Time course of release of catecholamine and other granular contents from perifused adrenal chromaffin cells of guinea-pig

Mice overexpressing chromogranin A display hypergranulogenic adrenal glands with attenuated ATP levels contributing to the hypertensive phenotype

OBJECTIVE

Elevated circulating chromogranin A (CHGA) is observed in human hypertension. CHGA is critical for granulogenesis and exocytosis of catecholamine stores from secretory large dense core vesicles (LDCV). This study aims to understand the morphological, molecular and phenotypic changes because of excess CHGA and the mechanistic link eventuating in hyper-adrenergic hypertension.

METHODS

Blood pressure and heart rate was monitored in mouse models expressing normal and elevated level of CHGA by telemetry. Catecholamine and oxidative stress radicals were measured. Adrenal ultrastructure, LDCV content and mitochondrial abundance were compared and respiration analyzed by Seahorse assay. Effect of CHGA dosage on adrenal ATP content, electron transport chain components and uncoupling protein 2 (UCP-2) were compared in vivo and in vitro.

RESULTS

Mice with excess-CHGA displayed hypertensive phenotype, higher heart rate and increased sympathetic tone. They had elevated plasma catecholamine and adrenal ROS levels. Excess-CHGA caused an increase in size and abundance of LDCV and adrenal mitochondria. Nonetheless, they had attenuated levels of ATP. Isolated adrenal mitochondria from mice with elevated CHGA showed higher maximal respiration rates in the presence of protonophore, which uncouples oxidative phosphorylation. Elevated CHGA resulted in overexpression of UCP2 and diminished ATP. In vitro in chromaffin cells overexpressing CHGA, concomitant increase in UCP2 protein and decreased ATP was detected.

CONCLUSION

Elevated CHGA expression resulted in underlying bioenergetic dysfunction in ATP production despite higher mitochondrial mass. The outcome was unregulated negative feedback of LDCV exocytosis and secretion, resulting in elevated levels of circulating catecholamine and consequently the hypertensive phenotype.

On-line measurement of adenosine triphosphate and catecholamine released from adrenal chromaffin cells

Adenosine triphosphate (ATP) and catecholamine (CA) released from cultured porcine adrenal chromaffin cells were continuously measured with an ATP photometer (luciferin-luciferase method) and electrochemical detector, respectively. Application of acetylcholine (ACh, 0.1 mM) or high K+ (60 mM) caused increases of ATP and CA in perfused effluent with the same time course. The peak molar ratio of CA to ATP in the effluent was about 10 for ACh and high K+ stimulation. The high-performance liquid chromatographic (HPLC) analysis of adenine nucleotides in the collected effluent revealed that the relative amounts of ATP, ADP and AMP were almost the same throughout the period of stimulation, suggesting that ATP breakdown in the effluent was constant. Changes in the peak molar ratio of CA to ATP appearing in the effluent did not occur with repetitive high K+ or sustained Ba2+ stimulation (5 mM). The similarity between the time courses of ATP and CA appearing in the effluent suggests that releasable chromaffin granules have a constant molar ratio of CA to ATP. The on-line system developed is a simple and rapid method for examining ATP and CA secretion, simultaneously.

Characteristics of 5-HT-containing chemoreceptor cells of the chicken aortic body

1. Voltage-dependent and oxygen-sensitive currents in 5-HT-containing epithelioid cells isolated from chicken thoracic aorta were examined using the whole-cell patch clamp technique. 5-HT immunoreactive cells were identified with Neutral Red. The release of 5-HT from chicken thoracic aorta in the presence of excess KCl and veratridine was also examined using HPLC. 2. At a holding potential of -70 mV with CsCl pipette solution, depolarizing steps between -30 and +60 mV produced inward currents that were blocked by tetrodotoxin (0.2 microM). In the presence of tetrodotoxin and BaCl2 (5 mM), depolarizing steps evoked slow inward currents that were sensitive to CoCl2 (2 mM). Nifedipine (1 microM) decreased the currents to 79.4 +/- 1.7 %, and omega-conotoxin GVIA (1 microM) to 20.2 +/- 3.8 %. 3. When KCl pipette solution was used, depolarizing potentials positive to -40 mV caused outward currents that were inhibited by tetraethylammonium chloride. The K+ currents evoked by depolarizing steps to +20 mV were reduced to 90.3 +/- 0.8 % by hypoxia in five out of seven cells. Two cells failed to respond to hypoxia. The K+ current response was partly decreased by Neutral Red (20 microM). 4. Excess KCl (60 mM) and veratridine (30 microM) both caused the release of 5-HT from aortic strips. 5-HT outputs induced by both stimuli were partly inhibited by nifedipine (1 microM) and by omega-conotoxin GVIA (1 microM), and were abolished by these drugs in combination and by extracellular Ca2+ removal. 5. These results suggest that epithelioid cells containing 5-HT act as chemoreceptor cells in the chicken aortic body, having voltage-dependent Na+, K+, and L- and N-type Ca2+ channels, and oxygen-sensitive K+ channels.

Modulation of calcium current by ATP in guinea-pig adrenal chromaffin cells

The effects of extracellular adenosine 5'-triphosphate (ATP) on voltage-dependent Ca2+ currents were examined using the whole-cell voltage-clamp technique in guinea-pig isolated adrenal chromaffin cells. ATP (500 microM) reversibly suppressed Ca2+ currents in the presence of 5mM Ca2+ in the extracellular solution. The inhibitory effect of ATP on Ca2+ currents tended to increase with increases in the peak amplitude of ATP-evoked current when the intracellular solution contained 0.1 or 1 mM ethylenebis(oxonitrilo)tetraacetate(EGTA). Using the intracellular solution containing 10mM EGTA, on the other hand, the inhibitory effect did not change regardless of the amplitude of current responses to ATP. In the presence of 10 mM Ba2+, ATP (100 microM) reduced Ba2+ currents in a manner similar to Ca2+ currents. This reduction was decreased by dialysis of cells with the internal solution containing guanosine 5'-O-(2-thiodiphosphate) (GDP [beta-S]; 1 mM) or guanosine 5'-O-(3-thiotriphosphate) (GTP [gamma-S]; 100 microM). A depolarizing prepulse to + 100 mV partly relieved ATP-induced reduction of Ba2+ currents. ADP, AMP and adenosine also reduced Ba2+ currents and the effect of adenosine was the most potent. Adenosine (0.5 and 1 mM) significantly inhibited adrenaline secretion induced by nicotine (50 microM). These results suggest that Ca2+ entry through ATP-activated non-selective cation channels results in the inactivation of voltage-dependent Ca2+ channels. In addition, ATP seems to modulate Ca2+ channels via the pathway related to G-protein. Adenine nucleotides and adenosine may play a role in controlling secretory activity in guinea-pig adrenal chromaffin cells.

Characteristics of ATP-induced catecholamine secretion from adrenal chromaffin cells of the guinea-pig

The effect of ATP on catecholamine secretion and intracellular Ca2+ concentration ([Ca2+]i) was examined using perfused adrenal glands and dispersed chromaffin cells of the guinea-pig. The application of ATP (2 to 10 mM) for 2 min caused a dose-dependent increase in catecholamine secretion from perfused adrenal glands. ADP, but neither AMP nor adenosine, was also effective in increasing catecholamine secretion, though its potency was much less than that of ATP. 3. The ATP-induced secretory response was observed even under Na(+)-deficient conditions, but was reversibly abolished by removal of extracellular Ca2+. 4. In dispersed chromaffin cells, ATP (0.5 mM) caused increases in catecholamine secretion and [Ca2+]i, both of which were abolished after the removal of extracellular Ca2+. 5. These results indicate that ATP released from adrenal chromaffin cells together with catecholamine may exert a positive feedback influence on the following exocytotic catecholamine secretion. This effect may be accomplished by increasing the entry of extracellular Ca2+, but not by mobilizing intracellular Ca2+ stores in adrenal chromaffin cells of the guinea-pig.

Diadenosine tetraphosphate is co-released with ATP and catecholamines from bovine adrenal medulla

Secretion of adenosine(5')tetraphospho(5')adenosine (Ap4A) and ATP from perfused bovine adrenal glands stimulated with acetylcholine or elevated potassium levels was measured and compared with that of catecholamines. We have found a close correlation between the release of Ap4A and catecholamines elicited with all the secretagogues used in the presence of either Ca2+ or Ba2+, suggesting co-release of both constituents from the chromaffin granules. By contrast, ATP secretion, as measured with luciferase, showed a significantly different time course regardless of the secretagogue used. ATP secretion consistently decreased after 1-2 min of stimulation at a time when Ap4A and catecholamine secretions were still increasing. Measures of degradation of injected [3H]ATP to the gland during stimulation showed little difference in the level of uptake or decomposition of ATP throughout the pulse. However, a reexamination of ATP secretion by monitoring its products of degradation (AMP, adenosine, and inosine) by HPLC techniques showed that Ap4A, ATP, and catecholamines are indeed secreted in parallel from the perfused adrenal gland.

Multiple forms of human dopamine beta-hydroxylase in SH-SY5Y neuroblastoma cells

Dopamine beta-hydroxylase exists as three forms in human neuroblastoma (SH-SY5Y) cells. The membrane-bound form of the hydroxylase contains three different species with apparent relative molecular weights of 73,000, 77,000, and 82,000. The intracellular soluble form of dopamine beta-hydroxylase was present as a single species with an apparent molecular weight of 73,000. Pulse-chase experiments showed that membranous dopamine beta-hydroxylase contains two subunit forms of 73,000 and 77,000 after short chase times. The soluble hydroxylase was synthesized as a single species of 73,000 at approximately the same rate as the lower molecular weight species of the membranous enzyme. A constitutively secreted third form of the enzyme with an intermediate apparent molecular weight also incorporated [35S]sulfate, whereas no significant amount of [35S]sulfate was observed in the cellular forms of the enzyme. The [35S]sulfate was incorporated on N-linked oligosaccharides. Approximately 12% of the enzyme is released constitutively within 1 h. These results demonstrate that neuronal cells have the ability to constitutively secrete a specific form of dopamine beta-hydroxylase which may contribute to the levels of this enzyme found in plasma.

Osmotic strength differentiates between two types of calcium transport pathways regulating catecholamine secretion from cultured bovine chromaffin cells

Calcium transport and catecholamine secretion was measured in cultured bovine chromaffin cells. Calcium ions which entered the cells following stimulation with either nicotine or 50 mM KCl (high potassium) triggered catecholamine release, but then inactivated the secretory process. The nicotine and the high potassium-induced calcium transport mechanisms were mechanistically distinct, but functionally dependent on each other. The specific evidence is that whereas the high potassium-induced Ca2+ influx was found to be inhibited by hyperosmotic medium, the nicotine-stimulated calcium influx was unaffected under these conditions. High potassium and nicotine-stimulated catecholamine release were also differently affected by hyperosmotic medium. While potassium-stimulated catecholamine release was profoundly inhibited by hyperosmolarity, nicotine-stimulated release was only moderately inhibited. Sequential treatments of cells with nicotine and high potassium, under isotonic physiological conditions, indicate that there is a functional, biochemical communication between the otherwise mechanistically distinct calcium channels. Calcium ions which were found to inactivate these channels may be the basis for such communication.

Kinetic characteristics of calcium-dependent, cholinergic receptor controlled ATP secretion from adrenal medullary chromaffin cells

Adrenal chromaffin cells secrete catecholamines (CA) and ATP in response to acetylcholine (ACh) and high [K+]o. The release process is relatively fast making it difficult to measure the early phase of the secretory response. Recently we were able to resolve the time course of the secretory response by measuring the release of ATP using luciferin-luciferase included in the extracellular medium. For the three secretagogues studied, ACh, nicotine and high [K+]o, the early phase of release followed a complex kinetics. Allowing for an initial delay of the secretory response, the kinetics could be described as the sum of two power exponential processes. Increasing the temperature from 23 to 37 degrees C induced a marked decrease in the two time constants needed to fit the early time course of the ATP secretion. The activation energies, estimated from Arrhenius plots, were approx. 20 and 16 kcal/mol for both phases of ATP release induced by either cholinergic agonists or high [K+]o. These results suggest that cholinergic receptor activation and membrane depolarization induce ATP (and CA) secretion through a common pathway. The initial delay in the onset of the secretory response decreased with increasing doses of secretagogue and with temperature. We propose that the delay preceding the actual onset of ATP release represents the time required for generation of intracellular second messengers. The effective concentration attained by these messengers depend apparently on both receptor occupancy by the agonist and the ensuing Ca2+ channel activation.

Sodium ions inhibit the stimulant action of caffeine on catecholamine secretion from adrenal chromaffin cells of the guinea pig

Catecholamine secretion evoked by caffeine (40 mM) was markedly enhanced by replacing NaCl in the medium with sucrose or KCl in the absence, but not in the presence, of extracellular Ca2+ and Mg2+ in both perfused adrenal glands and isolated chromaffin cells of the guinea pig. The response to caffeine declined on repetition, but was restored completely after readmission of Ca2+. These results indicate that extracellular Na+ inhibits caffeine from stimulating catecholamine secretion, which may be mediated by a release of Ca2+ from intracellular storage sites in the adrenal chromaffin cells in the presence of extracellular Ca2+ and/or Mg2+.

Real-time monitoring of the secretory function of cultured adrenal chromaffin cells

A system to discriminate the real-time dynamics of the secretory function in cultured adrenal chromaffin cells, using a cell bed perfusion technique and an amperometric detector, was established. Examination of basal conditions revealed that the electrode potential and flow rate are crucial factors for monitoring precise dynamics of the secretory process. Stimulation of the cells either with acetylcholine (ACh) or with high K+ concentration caused a transient current response. The current responses showed concentration dependence for both stimuli, and also showed a high correlation with the amount of catecholamines (CA) in the respective peak fraction of perfusate. Either prolonged cholinergic stimulation or maintained depolarization produced a transient response, which is not attributable to a depletion of releasable storage of CA as indicated by double-stimulation experiments. Stimulation with high K+ concentration evoked an additional release of CA even after the cellular response to prolonged ACh was inactivated, whereas maintained depolarization with high K+ produced both facilitatory and inhibitory effects on the cell responsiveness to ACh. Most probably the transient natures of the secretory responses to ACh and to high K+ are mediated by different mechanisms. All the results suggest that the direct monitoring is profitable for studies on the regulatory mechanisms of the secretory function.

Release of catecholamines from superfused bovine adrenal chromaffin cells cultured on microcarrier beads

A procedure is described for the establishment of stable primary cultures of bovine chromaffin cells on microcarrier beads. The cells flatten and send out processes with varicosities over a few days and maintain their catecholamine content for 2 weeks. The beads may be incorporated into a superfusion apparatus with a chamber volume of about 150 microliters, enabling the efficient perfusion of a high density of cells. The response to the introduction of nicotine and high potassium into the perfusing medium is shown to be more rapid and more transient than hitherto described, with each secretagogue producing a different degree of preferential stimulation of noradrenaline-secreting cells.

Facilitation of transmitter action on catecholamine output by cardiac glycoside in perfused adrenal gland of guinea-pig

Effects of K+ deprivation and ouabain on catecholamine secretion evoked by splanchnic nerve stimulation (5 Hz), ACh (10(-5) M) and/or excess K+ (56 mM) were studied in isolated and perfused adrenal glands of guinea-pig. Exposure to K+-free Locke solution initially reduced and later enhanced catecholamine secretion sequentially evoked by splanchnic nerve stimulation and ACh. The enhancement attained a maximum, 185% in magnitude of the corresponding control response at 35 min for splanchnic nerve stimulation and 135% at 65 min for ACh after the start of exposure to K+-free solution. Ouabain (10(-5) M) caused a larger increase in the evoked catecholamine section than K+ deprivation did. The maximum effect was obtained from 40 to 50 min after the start of exposure to ouabain in which the magnitude of responses to splanchnic nerve stimulation, excess K+ and ACh was about 500, 400 and 300% of each control response, respectively. The effect of ouabain on the evoked catecholamine secretion increased as the concentration of extracellular Na+ was increased from 25 to 154 mM, regardless of the kind of stimuli. The ouabain-induced enhancement in the evoked responses was reversibly inhibited by removing Ca2+ from, or by adding Mg2+, Co2+ or Ni2+ to the perfusion medium. The ID50 values for Mg2+ were about 9.4 and 7.3 mM and those for Co2+ were 0.8 and 0.4 mM against ouabain on the responses to ACh and excess K+, respectively. The inhibitory effect of Mg2+ and Co2+ on the ouabain action was counteracted by increasing the concentration of Ca2+ from 2.2 to 8.8 mM in the perfusion medium. These results suggest that ouabain enhances catecholamine secretion evoked by splanchnic nerve stimulation, ACh and excess K+ by increasing the rate of Ca2+ influx through the ACh receptor linked Ca2+ channel and/or voltage-dependent Ca2+ channels on adrenal chromaffin cells of guinea-pig in a Na+-dependent manner.

Adrenal medullary responses to insulin-induced hypoglycaemia in the young rat. Influence of thyroid hormones

The adrenal medulla of normal, hypothyroid and hyperthyroid young rats was stimulated by insulin-induced hypoglycaemia. In normal rats, insulin-induced adrenal epinephrine secretion increases during the first 10 days of post-natal life. Hypothyroidism retards the development of adrenal response; hyperthyroidism facilitates the development of this response. At 14 days, when insulin-induced adrenal epinephrine depletion is the same for all groups, the recovery of adrenal catecholamines stores after depletion is linear and takes less than 48 h. Recovery rate is slightly slower for hyperthyroid rats than for either hypothyroid or control rats at 14 days. Following epinephrine depletion, adrenal tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) activities are increased for a few days in the control rats, corresponding to a transsynaptic induction. Hypothyroidism impairs TH induction and completely suppresses DBH induction; hyperthyroidism impairs TH induction, but has no effect on DBH induction. These data show that the various processes related to CA synthesis, in the adrenal medulla of the developing rat, are controlled in different ways by the thyroid hormones.

The kinetics of adrenal catecholamine secretion elicited by splanchnic nerve stimulation or by Ach is consistent with non-exocytotic, multivesicular release on cation exchange basis

In eight anaesthetized cats, one dog and one pig the left adrenal was activated during a 5-15-min period by splanchnic nerve stimulation (10-30 V, 0.2-2 ms) at supramaximal frequencies (10-50 Hz) or by i.a. infusion of acetylcholine in high concentration (10(-4) M). The catecholamine (CA) release, as recorded in the adrenal venous outflow, was characterized by a very steep rise to a peak (within less than 10 s), followed by a rapid decline which after 5-10 min continued as a 'steady state' secretion, still above prestimulatory level. The initial release curve satisfied the straight line equation log B = K square root (sigma ml) + log Bmax, shown previously by us to be characteristic of the cation-induced amine release from amine-charged IRC 50 (a synthetic carboxyl cation exchanger resin) and from chromaffin granules in vitro which occurred on superfusion of these materials with isotonic NaCl solution (Uvnäs & Aborg 1984a). The initial CA-release, which depending on the intensity of the stimulus amounted to between 0.1 and approximately 5% of the adrenal CA content is suggested to reflect the rapid depletion of a CA pool for immediate release composed of granules 'lined up' for secretion adjacent to the plasma cell membrane. On depolarization of this membrane the granules are assumed to become attached to it and CA release to occur as a cation exchange, between CA+ in the granule matrix and Na+ in the plasma or possibly K+ in the cytoplasm. The transition from depletion to 'steady state' phase is assumed to reflect resynthesis or other compensatory refilling of the releasable depot evoked by its depletion. Cation exchange is suggested to be a general principle in the release of biogenic amines, including transmitter amines and other co-stored charged substances, e.g. polypeptides.