrenal cortex, where it was found in vascular channels and faintly in adrenal cortical cells, as in rat adrenal cortex and medulla, where identical patterns were obtained. In neuronal and glial cells dissociated from 13 day rat embryo cerebral hemispheres and cultured for 48 h, localization of myosin was studied using immunohistochemistry. The neuritic expansions and growth cones of neurons were fluorescent, whereas in glial cells, filamentous networks were visualized enclosing the nucleus and as long fibres traversing the entire cytoplasm.