Arachidonic acid affects membrane ionic conductances of GH3 pituitary cells

1989 ◽  
Vol 257 (2) ◽  
pp. E203-E211 ◽  
Author(s):  
P. Vacher ◽  
J. McKenzie ◽  
B. Dufy
Keyword(s):  
Arachidonic Acid ◽  
Intracellular Calcium ◽  
Voltage Clamp ◽  
Calcium Concentration ◽  
Potassium Conductance ◽  
Free Calcium ◽  
Pituitary Cells ◽  
Prolactin Release ◽  
Ionic Conductances ◽  
Voltage Dependent

Arachidonic acid (AA) stimulates prolactin release from pituitary cells, by mechanisms not yet understood. In this work, we analyzed the effects of AA on membrane ionic conductances in a clonal line of anterior pituitary cells (GH3/B6), finding time- and dose-dependent effects of AA on their membrane ionic conductances. The predominant response at concentrations between 100 nM and 10 microM was a prolongation of the action potential (AP) and an increase in the transient after-hyperpolarization potential. Voltage clamp studies showed that this was associated with a decrease in a voltage-dependent potassium current and an increase in a voltage-dependent calcium current. In some cells (30%) the effect of AP duration was less important, but spike firing was enhanced. For the highest concentrations used (1 and 10 microM) the effects described above were preceded by hyperpolarization of the cell membrane; in voltage clamp it was shown that this hyperpolarization resulted from the activation of a calcium-dependent potassium conductance suspected to be due to the release of intracellular calcium. The calcium store affected by AA was, at least in part, insensitive to vanadate and heparin. These data suggest that AA may enhance intracellular calcium concentration by increasing calcium entry during each voltage-dependent calcium AP, by increasing the spike frequency, or by releasing calcium from an intracellular compartment. The resulting rise in cytosolic free calcium concentration may be a key link in the process by which AA stimulates prolactin release in GH3/B6 pituitary cells.

Control of secretion in anterior pituitary cells--linking ion channels, messengers and exocytosis

1988 ◽  
Vol 139 (1) ◽  
pp. 287-316
Author(s):  
W. T. Mason ◽  
S. R. Rawlings ◽  
P. Cobbett ◽  
S. K. Sikdar ◽  
R. Zorec ◽  
...  
Keyword(s):  
Ion Channels ◽  
Intracellular Calcium ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
Cell Types ◽  
Pituitary Cell ◽  
Pituitary Cells ◽  
Calcium Activity ◽  
Anterior Pituitary Cells ◽  
Voltage Dependent

Normal anterior pituitary cells, in their diversity and heterogeneity, provide a rich source of models for secretory function. However, until recently they have largely been neglected in favour of neoplastic, clonal tumour cell lines of pituitary origin, which have enabled a number of studies on supposedly homogeneous cell types. Because many of these lines appear to lack key peptide and neurotransmitter receptors, as well as being degranulated with accompanying abnormal levels of secretion, we have developed a range of normal primary anterior pituitary cell cultures using dispersion and enrichment techniques. By studying lactotrophs, somatotrophs and gonadotrophs we have revealed a number of possible transduction mechanisms by which receptors for hypothalamic peptides and neurotransmitters may control secretion. In particular, the transduction events controlling secretion from pituitary cells may differ fundamentally from those found in other cell types. Patch-clamp recordings in these various pituitary cell preparations have revealed substantial populations of voltage-dependent Na+, Ca2+ and K+ channels which may support action potentials in these cells. Although activation of these channels may gate Ca2+ entry to the cells under some conditions, our evidence taken with that of other laboratories suggests that peptide-receptor interactions leading to hormone secretion occur independently of significant membrane depolarization. Rather, secretion of hormone and rises in intracellular calcium measured with new probes for intracellular calcium activity, can occur in response to hypothalamic peptide activation in the absence of substantial changes in membrane potential. These changes in intracellular calcium activity almost certainly depend on both intracellular and extracellular calcium sources. In addition, strong evidence of a role for multiple intracellular receptors and modulators in the secretory event suggests we should consider the plasma membrane channels important for regulation of hormone secretion to be predominantly agonist-activated, rather than of the more conventional voltage-dependent type. Likewise, evidence from new methods for recording single ion channels suggests the existence of intracellular sites for channel modulation, implying they too may play an important role in secretory regulation. We shall consider new data and new technology which we hope will provide key answers to the many intriguing questions surrounding the control of pituitary hormone secretion. We shall highlight our work with recordings of single ion channels activated by peptides, and recent experiments using imaging of intracellular ionized free calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypotonic stress-induced dual Ca2+ responses in bovine aortic endothelial cells

2000 ◽  
Vol 279 (2) ◽  
pp. H630-H638 ◽  
Author(s):  
Masahiro Oike ◽  
Chiwaka Kimura ◽  
Tetsuya Koyama ◽  
Miyuki Yoshikawa ◽  
Yushi Ito
Keyword(s):  
Endothelial Cells ◽  
Arachidonic Acid ◽  
Receptor Antagonist ◽  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Luciferase Assay ◽  
Aortic Endothelial Cells ◽  
Hypotonic Stress ◽  
Bovine Aortic Endothelial Cells ◽  
Aortic Endothelial

We have investigated the effects of hypotonic stress on intracellular calcium concentration ([Ca2+]i) in bovine aortic endothelial cells. Reducing extracellular osmolarity by 5% to 40% elicited a steep Ca2+ transient both in normal Krebs and Ca2+-free solutions. The hypotonic stress-induced Ca2+ transient was inhibited by phospholipase C inhibitors (neomycin and U-73122), a P2-receptor antagonist (suramin), and an ATP-hydrolyzing enzyme (apyrase), suggesting that the hypotonic stress-induced Ca2+ transient is mediated by ATP. A luciferin-luciferase assay confirmed that 40% hypotonic stress released 91.0 amol/cell of ATP in 10 min. When the hypotonic stress-induced fast Ca2+ transient was inhibited by neomycin, suramin, or apyrase, a gradual [Ca2+]i increase was observed instead. This hypotonic stress-induced gradual [Ca2+]iincrease was inhibited by a phospholipase A2 inhibitor, 4-bromophenacyl bromide. Furthermore, exogenously applied arachidonic acid induced a gradual [Ca2+]i increase with an ED50 of 13.3 μM. These observations indicate that hypotonic stress induces a dual Ca2+ response in bovine aortic endothelial cells, i.e., an ATP-mediated fast Ca2+transient and an arachidonic acid-mediated gradual Ca2+increase, the former being the predominant response in normal conditions.

Volume regulation and intracellular calcium in the rabbit proximal convoluted tubule

1991 ◽  
Vol 260 (6) ◽  
pp. F861-F867 ◽  
Author(s):  
J. S. Beck ◽  
S. Breton ◽  
R. Laprade ◽  
G. Giebisch
Keyword(s):  
Intracellular Calcium ◽  
Cell Volume ◽  
Sodium Transport ◽  
Calcium Concentration ◽  
Basolateral Membrane ◽  
Potassium Conductance ◽  
Proximal Convoluted Tubule ◽  
Intracellular Calcium Concentration ◽  
Cell Swelling ◽  
Sustained Increase

The hypothesis that an increase of calcium leads to activation of calcium-activated ionic conductances during cell swelling was examined in the isolated perfused proximal convoluted tubule of the rabbit. Reduction of bath and luminal osmolality by 90 mosmol/kgH2O caused the cells to swell by 23.6 +/- 1.5% (n = 5) and intracellular calcium to rise from 227 +/- 35 to 347 +/- 60 nM (n = 6). Both these increases were transient, with volume decreasing to 5.5 +/- 1.2% above control and intracellular calcium concentration decreasing to 272 +/- 46 nM after 5-9 min. The addition of glucose and alanine to the tubule lumen to increase transcellular sodium transport caused a sustained increase in cell volume of 15.6 +/- 3.4% (n = 4). In parallel experiments, no significant increase in intracellular calcium concentration was observed. Addition of 1 microM of the calcium ionophore, ionomycin, reversibly increased intracellular calcium by 224 +/- 60 nM from a control value of 301 +/- 29 nM (n = 7) and reversibly depolarized the basolateral membrane by 3.6 +/- 0.9 mV (n = 5). However, there was no initial increase in the apparent transference number for potassium or chloride and no significant change in cell volume. We conclude from these observations that the sustained increase in basolateral potassium conductance observed when cells are swollen by hypotonicity or increased sodium transport (J. S. Beck and D. J. Potts. J. Physiol. Lond. 425: 369-378, 1990) is not due to a calcium-activated potassium conductance.

GRF elevates cytosolic free calcium concentration in rat anterior pituitary cells

1987 ◽  
Vol 253 (5) ◽  
pp. E591-E594
Author(s):  
C. Schofl ◽  
J. Sandow ◽  
W. Knepel
Keyword(s):  
Growth Hormone ◽  
Anterior Pituitary ◽  
Calcium Concentration ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Free Calcium ◽  
Pituitary Cells ◽  
Maximal Increase ◽  
Anterior Pituitary Cells ◽  
Free Calcium Concentration

The effect of human growth hormone-releasing factor (GRF) on intracellular free calcium concentration ([Ca2+]i) was examined in rat anterior pituitary cells. The [Ca2+]i was monitored directly by means of the intracellularly trapped fluorescent indicator, fura-2. GRF rapidly elevated [Ca2+]i, reaching a new plateau within approximately 30 s. The half-maximally effective concentration of GRF was approximately 130 pM. GRF produced a maximal increase in [Ca2+]i by approximately 120 nM. The GRF (2 nM)-induced elevation of [Ca2+]i was abolished by removal of extracellular calcium (Ca2+ omitted, 2 mM EGTA). The GRF (2 nM)-caused rise in [Ca2+]i was largely reduced in the presence of the calcium channel blockers Mg2+ (31.2 mM) or nifedipine (1 microM). An increase in [Ca2+]i by approximately 60 nM was elicited by the addition of prostaglandin E2 (1 microM), which can stimulate growth hormone secretion independent of GRF receptors. These data indicate that GRF elevates the [Ca2+]i, possibly in somatotrophs; this GRF-induced increase in [Ca2+]i may depend on an influx of extracellular Ca2+, largely through Mg2+- and nifedipine-sensitive calcium channels.

Serotonin and forskolin increase an inwardly rectifying potassium conductance in cultured identified Aplysia neurons

1987 ◽  
Vol 58 (5) ◽  
pp. 909-921 ◽  
Author(s):  
D. P. Lotshaw ◽  
I. B. Levitan
Keyword(s):  
Voltage Clamp ◽  
Potassium Conductance ◽  
Phosphodiesterase Inhibitor ◽  
Identified Neurons ◽  
Inward Rectification ◽  
Current Response ◽  
Aplysia Neurons ◽  
Voltage Dependent ◽  
K Concentration ◽  
Inwardly Rectifying

1. The effect of serotonin (5-HT) and forskolin on an inwardly rectifying K+ conductance (IKR) was studied using voltage-clamp techniques in several identified Aplysia neurons isolated and maintained in primary cell culture. 2. Inward rectification was observed in the current-voltage relationship of the identified neurons R15, R2, B1, and B2 and was predominately due to IKR, as demonstrated by the dependence of inward rectification on the extracellular K+ concentration, instantaneous kinetics of the membrane current response to hyperpolarizing voltage clamp pulses, and voltage-dependent Ba2+ block of the inwardly rectifying current. 3. 5-HT increased IKR conductance between 100 and 400% in the identified neuron R15 in culture and increased IKR conductance approximately 50% in the identified neurons B1, B2, and R2 in culture. The adenylate cyclase activator, forskolin, plus a phosphodiesterase inhibitor, Ro 20-1724, also increased IKR conductance in these neurons. 4. 5-HT and forskolin modulated other ion conductances as well in all of these cultured neurons.

The development of voltege-dependent ionic conductances In murine spinal cord neurones in culture

1988 ◽  
Vol 66 (10) ◽  
pp. 1328-1336 ◽  
Author(s):  
C. Krieger ◽  
T. A. Sears
Keyword(s):  
Spinal Cord ◽  
Sodium Current ◽  
Potassium Conductance ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Calcium Dependent ◽  
Ionic Conductances ◽  
Voltage Dependent

The development of voltage-dependent ionic conductances of foetal mouse spinal cord neurones was examined using the whole-cell patch-clamp technique on neurones cultured from embryos aged 10–12 days (E10–E12) which were studied between the first day in vitro (V1) to V10. A delayed rectifier potassium conductance (IK) and a leak conductance were observed in neurones of E10.V1, E11, V1, and E12, V1 as well as in neurones cultured for longer periods. A rapidly activating and inactivating potassium conductance (IA) was seen in neurones from E11, V2 and E12, V1 and at longer times in vitro. A tetrodotoxin (TTX) sensitive sodium-dependent inward current was observed in neurones of E11 and E12 from V1 onwards. Calcium-dependent conductances were not detectable in these neurones unless the external calcium concentration was raised 10- to 20-foid and potassium conductances were blocked. Under these conditions calcium currents could be observed as early as E11, V3 and E12, V2 and at subsequent times in vitro. The pattern of development of voltage-dependent ionic conductances in murine spinal neurones is such that initially leak and potassium currents are present followed by sodium current and subsequently calcium current.

Elevation of intracellular calcium reduces voltage-dependent potassium conductance in human T cells

Nature ◽  
1986 ◽  
Vol 319 (6056) ◽  
pp. 776-778 ◽  
Author(s):  
P. Bregestovski ◽  
A. Redkozubov ◽  
A. Alexeev
Keyword(s):  
T Cells ◽  
Intracellular Calcium ◽  
Potassium Conductance ◽  
Human T Cells ◽  
Voltage Dependent

Activity-induced elevations of intracellular calcium concentration in pyramidal and nonpyramidal cells of the CA3 region of rat hippocampal slice cultures

1992 ◽  
Vol 68 (3) ◽  
pp. 961-963 ◽  
Author(s):  
T. Knopfel ◽  
B. H. Gahwiler
Keyword(s):  
Intracellular Calcium ◽  
Time Course ◽  
Calcium Concentration ◽  
Potassium Conductance ◽  
Pyramidal Cells ◽  
Calcium Transients ◽  
Intracellular Calcium Concentration ◽  
Calcium Signal ◽  
Cell Somata ◽  
Ca3 Region

1. Depolarization-induced elevations of intracellular calcium concentration ([Ca2+]i) were examined in slice-cultured hippocampal pyramidal and nonpyramidal cells of the CA3 region by combined intracellular and multisite fura-2 recording techniques. 2. In pyramidal cells, spiking activity induced by depolarizing current pulses (200–800 ms) induced transient elevations of somatic as well as of proximal dendritic [Ca2+]i. The calcium signals from the proximal dendrites were larger in amplitude and decayed much faster than those from the soma. Depolarization of presumed interneurons induced comparable somatic and dendritic calcium transients, which decayed faster than those observed in pyramidal cell somata. 3. The calcium transients of pyramidal cells, but not those of nonpyramidal cells, were associated with a slow afterhyperpolarization (sAHP), whose time course was correlated with that of the somatic calcium signal. We conclude that the lack of a sAHP in non-pyramidal cells cannot be explained by the absence of an efficient rise in [Ca2+]i but rather by the absence of the potassium conductance underlying the sAHP in pyramidal cells.

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