Production and release of acetylcholinesterase by a primary cell culture of bovine adrenal medullary chromaffin cells

Reduced acetylcholinesterase (AChE) activity in adrenal medulla and loss of sympathetic preganglionic neurons in TrkA-deficient, but not TrkB-deficient, mice

TrkA high-affinity receptors are essential for the normal development of sympathetic paravertebral neurons and subpopulations of sensory neurons. Paravertebral sympathetic neurons and chromaffin cells of the adrenal medulla share an ontogenetic origin, responsiveness to NGF, and expression of TrkA. Which aspects of development of the adrenal medulla might be regulated via TrkA are unknown. In the present study we demonstrate that mice deficient for TrkA, but not the neurotrophin receptor TrkB, show an early postnatal progressive reduction of acetylcholinesterase (AChE) enzymatic activity in the adrenal medulla and in preganglionic sympathetic neurons within the thoracic spinal cord, which are also significantly reduced in number. Quantitative determinations of specific AChE activity revealed a massive decrease (-62%) in the adrenal gland and a lesser, but still pronounced, reduction in the thoracic spinal cord (-40%). Other markers of the adrenal medulla and its innervation, including various neuropeptides, chromogranin B, secretogranin II, amine transporters, the catecholamine-synthesizing enzymes tyrosine hydroxylase and PNMT, synaptophysin, and L1, essentially were unchanged. Interestingly, AChE immunoreactivity appeared unaltered, too. Preganglionic sympathetic neurons, in contrast to adrenal medullary cells, do not express TrkA. They must, therefore, be affected indirectly by the TrkA knock-out, possibly via a retrograde signal from chromaffin cells. Our results suggest that signaling via TrkA, but not TrkB, may be involved in the postnatal regulation of AChE activity in the adrenal medulla and its preganglionic nerves.

Expression of dimeric and tetrameric acetylcholinesterase isoforms on the surface of cultured bovine adrenal chromaffin cells

Acetylcholinesterase is a highly polymorphic enzyme, which can be anchored to the cell surface through several different mechanisms. Dimeric (G2) acetylcholinesterase isoforms are attached by a glycosyl-phosphatidyl-inositol (GPI) linkage, whereas tetrameric (G4) forms are linked through a 20 kilodalton hydrophobic subunit. Although cells of haemopoietic origin contain large amounts of G2 GPI-linked acetylcholinesterase, most tissues express only trace amounts of this isoform. We examined the expression of acetylcholinesterase isoforms in cultured bovine adrenal medullary chromaffin cells. Two major isoforms (G2 and G4) were identified on the cell surface. The G2 isoform, which accounted for approximately half the cell-surface enzyme activity, was linked to the membrane through a GPI anchor. After treatment with diisopropylfluorophosphate to completely inhibit cellular acetylcholinesterase, the G4 isoform was found to be resynthesised and transported to the cell surface more rapidly than the G2 isoform. As the addition of GPI anchors is known to be a very rapid step, this finding suggested that the G2 and G4 isoforms might be transported to the cell surface by two different mechanisms. This conclusion was supported by results from subcellular fractionation experiments. The ratio of G4/G2 membrane-bound acetylcholinesterase varied between different subcellular fractions. The membrane-bound G2 isoform was greatly enriched in a high-speed "microsomal" fraction. G4 acetylcholinesterase is known to be actively secreted by chromaffin cells in culture. Although the G4 isoform was present on the cell surface, most of the secreted enzyme was derived from an intracellular pool. Thus, it is unlikely that the cell-surface G4 isoform contributes significantly to the pool of secreted enzyme. Instead, the expression of two different membrane-bound isoforms may provide a means by which chromaffin cells can target the enzyme to different locations on the cell surface.

Quantitation of epinephrine and norepinephrine secretion from individual adrenal medullary cells by microcolumn high-performance liquid chromatography

The cellular response of individual adrenal medullary cells to a prolonged stimulation with carbamylcholine (carbachol) was studied using microcolumn high-performance liquid chromatography (MHPLC) with electrochemical detection. Chromaffin cells will not release all of their catecholamine stores when continuously exposed to a secretagogue. The process of desensitization prevents the continued release of catecholamines after a certain percentage of chemical stores have been depleted. The percentage of a cell's chemical stores released upon stimulation was determined, and whether there is a difference in release between the cell types was examined. A single cell was exposed to a stimulation solution for 5.0 min at 25 degrees C. Approximately 80% of the solution was removed and analyzed on a microcolumn reversed-phase chromatography column. A lysing solution was immediately added to the miniaturized vial which still contained the cell, and this solution was also analyzed chromatographically. The first run was used to determine the amount of catecholamine the cell released upon stimulation. The second run determined the amount of catecholamine that remained in the cell. From these values the percentage of catecholamine released was calculated. Twenty-seven individual cells were studied by this method, and 22 could be classified as norepinephrine or epinephrine dominant. There was no statistical difference in the amount of catecholamine the norepinephrine dominant cells released (14 +/- 5%, n = 11) as compared to the epinephrine dominant cells (12 +/- 4%, n = 11).

Mouse adrenal chromaffin cells can transform to neuron-like cholinergic phenotypes after being grafted into the brain

The development of neuron-like cholinergic immunophenotypes by adrenal chromaffin cells was studied in 10-week-old mouse adrenal medullary grafts. Fragments of chromaffin tissue were implanted into mouse hippocampus, and antibodies specific for neurofilaments (NF), neuron-specific enolase (NSE), choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and phenylethanolamine-N-methyltransferase (PNMT) were applied to the grafts. Adrenal medulla grafts survived well and most of the transplanted cells were either round or polygonal. A minority of chromaffin cells elaborated an intermediate or sympathetic neuron phenotype. Chromaffin cells showed pronounced immunoreactivity for NSE in their perikarya and axon-like processes: immunoreactivity for NF was only found in a few processes. In adjacent immunohistochemically stained sections, the transplanted cells stained for ChAT and AChE. At the electron-microscope level, the immunohistochemical reactions for the two acetylcholine-related enzymes were mainly located on the endoplasmic reticulum and in cell processes. Immunoreactivity for PNMT was found to decline in transplanted chromaffin cells below that of normal adrenal medulla. These observations suggest that, in adrenal medullary grafts implanted into the hippocampus, chromaffin cells are endowed with neuron-like cholinergic immunophenotypes.

Regulation of acetylcholinesterase secretion from perfused bovine adrenal gland and isolated bovine chromaffin cells

The secretion of acetylcholinesterase (AChE) was studied in an isolated perfused bovine adrenal gland preparation and in cultured bovine adrenal medullary chromaffin cells. Electrical field stimulation (10 Hz) of splanchnic nerve terminals in the isolated perfused gland resulted in a two-fold increase in AChE secretion from the gland. Perfusion with the cholinergic receptor antagonists mecamylamine (5 microM) and atropine (1 microM) inhibited 70% of the stimulated secretion of AChE, demonstrating that most of the stimulated secretion was derived from chromaffin cells. The effect of nicotine stimulation on the secretion of AChE from isolated bovine chromaffin cells was compared with that produced by other compounds (histamine, angiotensin II) which are known to stimulate secretion of catecholamines. Incubation with nicotine (1-25 microM) stimulated the secretion of catecholamines and AChE. Histamine (1 nM-10 microM) and angiotensin II (10 pM-10 microM) did not stimulate AChE secretion. Time-course studies of AChE resynthesis after irreversible inhibition with the esterase inhibitor diisopropylfluorophosphate (DFP) demonstrated that AChE is stored within chromaffin cells for at least 11 h before being secreted. AChE secretion was inhibited within 2-3 h by 10 micrograms/ml brefeldin A (BFA), a compound known to block protein translocation from the endoplasmic reticulum (ER) to the Golgi apparatus (GA). The results suggest that AChE may reside for 8-9 h within the lumen of the ER before being actively secreted by processing through the GA.

Subcellular distribution of acetylcholinesterase forms in chromaffin cells. Do chromaffin granules contain a specific secretory acetylcholinesterase?

The presence of acetylcholinesterase (AChE) in chromaffin granules has been controversial for a long time. We therefore undertook a study of AChE molecular forms in chromaffin cells and of their distribution during subcellular fractionation. We characterized four main AChE forms, three amphiphilic forms (Ga1, Ga2 and Ga4), and one non-amphiphilic form (Gna4). Each form shows the same molecular characteristics (sedimentation, electrophoretic migration, lectin interactions) in the different subcellular fractions. All forms are glycosylated and seem to possess both N-linked and O-linked carbohydrate chains. There are differences in the structure of the glycans carried by the different forms, as indicated by their interaction with some lectins. Glycophosphatidylinositol-specific phospholipases C converted the Ga2 form, but not the other amphiphilic forms, into non-amphiphilic derivatives. The distinct patterns of AChE molecular forms observed in various subcellular compartments indicate the existence of an active sorting process. Gna4 was concentrated in fractions of high density, containing chromaffin granules. We obtained evidence for the existence of a lighter fraction also containing chromogranin A, tetrabenazine-binding sites and Gna4 AChE, which may correspond to immature, incompletely loaded granules or to partially emptied granules. The distribution of Gna4 during subcellular fractionation suggested that this form is largely, but not exclusively, contained in chromaffin granules, the membranes of which may contain low levels of the three amphiphilic forms.

Catecholamine metabolism in pheochromocytoma and normal adrenal medullae

The tissue contents of catecholamine, its precursor and its major metabolites were determined in 8 human pheochromocytomas and 26 normal adrenal glands. Pheochromocytomas contained significantly larger amounts of norepinephrine, dopamine, dihydroxyphenylalanine, tyrosine hydroxylase activity, metanephrine, normetanephrine and vanillylmandelic acid than did normal adrenal medullae. The content ratio of epinephrine/norepinephrine in normal adrenal medullae was significantly higher than that in pheochromocytomas but there were considerable individual variations in the metanephrine/normetanephrine and vanillylmandelic acid/3-methoxy-4-hydroxyphenylethylglycol ratios in pheochromocytomas. In normal adrenal medullae the tissue content of tyrosine hydroxylase activity correlated inversely with the tissue contents of epinephrine (r equals -0.78, p less than 0.001), norepinephrine (r equals -0.78, p less than 0.001) and total catecholamines (r equals -0.87, p less than 0.001), respectively but no significant relation was found between both parameters in pheochromocytomas. These results indicate the possible presence of a negative feedback mechanism of catecholamine via tyrosine hydroxylase in normal adrenal medullae but none in pheochromocytomas. In addition, the increased degradation catecholamine pathway in pheochromocytomas appears to be unstable compared to that in normal adrenal medullae.

Kinetic analysis of the triggered exocytosis/endocytosis secretory cycle in cultured bovine adrenal medullary cells

Cultured bovine adrenal medullary cells are an excellent preparation for quantitative analysis of the secretory exocytosis/endocytosis cycle. In this paper we examine the kinetics of endocytosis after stimulation of secretion. Membrane retrieval was monitored by uptake of the fluid phase marker horseradish peroxidase. Horseradish peroxidase was found to be suitable because it can be washed off completely, assayed quantitatively, and its uptake increases linearly with concentration. If this marker is present during stimulation, the rate of uptake is initially slower than catecholamine secretion but faster at a later time, suggesting that the formation of endocytotic vesicles follows exocytosis. To monitor the time-dependent concentration of secretory vesicle-plasma membrane fusion product (omega-profiles), secretion was halted at various time intervals after stimulation and the excess membrane allowed to transform into endocytotic vesicles in the presence of horseradish peroxidase. By adding horseradish peroxidase at various times after inhibition of secretion, the time course of membrane retrieval could be measured directly. All our results are consistent with a two-step kinetic model in which exocytosis and membrane retrieval are consecutive events. The estimated volumes of the compartments involved are roughly equal. The rate of endocytosis is strongly temperature-dependent but unaffected by extracellular calcium in the range of 10(-8)-2.5 X 10(-3) M, suggesting that calcium is not required at the site of endocytotic membrane fusion. Membrane retrieval is also unaffected by Lanthanum (1 mM) but is slowed by hypertonic media.

Selective induction of tyrosine hydroxylase by cell-cell contact in bovine adrenal chromaffin cells is mimicked by plasma membranes

As a first step towards the identification and purification of the molecule(s) that are involved in cell contact-mediated tyrosine hydroxylase (TH) induction in cultures of bovine adrenal chromaffin cells, we have prepared plasma membranes (PM) from bovine adrenal medulla and tested their ability to mimick cell contact-mediated TH induction in low density chromaffin cultures. PM indeed induced TH in a manner similar to that observed in high density cultures. The maximal TH induction reached by PM corresponded to 69% of that of high density cultures, and half-maximal TH induction was obtained with 12 micrograms of PM per ml of medium. The induction of TH by PM was blocked by alpha-amanitin as observed in high density cultures. Since acetylcholinesterase was neither induced in high density nor in PM-treated low density cultures, an induction of TH as a result of a general increase in protein synthesis was excluded. The cell contact molecule(s) appear to be intrinsic membrane proteins. They were not removed by high or low salt extraction, but solubilized by 50 mM octylglucoside. They were resistant to 0.1% trypsin and heat denaturation but inactivated by 0.01% chymotrypsin. PM isolated from the adrenal cortex, kidney, and liver also induced TH in low density chromaffin cell cultures, although to a smaller extent than PM of the adrenal medulla. In contrast, muscle and erythrocyte PM were inactive. This shows that the cell contact molecule(s) are not restricted to the adrenal medulla, but are also present in some other but not all tissues.

Morphologic and biochemical variability of tissue and cultured cells from human pheochromocytoma

Primary cell cultures from 18 human pheochromocytomas were maintained in culture for 10 to 12 days and characterized. The cell yields ranged from 1.0 to 60.1 X 10(6) cells/g wet weight of tissue. Cell size, as determined by histofluorescent microscopy, varied as much as seven-fold among cells derived from a given tumor and ten-fold between cells from all tumors. Cell catecholamine content, norepinephrine (NE) plus epinephrine, ranged from 0.4 to 89.5 nmol/10(6) cells at day 5 in culture and did not correlate with catecholamine content of the tissue from which the cells were obtained. Cell catecholamine content decreased with time in culture, but this decrease could not be related to a change in cell viability, the type of media used, an inability to convert dopamine to NE, or an alteration in the uptake of 3H-NE. Cellular uptake of 1.0 microM 3H-NE varied as much as 230-fold between all cell dispersions. The basal and acetylcholine stimulated release of both preloaded 3H-NE and the endogenous catecholamines was quite variable. There was no correlation between the release rate, either basal or stimulated, of preloaded 3H-NE and the endogenous catecholamines. This study represents the largest existing data base on culturing cells from these tumors and describes many of the morphologic and biochemical characteristics of this cell system.

H1-histaminergic activation stimulates inositol-1-phosphate accumulation in chromaffin cells

Adrenal medullary chromaffin cells maintained in vitro were prelabeled with [3H]inositol and the accumulation of [3H]inositol-1-phosphate, was determined following stimulation with a variety of pharmacological agents. Carbachol, bradykinin, and histamine produced significantly greater accumulation of [3H] inositol-1-phosphate over basal levels, with histamine producing the greatest effect. H1-histamine receptor antagonists, mepyramine, pyrilamine, tripelennamine and clemastine were all able to reduce or completely block the histamine response. The two specific H2-histamine receptor antagonists, cimetidine and ranitidine, had no effect on this response. Histamine dose-response characteristics in the presence of mepyramine and clemastine suggest the H1 antagonism to be competitive in nature.

Effects of opioid peptides containing the sequence of Met5-enkephalin or Leu5-enkephalin on nicotine-induced secretion from bovine adrenal chromaffin cells

Eighteen endogenous opioid peptides, all containing the sequence of either Met5- or Leu5-enkephalin, were tested for their ability to modify nicotine-induced secretion from bovine adrenal chromaffin cells. ATP released from suspensions of freshly isolated cells was measured with the luciferin-luciferase bioluminescence method as an index of secretion. None of the peptides affected 5 microM nicotine-induced ATP release at 10 nM. Three peptides inhibited secretion at 5 microM: dynorphin1-13, dynorphin1-9, and rimorphin inhibited by 65%, 37%, and 29% respectively. Use of peptidase inhibitors (bestatin, thiorphan, bacitracin, or 1,10-phenanthroline) did not result in any of the other peptides showing potent actions on the nicotinic response, although bestatin and thiorphan did enhance the inhibitory actions of dynorphin1-13 and dynorphin1-9 by 20-30%. Nicotine-induced secretion of endogenous catecholamines from bovine chromaffin cells cultured for 3 days was also studied to assess any selective actions of the peptides on adrenaline or noradrenaline cell types. Dynorphin1-13 was 1,000-fold more potent than Leu5-enkephalin at inhibiting endogenous catecholamine secretion. Dynorphin1-13 was slightly more potent at inhibiting noradrenaline release than adrenaline release whereas Leu5-enkephalin showed the opposite selectivity. The structure-activity relationships of opioid peptide actions on the chromaffin cell nicotinic response are discussed in relation to the properties of the adrenal opioid binding sites.

The release of acetylcholine and of catecholamine from the cat's adrenal gland

The cat's adrenal gland was perfused in situ with Krebs solution containing eserine; the amount of acetylcholine and of catecholamine released was measured. Splanchnic nerve stimulation (5 Hz for 2 min) increased the release of acetylcholine and catecholamine; the molar ratio of evoked release of catecholamine to acetylcholine was 122 +/- 8. It is suggested that this amplification is achieved because a chromaffin cell granule contains more mediator than does the acetylcholine quantum that releases it. The release per impulse of catecholamine during splanchnic nerve stimulation at 30 Hz was less than that released by stimulation at 1 or 5 Hz. This depression is attributed to a presynaptic failure, because the release of acetylcholine was similarly frequency dependent. The release of catecholamine was linearly related to the release of acetylcholine over the range tested, indicating that the input-output relationship at the splanchnic-adrenal medullary junction is linear. During continuous stimulation of the splanchnic nerve (5 Hz), catecholamine release declined to a level that was 32 +/- 2% of the initial output. This fatigue is attributed primarily to a postsynaptic depression, because the release of acetylcholine was maintained at 71 +/- 6% of its initial level. The presence of eserine in the perfusate was necessary for the release of acetylcholine to be detected, but in the presence of eserine catecholamine release was 90 +/- 10% that in the drug's absence. It is concluded that released acetylcholine is hydrolysed at some distance from its site of release and action. Glands perfused with raised K+ released acetylcholine and catecholamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of chromaffin secretory vesicles, acetylcholinesterase, and lysosomal enzymes in sucrose and Percoll gradients

Crude chromaffin secretory vesicles, obtained by differential centrifugation, were further purified on isotonic (Percoll) gradients. The chromaffin vesicle fractions recovered from the gradients contain acetylcholinesterase as well as lysosomal enzymes. With the aid of a subsequent sucrose gradient lysosomal enzymes could be removed from chromaffin vesicle fractions, but not acetylcholinesterase. This suggests that lysosomal enzymes do not pass through the chromaffin vesicles during the biogenesis of lysosomes but acetylcholinesterase does.

Parallel but separate release of catecholamines and acetylcholinesterase from stimulated adrenal chromaffin cells in culture

A pharmacological study was made of the effects of veratridine and lasalocid on the release of catecholamines, acetylcholinesterase (AChE) and dopamine-beta-hydroxylase (DBH) from cultures of isolated bovine adrenal chromaffin cells. Exposure of the cultures to veratridine resulted in concomitant release of catecholamines and AChE into the external medium in a dose-dependent and Ca2+-dependent manner. A Ca2+ ionophore, lasalocid, also produced a dose-dependent and parallel release of both catecholamines and AChE. The release of the two components was accompanied by release of DBH. The present results provide pharmacological evidence for a parallel release of catecholamines, AChE, and DBH from cultured adrenal chromaffin cells, and the stoichiometry of the release evoked by different secretagogues suggests that AChE and catecholamines are released from different cellular compartments.

Desensitization to nicotinic cholinergic agonists and K+, agents that stimulate catecholamine secretion, in isolated adrenal chromaffin cells

Desensitization of catecholamine (CA) release from cultured bovine adrenal chromaffin cells was studied to characterize the phenomenon of desensitization and to attempt an elucidation of the mechanism(s) involved in this phenomenon at the level of the isolated chromaffin cell. Prior exposure of chromaffin cells to nicotinic cholinergic agonists [acetylcholine (ACh) or nicotine] caused a subsequent depression or desensitization of CA release during restimulation of the cells with the same agonists. Rates of development of and recovery from nicotinic desensitization were in the minute time range and the magnitude of nicotinic desensitization of CA release was greater at 37 degrees C than at 23 degrees C. ACh- (or nicotine)-induced desensitization was shown to be the result of two processes: (1) a Ca2+-dependent component of desensitization, possibly due to a depletion of intracellular CA stores and (2) a Ca2+-independent, depletion-independent component of desensitization. Prior exposure of cultured chromaffin cells to an elevated concentration of K+ also resulted in desensitization of K+-induced CA release in these cells. K+-induced desensitization was completely Ca2+-dependent and was shown to be the result, at least in part, of a mechanism that is independent of depletion of CA stores.

Acetylcholinesterase activity of adrenal chromaffin vesicles

Biochemical studies have given conflicting interpretations as to the localization of acetylcholinesterase within adrenal chromaffin cells. Previous histochemical studies found no reaction product on the chromaffin vesicles, although some biochemical studies suggest that a form of the enzyme is present. Sensitive histochemical procedures, with the appropriate controls, suggest a small amount of acetylcholinesterase is associated with chromaffin vesicles.

Block by phencyclidine of acetylcholine and barium induced adrenal catecholamine secretion

Activation of the sympathetic system by phencyclidine (PCP) should result in catecholamine release from the adrenals. However, adrenalectomy does not reduce PCP-induced hypertension. In an attempt to rectify this inconsistency, the direct effects of PCP on the bovine adrenal medulla were examined. At (3 X 10(-6) M), PCP reduced the acetylcholine-(ACh)-induced catecholamine release by 50%. Surprisingly, barium-induced secretion of catecholamines was also reduced by PCP. ACh-induced catecholamine release was not altered by 10(-3)M 4-aminopyridine (4 AP), the potassium channel blocker. Thus, calcium antagonist actions of PCP and consequent block of catecholamine secretion from adrenal medulla may explain the lack of effect of adrenalectomy on PCP-induced hypertension. Possible contributions of calcium and/or potassium channel blockade to other manifestations of PCP overdosage are discussed.

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.

Characterization of substance P and somatostatin receptors on adrenal chromaffin cells using structural analogues

Substance P (SP) and somatostatin (SRIF) are known to inhibit the nicotine-induced release of catecholamines (CAs) from isolated adrenal chromaffin cells in culture22,24. In order to characterize the receptors mediating this action, we have tested several SP and SRIF analogues for their effects on release of [3H]L-norepinephrine ([3H]NE) from chromaffin cell cultures. SP-free acid and a series of 11 SP analogues, in which each amino acid of SP is replaced in turn by L-alanine, all inhibited the nicotine-induced release of [3H]NE from these cultures. The rank order of potency of the analogues for this action was similar to their reported order of potency in other SP-responsive tissues. The least potent were SP-free acid, [Ala7]-SP, [Ala10]-SP, [Ala8]-SP and [Ala11]-SP, while the potencies of the Ala 1 to 6 analogues and [Ala9]-SP were closer to that of SP. [Leu7]- and [Leu7,8]-SP had potencies similar to that of SP. SP itself had no effect on basal [3H]NE release and only the highest concentrations of some of the analogues tested had an effect (enhancement) on basal [3H]NE release. The results suggest that adrenal chromaffin cells possess a specific SP receptor mediating inhibition of agonist-induced CA release and that the binding site of this receptor shares similar structural requirements with the binding site of the SP receptor on other tissues. Several SRIF analogues, which have been previously shown to be more potent than native SRIF at selective SRIF receptors2,3,31, 35, were compared to SRIF for effects on [3H]NE release from chromaffin cell cultures. These analogues were found to be active but less potent than SRIF in inhibiting nicotine-induced [3H]NE release from these cultures, suggesting that the site mediating this action differs in its structural requirements from the SRIF receptor found in some other tissues.

Evidence against a generalized membrane defect in dystrophic mice platelets

The response of the membrane-bound enzyme AChE to changes in temperatures was investigated to test the applicability of the "generalized membrane defect" hypothesis proposed for human myotonic and Duchenne muscular dystrophies to the two forms of muscular dystrophy expressed in mice. For intact platelets from homozygous normal and dystrophic mice of both strains, a break (Tc) occurred in the Arrhenius plot of AChE activity at approximately 22 C. Solubilization of membrane-bound AChE by Triton X-100 produced a nonlinear Arrhenius plot over the temperature range (7.7 C to 37 C) in normal and dystrophic mice of both strains. However, in the presence of phospholipase A2 + C and Triton X-100, a linear Arrhenius plot was produced indicating that the membrane-bound enzyme is normally modulated by a bulk lipid domain as well as by a tightly bound (immobilized) phospholipid domain. The temperature response of platelet AChE from normal and dystrophic mice of both strains was not significantly different. These results showing normal temperature kinetics of AChE do not lend support to the theory of a membrane defect in the platelets of dystrophic mice.

Evidence that inhibition of nicotine-mediated catecholamine secretion from adrenal chromaffin cells by enkephalin, beta-endorphin, dynorphin (1-13), and opiates is not mediated via specific opiate receptors

The opioid peptides Met- and Leu-enkephalin, dynorphin (1-13), and beta-endorphin and the narcotic analgesics, morphine, levorphanol, and dextrorphan all produced a dose-dependent inhibition of nicotine (5 x 10(-6) M)-mediated release of [3H]norepinephrine ([3H]NE) from bovine adrenal chromaffin cells in culture. None of these agents affected [3H]NE release induced by high K+ (56 mM). Although the above results suggest that the opioid peptides and narcotic analgesics inhibit catecholamine release from adrenal chromaffin cells in culture, we suggest that these effects are not mediated by specific opiate binding sites, since (1) the inhibition was only produced with high concentrations of the agents--the threshold concentrations were 10(-7) to 10(-5)M and higher; (2) the inhibition produced by the narcotic analgesics did not display stereospecificity, because the d-isomer, dextrorphan, was slightly more active than the l-isomer, levorphanol; (3) the narcotic antagonists naloxone, naltrexone, and levallorphan did not reverse the inhibition produced by either the narcotic analgesics (e.g., morphine) or the opioid peptides (e.g., dynorphin). These three antagonists themselves inhibited the nicotine-mediated release of [3H]NE from the adrenal chromaffin cells in culture. Finally (4), the I2-Tyr1 substituted analogues of beta-endorphin and dynorphin that are biologically less active than the parent compounds produced an inhibition of the nicotine-mediated [3H]NE release similar to that of their parent compounds. These results do not support the idea that high-affinity stereospecific opiate binding sites are involved in the inhibitory modulation of nicotinic evoked catecholamine release from bovine adrenal chromaffin cells in culture.

Effects of pro-opiomelanocortin fragments on release of catecholamines from adrenal chromaffin cells

The effects of pro-opiomelanocortin (POMC) peptide fragments on the basal and agonist-induced release of catecholamines (CAs) from monolayer cultures of purified bovine adrenal chromaffin cells were tested. None of the 5 peptides tested, i.e. beta-MSH, ACTH1-39, gamma-MSH1-13, gamma 3-MSH and N-terminal POMC fragment, had any effect on basal CA release. However, beta-MSH (10(-5) M), gamma-MSH1-13 (10(-6)-10(-5) M), gamma 3-MSH (10(-5) M) and N-terminal POMC fragment (10(-5) M) inhibited the nicotine-induced release of CAs from the chromaffin cells. The possible physiological significance of this inhibitory neuromodulation is discussed.