Norepinephrine-stimulated vascular prostacyclin synthesis. Receptor-dependent calcium channels control prostaglandin synthesis

1984 ◽  
Vol 62 (12) ◽  
pp. 1341-1347 ◽  
Author(s):  
Duncan Stewart ◽  
Elaine Pountney ◽  
David Fitchett
Keyword(s):  
Contractile Response ◽  
Fold Increase ◽  
Maximal Stimulation ◽  
Norepinephrine Concentration ◽  
Adrenergic Antagonist ◽  
Channel Blocking ◽  
Intracellular Ca ◽  
Prostaglandin F ◽  
Wet Weight ◽  
Prostacyclin Synthesis

Norepinephrine-stimulated prostacyclin synthesis was studied in rat aortic rings by measuring 6-keto-prostaglandin F1α (6-keto-PGF1α) by radioimmunoassay. Norepinephrine (10−6 M) results in a 10- to 20-fold increase in 6-keto-PGF1α synthesis by rat aortic rings (54 ± 11 to 437 ± 260 pg∙mg wet weight−1∙20 min−1). The maximal stimulation of 6-keto-PGF1α synthesis was observed with a norepinephrine concentration of 10−5 M at a mean effective concentration (EC50) of 9.5 ± 3.2 × 10−7 M which is similar to the contractile response (Emax = 10−5 M, EC50 = 6.5 ± 1.8 × 10−7 M). Potassium chloride (30 mM), although causing a similar maximal contractile response as 10−6 M norepinephrine, did not increase 6-keto-PGF1α synthesis. Norepinephrine-stimulated 6-keto-PGF1α synthesis was dependent upon extracellular calcium. Norepinephrine stimulation in Ca2+-free medium did not lead to a significant increase in 6-keto-PGF1α synthesis. However, on the introduction of Ca2+, 6-keto-PGF1α synthesis was restored to its initial level. Phentolamine (10−6 M) (an α-adrenergic antagonist) and trifluroperazine (2.5 × 10−4 M) (a calmodulin inhibitor) completely inhibited norepinephrine-stimulated 6-keto-PGF1α synthesis, whereas verapamil 3 × 10−6 M (a calcium channel blocking drug) only partially inhibited synthesis (control, 74 ± 12; norepinephrine, 437 ± 260; norepinephrine + verapamil, 123 ± 8 pg∙mg wet weight−1∙20 min−1). Norepinephrine-stimulated prostacyclin synthesis is probably α-receptor mediated and appears to depend upon the opening of receptor-operated Ca2+ channels. The operation of potential-dependent Ca2+ channels (by 30 mM KCl) in contrast, although known to be associated with an increase of intracellular Ca2+, does not stimulate PG synthesis.

scholarly journals Vasoactive Effects of Acute Ergot Exposure in Sheep

Toxins ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 291
Author(s):  
Rossalin Yonpiam ◽  
Jair Gobbet ◽  
Ashok Jadhav ◽  
Kaushik Desai ◽  
Barry Blakley ◽  
...  
Keyword(s):  
Single Dose ◽  
Chronic Exposure ◽  
Contractile Response ◽  
Ergot Alkaloids ◽  
Acute Exposure ◽  
Control Group ◽  
Vascular Effects ◽  
Adrenergic Antagonist ◽  
Vascular Sensitivity ◽  
Dose Dependent

Ergotism is a common and increasing problem in Saskatchewan’s livestock. Chronic exposure to low concentrations of ergot alkaloids is known to cause severe arterial vasoconstriction and gangrene through the activation of adrenergic and serotonergic receptors on vascular smooth muscles. The acute vascular effects of a single oral dose with high-level exposure to ergot alkaloids remain unknown and are examined in this study. This study had two main objectives; the first was to evaluate the role of α1-adrenergic receptors in mediating the acute vasocontractile response after single-dose exposure in sheep. The second was to examine whether terazosin (TE) could abolish the vascular contractile effects of ergot alkaloids. Twelve adult female sheep were randomly placed into control and exposure groups (n = 6/group). Ergot sclerotia were collected and finely ground. The concentrations of six ergot alkaloids (ergocornine, ergocristine, ergocryptine, ergometrine, ergosine, and ergotamine) were determined using HPLC/MS at Prairie Diagnostic Services Inc., (Saskatoon, SK, Canada). Each ewe within the treatment group received a single oral treatment of ground ergot sclerotia at a dose of 600 µg/kg BW (total ergot) while each ewe in the control group received water. Animals were euthanized 12 h after the treatment, and the pedal artery (dorsal metatarsal III artery) from the left hind limb from each animal was carefully dissected and mounted in an isolated tissue bath. The vascular contractile response to phenylephrine (PE) (α1-adrenergic agonist) was compared between the two groups before and after TE (α1-adrenergic antagonist) treatment. Acute exposure to ergot alkaloids resulted in a 38% increase in vascular sensitivity to PE compared to control (Ctl EC50 = 1.74 × 10−6 M; Exp EC50 = 1.079 × 10−6 M, p = 0.046). TE treatment resulted in a significant dose-dependent increase in EC50 in both exposure and control groups (p < 0.05 for all treatments). Surprisingly, TE effect was significantly more pronounced in the ergot exposed group compared to the control group at two of the three concentrations of TE (TE 30 nM, p = 0.36; TE 100 nM, p < 0.001; TE 300 nM, p < 0.001). Similar to chronic exposure, acute exposure to ergot alkaloids results in increased vascular sensitivity to PE. TE is a more potent dose-dependent antagonist for the PE contractile response in sheep exposed to ergot compared to the control group. This study may indicate that the dry gangrene seen in sheep, and likely other species, might be related to the activation of α1-adrenergic receptor. This effect may be reversed using TE, especially at early stages of the disease before cell death occurs. This study may also indicate that acute-single dose exposure scenario may be useful in the study of vascular effects of ergot alkaloids.

scholarly journals Laminar shear stress upregulates endothelial Ca2+-activated K+ channels KCa2.3 and KCa3.1 via a Ca2+/calmodulin-dependent protein kinase kinase/Akt/p300 cascade

2013 ◽  
Vol 305 (4) ◽  
pp. H484-H493 ◽  
Author(s):  
Jun Takai ◽  
Alexandra Santu ◽  
Haifeng Zheng ◽  
Sang Don Koh ◽  
Masanori Ohta ◽  
...  
Keyword(s):  
Shear Stress ◽  
Transcriptional Activation ◽  
Static Condition ◽  
Fold Increase ◽  
Laminar Shear Stress ◽  
Human Coronary Artery ◽  
Intracellular Ca ◽  
Kinase Cascade ◽  
Dependent Protein ◽  
Laminar Shear

In endothelial cells (ECs), Ca2+-activated K+ channels KCa2.3 and KCa3.1 play a crucial role in the regulation of arterial tone via producing NO and endothelium-derived hyperpolarizing factors. Since a rise in intracellular Ca2+ levels and activation of p300 histone acetyltransferase are early EC responses to laminar shear stress (LS) for the transcriptional activation of genes, we examined the role of Ca2+/calmodulin-dependent kinase kinase (CaMKK), the most upstream element of a Ca2+/calmodulin-kinase cascade, and p300 in LS-dependent regulation of KCa2.3 and KCa3.1 in ECs. Exposure to LS (15 dyn/cm2) for 24 h markedly increased KCa2.3 and KCa3.1 mRNA expression in cultured human coronary artery ECs (3.2 ± 0.4 and 45 ± 10 fold increase, respectively; P < 0.05 vs. static condition; n = 8–30), whereas oscillatory shear (OS; ± 5 dyn/cm2 × 1 Hz) moderately increased KCa3.1 but did not affect KCa2.3. Expression of KCa2.1 and KCa2.2 was suppressed under both LS and OS conditions, whereas KCa1.1 was slightly elevated in LS and unchanged in OS. Inhibition of CaMKK attenuated LS-induced increases in the expression and channel activity of KCa2.3 and KCa3.1, and in phosphorylation of Akt (Ser473) and p300 (Ser1834). Inhibition of Akt abolished the upregulation of these channels by diminishing p300 phosphorylation. Consistently, disruption of the interaction of p300 with transcription factors eliminated the induction of these channels. Thus a CaMKK/Akt/p300 cascade plays an important role in LS-dependent induction of KCa2.3 and KCa3.1 expression, thereby regulating EC function and adaptation to hemodynamic changes.

Regulation of intracellular calcium in N1E-115 neuroblastoma cells: the role of Na+/Ca2+exchange

2002 ◽  
Vol 282 (5) ◽  
pp. C1000-C1008 ◽  
Author(s):  
Kara L. Kopper ◽  
Joseph S. Adorante
Keyword(s):  
Membrane Potential ◽  
Intracellular Calcium ◽  
Normal Cell ◽  
Buffer Capacity ◽  
Neuroblastoma Cells ◽  
Fold Increase ◽  
Scorpion Venom ◽  
Reverse Mode ◽  
Intracellular Ca

In fura 2-loaded N1E-115 cells, regulation of intracellular Ca2+ concentration ([Ca2+]i) following a Ca2+ load induced by 1 μM thapsigargin and 10 μM carbonylcyanide p-trifluoromethyoxyphenylhydrazone (FCCP) was Na+ dependent and inhibited by 5 mM Ni2+. In cells with normal intracellular Na+ concentration ([Na+]i), removal of bath Na+, which should result in reversal of Na+/Ca2+exchange, did not increase [Ca2+]i unless cell Ca2+ buffer capacity was reduced. When N1E-115 cells were Na+ loaded using 100 μM veratridine and 4 μg/ml scorpion venom, the rate of the reverse mode of the Na+/Ca2+ exchanger was apparently enhanced, since an ∼4- to 6-fold increase in [Ca2+]ioccurred despite normal cell Ca2+ buffering. In SBFI-loaded cells, we were able to demonstrate forward operation of the Na+/Ca2+ exchanger (net efflux of Ca2+) by observing increases (∼ 6 mM) in [Na+]i. These Ni2+ (5 mM)-inhibited increases in [Na+]i could only be observed when a continuous ionomycin-induced influx of Ca2+ occurred. The voltage-sensitive dye bis-(1,3-diethylthiobarbituric acid) trimethine oxonol was used to measure changes in membrane potential. Ionomycin (1 μM) depolarized N1E-115 cells (∼25 mV). This depolarization was Na+dependent and blocked by 5 mM Ni2+ and 250–500 μM benzamil. These data provide evidence for the presence of an electrogenic Na+/Ca2+ exchanger that is capable of regulating [Ca2+]i after release of Ca2+ from cell stores.

Biochemical studies of intrauterine components of the tammar wallaby Macropus eugenii during pregnancy

Development ◽  
1981 ◽  
Vol 62 (1) ◽  
pp. 325-338
Author(s):  
Elizabeth J. Thornber ◽  
Marilyn B. Renfree ◽  
Gregory I. Wallace
Keyword(s):  
Protein Concentration ◽  
Specific Binding ◽  
Polyacrylamide Gel Electrophoresis ◽  
Fold Increase ◽  
Tammar Wallaby ◽  
Macropus Eugenii ◽  
Tenfold Increase ◽  
Specific Proteins ◽  
Wet Weight

The in vitro uptake and incorporation of [3H]ui idine by blastocysts of the tammar wallaby showed a 16- and 30-fold increase from day 0 to day 10 after removal of pouch young, respectively. Two of the six non-expanded blastocysts recovered on day 5 showed a tenfold increase in incorporation. During the first ten days after removal of pouch young the diameter of the blastocyst increased threefold. Endometrial exudate from gravid uteri had a higher protein concentration than exudate from nongravid uteri (39·5 ± 0·9 and 32·0 ± 2·0 mg/ml (mean ± s.e.m.), respectively). Endometrial exudates from uteri where the blastocyst was actively growing were found to contain six uterine-specific proteins. These were separated by gradient polyacrylamide gel electrophoresis. Two of the proteins were pre-albumins and the others were larger molecules (M.W. 153000–670000). Two proteins were only present at particular stages of pregnancy: the other four were present at all stages from diapause to birth, in exudate from gravid and nongravid uteri. The specific binding of progesterone and androstenedione to proteins in endometrial exudates or uterine flushings from pregnant wallabies was less than one per cent of the value obtained from day-5 pregnant rabbits. The ability of mouse blastocysts to take up and incorporate [3H]uridine into acidinsoluble material increased threefold in the presence of day-10 endometrial exudates from wallabies. However, this was less than ten percent of the values obtained in the presence of bovine serum albumin. The concentration of calcium in endometrial exudates increased from 23·6 to 45·2 μg/ml during pregnancy; in endometrium it remained at 88·7 μg/g (wet weight) throughout pregnancy, and in plasma it was 53·3 μg/ml. The concentration of zinc in endometrial exudates was 4·5 μg/ml; in endometrium it decreased from 21·8 to 13·3 μg/g (wet weight) during pregnancy and in plasma it was 0·6 μg/ml.

The agouti gene product stimulates pancreatic β-cell Ca2+ signaling and insulin release

1999 ◽  
Vol 1 (1) ◽  
pp. 11-19 ◽  
Author(s):  
B. Z. XUE ◽  
W. O. WILKISON ◽  
R. L. MYNATT ◽  
N. MOUSTAID ◽  
M. GOLDMAN ◽  
...  
Keyword(s):  
Gene Product ◽  
Insulin Release ◽  
Fold Increase ◽  
Cell Types ◽  
Human Pancreas ◽  
Pancreatic Β Cell ◽  
Β Cell ◽  
Agouti Protein ◽  
Intracellular Ca ◽  
Agouti Gene

Xue, B. Z., W. O. Wilkison, R. L. Mynatt, N. Moustaid, M. Goldman, and M. B. Zemel. The agouti gene product stimulates pancreatic β-cell Ca2+ signaling and insulin release. Physiol. Genomics 1: 11-19, 1999.—Ubiquitous expression of the mouse agouti gene results in obesity and hyperinsulinemia. Human agouti is expressed in adipose tissue, and we found recombinant agouti protein to stimulate lipogenesis in adipocytes in a Ca2+-dependent fashion. However, adipocyte-specific agouti transgenic mice only became obese in the presence of hyperinsulinemia. Because intracellular Ca2+ concentration ([Ca2+]i) is a primary signal for insulin release, and we have shown agouti protein to increase [Ca2+]i in several cell types, we examined the effects of agouti on [Ca2+]i and insulin release. We demonstrated the expression of agouti in human pancreas and generated recombinant agouti to study its effects on Ca2+ signaling and insulin release. Agouti (100 nM) stimulated Ca2+ influx, [Ca2+]i increase, and a marked stimulation of insulin release in two β-cell lines (RIN-5F and HIT-T15; P < 0.05). Agouti exerted comparable effects in isolated human pancreatic islets and β-cells, with a 5-fold increase in Ca2+ influx ( P < 0.001) and a 2.2-fold increase in insulin release ( P < 0.01). These data suggest a potential role for agouti in the development of hyperinsulinemia in humans.

Mechanosensitive afferents of femoral-saphenous vein

1987 ◽  
Vol 252 (2) ◽  
pp. R367-R370 ◽  
Author(s):  
P. W. Davenport ◽  
F. J. Thompson
Keyword(s):  
Endothelial Cells ◽  
Smooth Muscle ◽  
Contractile Response ◽  
Blocking Agent ◽  
Urotensin Ii ◽  
Dibutyryl Cyclic Amp ◽  
Maximal Contraction ◽  
Channel Blocking ◽  
Apparent Concentration ◽  
Small Contraction

Urotensin II (U II) caused marked concentration-dependent contractions of helical strips from several major arteries of the rat. The thoracic aorta was most sensitive; the apparent concentration of U II producing half-maximal contraction was 6.8 X 10(-10) M. Papaverine, dibutyryl cyclic AMP, forskolin, and nitroprusside antagonized the contractile responses to U II at the apparent concentrations producing 50% inhibition (IC50) of 7.6 X 10(-6), 2.1 X 10(-4), 2.5 X 10(-6), and 1.5 X 10(-8) M, respectively. Verapamil, a calcium channel-blocking agent, partially inhibited the contractile response to U II at IC50 = 6.5 X 10(-6) M. Maximal relaxation, i.e., a complete inhibition, could not be obtained even at a concentration of 3 X 10(-5) M verapamil. Cyproheptadine reduced the U II-induced contraction at higher concentrations. Phentolamine (10(-5) M), propranolol (10(-5) M), atropine (10(-4) M), tetrodotoxin (10(-6) M), burimamide (10(-5) M), and indomethacin (10(-5) M) did not change the U II-induced contraction. At higher concentration, U II (10(-8) M) induced a small contraction of aortic strips in Ca2+-free Krebs Henseleit solution similar to that of norepinephrine, but the U II-induced contraction was not inhibited by phentolamine or propranolol. The action of U II did not require the presence of endothelial cells. It is concluded that U II acts on vascular smooth muscle and induces the contraction partly through intracellular Ca2+ mobilization but mainly by stimulating the influx of extracellular Ca2+ via potential dependent and potential independent calcium channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Ca2+ sensitization during sustained hypoxic pulmonary vasoconstriction is endothelium dependent

2003 ◽  
Vol 284 (6) ◽  
pp. L1121-L1126 ◽  
Author(s):  
Tom P. Robertson ◽  
Philip I. Aaronson ◽  
Jeremy P. T. Ward
Keyword(s):  
Hypoxic Pulmonary Vasoconstriction ◽  
Mesenteric Arteries ◽  
Initial Transient ◽  
Endothelin 1 ◽  
Pulmonary Vasoconstriction ◽  
Endothelial Denudation ◽  
Transient Rise ◽  
Intracellular Ca ◽  
Prostaglandin F

The main aim of this study was to determine the effects of endothelium removal on tension and intracellular Ca2+([Ca2+]i) during hypoxic pulmonary vasoconstriction (HPV) in rat isolated intrapulmonary arteries (IPA). Rat IPA and mesenteric arteries (MA) were mounted on myographs and loaded with the Ca2+-sensitive fluorophore fura PE-3. Arteries were precontracted with prostaglandin F2α, and the effects of hypoxia were examined. HPV in isolated IPA consisted of a transient constriction superimposed on a second sustained phase. Only the latter phase was abolished by endothelial denudation. However, removal of the endothelium had no effect on [Ca2+]i at any point during HPV. The endothelin-1 antagonists BQ-123 and BQ-788 did not affect HPV, although constriction induced by 100 nM endothelin-1 was abolished. In MA, hypoxia induced an initial transient rise in tension and [Ca2+]i, followed by vasodilatation and a fall in [Ca2+]i to (but not below) prehypoxic levels. These results are consistent with sustained HPV being mediated by an endothelium-derived constrictor factor that is distinct from endothelin-1 and that elicits vasoconstriction via Ca2+sensitization.

Angiotensin II and bladder obstruction in the rat: influence on hypertrophic growth and contractility

1996 ◽  
Vol 271 (5) ◽  
pp. R1186-R1192 ◽  
Author(s):  
K. Persson ◽  
R. K. Pandita ◽  
K. Waldeck ◽  
K. E. Andersson
Keyword(s):  
Angiotensin Ii ◽  
Protein Content ◽  
Contractile Response ◽  
Fold Increase ◽  
Urethral Obstruction ◽  
Bladder Function ◽  
Ang Ii ◽  
Hypertrophic Growth ◽  
Bladder Obstruction ◽  
Bladder Weight

The mechanisms and mediators of hypertrophic growth secondary to infravesical urinary outflow obstruction are unknown. The renin-angiotensin system has been implicated in vascular and cardiac hypertrophy, but the involvement of angiotensin II (ANG II) as a trophic factor in the lower urinary tract has not been investigated. In this study, the ANG II subtype AT1 receptor antagonist losartan (DuP 753) was administered perorally (15 mg.kg-1.day-1) for 28 days to rats subjected to partial urethral obstruction or sham surgery. Partial urethral obstruction caused a 3.5-fold increase in bladder weight and a 3-fold increase in bladder protein content compared with sham rats. However, no difference was observed in bladder weight or bladder protein content between losartan-treated rats and rats receiving no drug. Cystometric evaluation of bladder function revealed significant increases in micturition volume, bladder capacity, bladder compliance, and spontaneous contractile activity in rats subjected to partial urethral obstruction compared with sham rats. However, bladder function in rats treated with losartan was not different from bladder function in rats receiving no drug. In vitro studies of isolated bladder tissue showed a weak contractile response to ANG II (1 microM) that amounted to 4.4 +/- 1.0% of the response to K+ (124 mM). The ANG II-induced contraction was abolished by losartan (10 microM) and indomethacin (10 microM). The contractile response to ANG II (1 microM), K+ (124 mM), and transmural nerve stimulation (2 Hz) was reduced in bladder strips from obstructed rats. In conclusion, no evidence was found for involvement of ANG II in development of bladder hypertrophy. The effect of ANG II on bladder smooth muscle tone was minor but was mediated by stimulation of the AT1 subtype receptor.

Inhibition of endothelium-dependent vasorelaxation by extracellular K+: a novel controlling signal for vascular contractility

2004 ◽  
Vol 286 (1) ◽  
pp. H329-H339 ◽  
Author(s):  
Geun Hee Seol ◽  
Seung Cheol Ahn ◽  
Ji Aee Kim ◽  
Bernd Nilius ◽  
Suk Hyo Suh
Keyword(s):  
Endothelial Cells ◽  
Membrane Potential ◽  
Umbilical Vein ◽  
Vascular Contractility ◽  
Vasoactive Factors ◽  
Intracellular Ca ◽  
Prostaglandin F ◽  
Umbilical Vein Endothelial Cells ◽  
Mouse Aorta ◽  
Endothelium Dependent Relaxation

The effects of extracellular K+ on endothelium-dependent relaxation (EDR) and on intracellular Ca2+ concentration ([Ca2+]i) were examined in mouse aorta, mouse aorta endothelial cells (MAEC), and human umbilical vein endothelial cells (HUVEC). In mouse aortic rings precontracted with prostaglandin F2α or norepinephrine, an increase in extracellular K+ concentration ([K+]o) from 6 to 12 mM inhibited EDR concentration dependently. In endothelial cells, an increase in [K+]o inhibited the agonist-induced [Ca2+]i increase concentration dependently. Similar to K+, Cs+ also inhibited EDR and the increase in [Ca2+]i concentration dependently. In current-clamped HUVEC, increasing [K+]o from 6 to 12 mM depolarized membrane potential from –32.8 ± 2.7 to –8.6 ± 4.9 mV ( n = 8). In voltage-clamped HUVEC, depolarizing the holding potential from –50 to –25 mV decreased [Ca2+]i significantly from 0.95 ± 0.03 to 0.88 ± 0.03 μM ( n = 11, P < 0.01) and further decreased [Ca2+]i to 0.47 ± 0.04 μM by depolarizing the holding potential from –25 to 0 mV ( n = 11, P < 0.001). Tetraethylammonium (1 mM) inhibited EDR and the ATP-induced [Ca2+]i increase in voltage-clamped MAEC. The intermediate-conductance Ca2+-activated K+ channel openers 1-ethyl-2-benzimidazolinone, chlorozoxazone, and zoxazolamine reversed the K+-induced inhibition of EDR and increase in [Ca2+]i. The K+-induced inhibition of EDR and increase in [Ca2+]i was abolished by the Na+-K+ pump inhibitor ouabain (10 μM). These results indicate that an increase of [K+]o in the physiological range (6–12 mM) inhibits [Ca2+]i increase in endothelial cells and diminishes EDR by depolarizing the membrane potential, decreasing K+ efflux, and activating the Na+-K+ pump, thereby modulating the release of endothelium-derived vasoactive factors from endothelial cells and vasomotor tone.

Ca2+ and protein kinase C activation of mucin granule exocytosis in permeabilized SPOC1 cells

1998 ◽  
Vol 275 (1) ◽  
pp. C285-C292 ◽  
Author(s):  
C. E. Scott ◽  
Lubna H. Abdullah ◽  
C. William Davis
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Fold Increase ◽  
Mucin Secretion ◽  
Granule Exocytosis ◽  
Kinase C ◽  
Streptolysin O ◽  
Intracellular Ca ◽  
Mucin Release ◽  
Protein Kinase C Activation

Mucin secretion by airway goblet cells is under the control of apical P2Y2, phospholipase C-coupled purinergic receptors. In SPOC1 cells, the mobilization of intracellular Ca2+ by ionomycin or the activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) stimulates mucin secretion in a fully additive fashion [L. H. Abdullah, J. D. Conway, J. A. Cohn, and C. W. Davis. Am. J. Physiol. 273 ( Lung Cell. Mol. Physiol. 17): L201–L210, 1997]. This apparent independence between PKC and Ca2+ in the stimulation of mucin secretion was tested in streptolysin O-permeabilized SPOC1 cells. These cells were fully competent to secrete mucin when Ca2+ was elevated from 100 nM to 3.1 μM for 2 min following permeabilization; the Ca2+EC50 was 2.29 ± 0.07 μM. Permeabilized SPOC1 cells were exposed to PMA or 4α-phorbol at Ca2+ activities ranging from 10 nM to 10 μM. PMA, but not 4α-phorbol, increased mucin release at all Ca2+ activities tested: at 10 nM Ca2+ mucin release was 2.1-fold greater than control and at 4.7 μM Ca2+ mucin release was maximal (3.6-fold increase). PMA stimulated 27% more mucin release at 4.7 μM than at 10 nM Ca2+. Hence, SPOC1 cells possess Ca2+-insensitive, PKC-dependent, and Ca2+-dependent PKC-potentiated pathways for mucin granule exocytosis.

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