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Query: UNIPROT:P01185 (vasopressin)
 23,126 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The inflow of Mn2+ across the plasma membranes of isolated hepatocytes was monitored by measuring the quenching of the fluorescence of intracellular quin2, by atomic absorption spectroscopy and by the uptake of 54Mn2+. The inflow of other divalent metal ions was measured using quin2. 2. Under ionic conditions which resembled those present in the cytoplasmic space, Mn2+, Zn2+, Co2+, Ni2+ and Cd2+ each quenched the fluorescence of a solution of Ca2(+)-quin2. 3. The addition of Mn2+, Zn2+, Co2+, Ni2+ or Cd2+ to cells loaded with quin2 caused a time-dependent decrease in the fluorescence of intracellular quin2. Plots of the rate of decrease in fluorescence as a function of the concentration of Mn2+ reached a plateau at 100 microM-Mn2+. 4. The rate of decrease in fluorescence induced by Mn2+ was stimulated by 20% in the presence of vasopressin. The effect of vasopressin was completely inhibited by 200 microM-verapamil. Adrenaline, angiotensin II and glucagon also stimulated the rate of decrease in the fluorescence of intracellular quin2 induced by Mn2+. 5. The rate of decrease in fluorescence induced by Zn2+, Co2+, Ni2+ or Cd2+ was stimulated by between 20 and 190% in the presence of vasopressin or angiotensin II. 6. The rates of uptake of Mn2+ measured by atomic absorption spectroscopy or by using 54Mn2+ were inhibited by about 20% by 1.3 mM-Ca2+o and stimulated by 30% by vasopressin. 7. Plots of Mn2+ uptake, measured by atomic absorption spectroscopy or with 54Mn2+, as a function of the extracellular concentration of Mn2+ were biphasic over the range 0.05-1.0 mM added Mn2+ and did not reach a plateau at 1.0 mM-Mn2+. 8. It is concluded that (i) hepatocytes possess both a basal and a receptor-activated divalent cation inflow system, each of which has a broad specificity for metal ions, and (ii) the receptor-activated divalent cation inflow system is the receptor-operated Ca2+ channel.
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PMID:The liver cell plasma membrane Ca2+ inflow systems exhibit a broad specificity for divalent metal ions. 216 60

Agonist-stimulated divalent cation entry was studied in fura-2-loaded hepatocytes. In the presence of extracellular Mn2+, the Ca2(+)-mobilizing hormone vasopressin produced a severalfold stimulation of the basal rate of fura-2 fluorescence quenching as a result of Mn2+ influx; this effect was blocked by the presence of Ni2+ in the incubation medium. Half-maximum and maximum stimulation of Mn2+ influx was observed with 0.1 and 0.8 nM vasopressin, respectively. Agonist-stimulated Mn2+ influx was also seen with angiotensin II, ATP, phenylephrine, and the combination of AlCl3 and NaF. The stimulation of Mn2+ influx did not occur immediately after addition of Ca2(+)-mobilizing agents, but was characterized by a latency period of 20-30 s. In contrast to vasopressin, glucagon did not stimulate Mn2+ influx into hepatocytes, but produced both a 3-fold enhancement of the rate of vasopressin-stimulated Mn2+ entry and the abolishment of the latency period. The effects of glucagon were mimicked by forskolin and dibutyryl cAMP. Pretreatment of hepatocytes with pertussis toxin or depolarization of the cells altered neither the basal rate of Mn2+ entry nor the ability of vasopressin to stimulate this rate. Emptying of the inositol 1,4,5-trisphosphate-sensitive Ca2+ store by treatment with 2,5-di-(tert-butyl)-1,4-benzohydroquinone (tBuBHQ) did not enhance Mn2+ entry into hepatocytes; however, exposure of the cells to tBuBHQ for 2 min markedly enhanced the ability of vasopressin, alone or in combination with glucagon, to increase the rate of Mn2+ influx. Furthermore, pretreatment with tBuBHQ for 2 min abolished the latency of vasopressin-stimulated Mn2+ influx. It is concluded that Ca2(+)-mobilizing hormones stimulate Ca2+ influx in hepatocytes, possibly through receptor-operated Ca2+ channels. The stimulation of divalent cation entry is transduced by a G protein, and the rate of influx appears to be controlled both by the intracellular level of cAMP and the empty state of an intracellular Ca2+ pool that may be inositol 1,4,5-trisphosphate-insensitive.
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PMID:Receptor-operated calcium influx in rat hepatocytes. Identification and characterization using manganese. 217 Mar 82

1. The properties of intracellular Ca2+ stores of intact- and of saponin-skinned A7r5 (an established cell line from embryonic rat aorta) smooth muscle cells were studied by measuring 45Ca2+ and 54Mn2+ fluxes. 2. Application of 5 microM-vasopressin to intact cells increased the fractional loss of 45Ca2+ in Ca2(+)-free solution by a factor of 5.2. This effect was not influenced by a pre-incubation with 10 microM-ryanodine. Caffeine (25 mM) did not stimulate the fractional loss of 45Ca2+ from intact cells. 3. In skinned cells 10 microM-IP3 (inositol 1,4,5-trisphosphate) and 5 microM-A23187 (a calcium ionophore) released the same amount of 45Ca2+. This release did not require GTP and was not affected by a pre-incubation with 10 microM-ryanodine. Caffeine (25 mM) did not release stored Ca2+. 4. NaF (1 mM) plus 10 microM-AlCl3 inhibited by 72% the 45Ca2+ uptake by the IP3-sensitive store of skinned cells at 0.15 microM-Ca2+. Cyclic AMP-dependent protein kinase did not stimulate this ATP-dependent 45Ca2+ uptake, nor could the presence of phospholamban be demonstrated immunologically. 5. The 45Ca2+ uptake by cells which had been depleted of Ca2+ with 5 microM-vasopressin was 69% higher than the uptake obtained without such proceeding depletion. This enhanced 45Ca2+ uptake did not occur through voltage-operated Ca2+ channels, because blockade of these channels with verapamil, or depolarization of the plasma membrane by increasing [K+] from 5.9 to 59 mM in the presence of verapamil, did not modify this uptake. 6. A similar increase of the 54Mn2+ uptake occurred in intact cells with a depleted Ca2+ store. If, however, the cells were first skinned and subsequently exposed to 54Mn2+, the ATP-dependent 54Mn2+ uptake amounted to less than 6% of the ATP-dependent 45Ca2+ uptake. 7. If intact cells were first exposed to a 45Ca2(+)- or 54Mn2(+)-containing solution, and subsequently skinned in a non-radioactive intracellular solution, the addition of 10 microM-A23187 to these cells released stored Ca2+ or Mn2+. The amount of released Ca2+ was only slightly larger than the amount of released Mn2+. If the intracellular store was depleted before loading, the amount of Ca2+ or Mn2+ released by the ionophore increased by 68 and 28%, respectively. 8. It is concluded that A7r5 smooth muscle cells do not express a Ca2(+)-induced Ca2+ release mechanism, but do contain an IP3-induced Ca2+ release mechanism which can release approximately all intracellularly accumulated 45Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Agonist-dependent Ca2+ and Mn2+ entry dependent on state of filling of Ca2+ stores in aortic smooth muscle cells of the rat. 221 95

The ability of alpha-adrenergic agonists and vasopressin to increase the mitochondrial volume in hepatocytes is dependent on the presence of extracellular Ca2+. Addition of Ca2+ to hormone-treated cells incubated in the absence of Ca2+ initiates mitochondrial swelling. In the presence of extracellular Ca2+, A23187 (7.5 microM) induces mitochondrial swelling and stimulates gluconeogenesis from L-lactate. Isolated liver mitochondria incubated in KCl medium in the presence of 2.5 mM-phosphate undergo energy-dependent swelling, which is associated with electrogenic K+ uptake and reaches an equilibrium when the volume has increased to about 1.3-1.5 microliter/mg of protein. This K+-dependent swelling is stimulated by the presence of 0.3-1.0 microM-Ca2+, leading to an increase in matrix volume at equilibrium that is dependent on [Ca2+]. Ca2+-activated K+-dependent swelling requires phosphate and shows a strong preference for K+ over Na+, Li+ or choline. It is not associated with either uncoupling of mitochondria or any non-specific permeability changes and cannot be produced by Ba2+, Mn2+ or Sr2+. Ca2+-activated K+-dependent swelling is not prevented by any known inhibitors of plasma-membrane ion-transport systems, nor by inhibitors of mitochondrial phospholipase A2. Swelling is inhibited by 65% and 35% by 1 mM-ATP and 100 microM-quinine respectively. The effect of Ca2+ is blocked by Ruthenium Red (5 micrograms/ml) at low [Ca2+]. Spermine (0.25 mM) enhanced the swelling seen on addition of Ca2+, correlating with its ability to increase Ca2+ uptake into the mitochondria as measured by using Arsenazo-III. Mitochondria derived from rats treated with glucagon showed less swelling than did control mitochondria. In the presence of Ruthenium Red and higher [Ca2+], the mitochondria from hormone-treated animals showed greater swelling than did control mitochondria. These data imply that an increase in intramitochondrial [Ca2+] can increase the electrogenic flux of K+ into mitochondria by an unknown mechanism and thereby cause swelling. It is proposed that this is the mechanism by which alpha-agonists and vasopressin cause an increase in mitochondrial volume in situ.
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PMID:Regulation of the mitochondrial matrix volume in vivo and in vitro. The role of calcium. 243 81

1. Isolated neurosecretory nerve endings were prepared from rat neurohypophyses. The amount of vasopressin (AVP) and oxytocin released was measured by radioimmunoassay. 2. The amount of hormone release under resting conditions was not affected by external calcium (Ca2+o). Secretion decreased by ca. 50% when external sodium (Na+o) was replaced by choline or sucrose. 3. Ouabain did not modify the basal AVP release. 4. The Na+ ionophore monensin increased the release of AVP only in the presence of Na+o. This increase was maintained during prolonged exposure to the ionophore and occurred in the presence of Ca2+o only. 5. In the presence of Ca2+o, the amount of evoked hormone release was dependent on the external K+ concentration. Half-maximal activation was achieved with ca. 40 mM-K+. The K+-induced secretion was potentiated in Na+-free solution. 6. Prolonged 100 mM-K+-induced depolarization in the presence of Ca2+o gave rise to a large increase in hormone secretion which decreased with time (t1/2 = 2.5 min). The release could be reactivated after permeabilization of the nerve terminals in the presence of micromolar concentrations of Ca2+. 7. A stepwise paradigm in which Ko+ is incrementally increased to 25, 50, 75 and then 100 mM released more AVP than a prolonged exposure to 100 mM-K+. 8. Veratridine increased the amount of AVP released. This effect was considerably reduced in the absence of Nao+ and abolished in the presence of D600. 9. The depolarization-induced AVP release was blocked by different Ca2+-antagonists. Their effectiveness was nitrendipine = nicardipine greater than Cd2+ greater than Gd3+ greater than Co2+ = Mn2+. 10. The dihydropyridine Bay K 8644 potentiated both the basal and the K+-evoked AVP release. Its maximal effect was obtained with 25-50 mM-Ko+. 11. In conclusion, the isolated neurohypophysial terminals which have both Na+ and Ca2+ channels and release AVP and oxytocin upon depolarization might be an excellent system to study further the mechanisms leading to secretion of neurohormones.
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PMID:Hormone release from isolated nerve endings of the rat neurohypophysis. 245 Sep 99

The extracellular Ca2+ dependence of agonist stimulation of vascular smooth muscle (VSM) has been investigated in rat cultured aortic smooth muscle cells (SMCs) and isolated mesenteric resistance vessels (MRVs). Agonists such as [Arg8]vasopressin (AVP), angiotensin II (Ang II), and adenosine-5'-triphosphate (ATP) stimulated 45Ca2+ entry into the SMCs that was (a) independent of the extent to which the membranes were polarized, and (b) was not inhibited by organic Ca2+ channel antagonists. Measuring the intracellular Ca2+ concentration [( Ca2+]i) after stimulation with agonists revealed a rapid increase of [Ca2+]i, which was followed by a sustained rise that was insensitive to Ca2+ antagonists. In Ca2+-free medium, only the initial peak of [Ca2+]i was still observed, but the sustained response to the agonists disappeared completely. This observation indicates that the sustained elevation seen in Ca2+-containing medium was the consequence of agonist-induced Ca2+ entry. In MRVs, a corresponding Ca2+-antagonist-insensitive, agonist (norepinephrine and AVP)-induced tonic tension was also identified. Moreover, agonists were able to induce sustained tension in the MRVs regardless of whether the membrane was normally polarized or was previously depolarized (80 mM K+) upon their administration. The agonist-stimulated 45Ca2+ entry in the SMCs could be blocked by the multivalent cations La3+, Cd2+, Mn2+, Co2+, Ni2+, and Mg2+ (in this order of potency). Depolarization-induced 45Ca2+ influx was inhibited by these cations in the same order of potency, but was significantly more sensitive to Cd2+ and significantly less sensitive to La3+ than that stimulated by agonists. Treatment with 2-nitro-4-carboxyphenyl-N,N-diphenyl-carbamate (NCDC, a proposed inhibitor of phospholipase C) reduced both the agonist-induced 45Ca2+ influx and the sustained elevation of [Ca2+]i in the SMCs. NCDC also abolished both contraction and depolarization induced by agonists in the MRVs. The kinase C stimulator phorbol-12-myristate-13-acetate (PMA) inhibited the agonist-induced 45Ca2+ influx and sustained increase in [Ca2+]i in the SMCs, whereas the kinase C inhibitor staurosporine had no effect. In the MRVs, in contrast, PMA had no influence on agonist-induced contractions. Staurosporine (1 microM), however, completely prevented these contractions, as did NCDC, but, unlike NCDC, it did so without affecting the agonist-induced depolarization. These data support an important role of receptor-operated Ca2+-permeable channels in VSM activation by agonists and suggest that these channels may be controlled by intracellular enzymic pathways and second messenger systems.
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PMID:Receptor-operated calcium-permeable channels in vascular smooth muscle. 247 25

The properties of the receptor-activated Ca2+ inflow system in the liver cell plasma membrane were compared with those of voltage-operated Ca2+ channels and receptor-operated Ca2+ channels present in other cell types by testing the susceptibility of the Ca2+ inflow system to inhibition by other metal ions and known inhibitors of Ca2+ movement across membranes. Co2+ inhibited Ca2+ inflow through the receptor-activated Ca2+ inflow system, as assessed by measurement of (a) the activation by extracellular Ca2+ (Cao2+) of glycogen phosphorylase in the presence of vasopressin and (b) 45Ca2+ exchange in the presence of the hormone. The concentration of Co2+ which gave half-maximal inhibition was 280 microM. The inhibition by Co2+ was reversed by high Cao2+. Co2+ did not inhibit basal Ca2+ inflow as measured by 45Ca2+ exchange in the absence of vasopressin. Zn2+, Cd2+, Ni2+ and Mn2+ each inhibited Ca2+ inflow through the receptor-activated Ca2+ inflow system. The concentrations of these ions which gave half-maximal inhibition were 10, 50, 220 and 400 microM, respectively. Little inhibition of receptor-activated Ca2+ inflow was observed in the presence of Sr2+ or Ba2+. However, substantial amounts of 90Sr2+ were taken up by hepatocytes. Rates of 90Sr2+ uptake increased from 0.5-8 nmol per min per mg wet wt. when the extracellular concentration of Sr2+ was varied from 0.25 to 2.5 mM. Sr2+ uptake was inhibited 50% by Cao2+ with half-maximal inhibition at 100 microM Cao2+, but was not inhibited by verapamil and was not stimulated by vasopressin. The movement of Ca2+ through the receptor-activated Ca2+ inflow system was not inhibited by high concentrations of each of a number of inhibitors of voltage-operated and receptor-operated Ca2+ channels and intracellular Ca2+ movement. It is concluded that while the susceptibility to inhibition by metal ions of the receptor-activated Ca2+ inflow system in the liver cell plasma membrane is similar to that of voltage-operated Ca2+ channels, there are significant differences between the liver cell receptor-activated Ca2+ inflow system and both voltage-operated Ca2+ channels and some other receptor-operated Ca2+ channels with respect to inhibition by organic compounds.
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PMID:Inhibition of the liver cell receptor-activated Ca2+ inflow system by metal ion inhibitors of voltage-operated Ca2+ channels but not by other inhibitors of Ca2+ inflow. 255 3

Oxytocin-binding sites in the endometrium and myometrium of the non-pregnant ewe were characterized. [3H]Oxytocin bound to a single site in both tissues with high affinity; dissociation constants were determined to be 1.96 nmol/l in endometrium and 2.12 nmol/l in myometrium. Oxytocin binding was enhanced by divalent cations with a similar order of potency in both tissues: Co2+ greater than Mn2+ greater than Ni2+ greater than Mg2+ greater than Zn2+ greater than Ca2+. The endometrial and myometrial binding sites showed the same specificity for oxytocin analogues and related peptides, having high affinity for oxytocin, [Arg8]-vasopressin, [Lys8]-vasopressin, and the oxytocin-specific agonists [Gly7]-oxytocin and [Thr4,Gly7]-oxytocin. The results suggest that oxytocin receptors present in the endometrium and myometrium of the ewe are similar both to each other and to classical oxytocin receptors.
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PMID:Characterization of endometrial and myometrial oxytocin receptors in the non-pregnant ewe. 255 41

To evaluate a possible modulation by membrane fluidity of hormonal, cAMP-mediated effects on renal epithelial cells, we studied the effect of the neutral local anesthetic, benzyl alcohol, on membrane fluidity and on basal and stimulated intracellular cAMP content in intact MDCK cells. Benzyl alcohol induced a dose-dependent decrease of lipid order which was measured by steady-state fluorescence anisotropy using trimethylammonium-diphenylhexatriene and propionyl-diphenylhexatriene as fluorescent probes. Benzyl alcohol induced a 2-fold increase in basal cAMP content, likely as a consequence of increased prostaglandin synthesis since this effect was abolished by indomethacin. The effect of benzyl alcohol on stimulated cAMP synthesis depended on the nature of the ligand: 10 mM benzyl alcohol increased significantly the stimulatory effect of prostaglandin E2, glucagon and forskolin but not of vasopressin. At higher concentrations (40 mM), benzyl alcohol did not affect significantly the glucagon-stimulated cAMP content, while it inhibited significantly the prostaglandin E2-, forskolin- and vasopressin-stimulated cAMP synthesis. The 40 mM benzyl alcohol-induced inhibition was reversed by 1 mM Mn2+, which is known to block the inhibitory GTP-binding protein Ni. These results suggest that: (i) the various components of the adenylate cyclase-cAMP system and their coupling are affected differently by changes in membrane fluidity, which might reflect differences in their lipid environment, (ii) changes in membrane fluidity can modulate responses of renal tubular cells to hormones, and thus tubular functions.
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PMID:Benzyl alcohol increases membrane fluidity and modulates cyclic AMP synthesis in intact renal epithelial cells. 282 Apr 91

Previous studies have indicated the existence of two separate pools of phosphoinositides in WRK-1 cells; one is labile and hormone-sensitive with respect to turnover, while the other is stable. Hormonal stimulation results in a rapid increase in 32Pi incorporation into the sensitive pool, while in the absence of hormone, incorporation of 32Pi into this pool is slow. Results are quite different when [3H]inositol is the precursor utilized. Incorporation of [3H]inositol into hormone-sensitive phosphoinositides is not stimulated in the presence of hormone, suggesting entry of this exogenous precursor into the cycle by a route other than the resynthetic phase of the cycle. Furthermore, failure of hormone to induce loss of [3H]phosphoinositide in pulse-chase experiments in the absence of lithium suggests reutilization of the [3H]inositol moiety generated by phosphodiesteratic cleavage of hormone-sensitive phosphoinositide. Time course studies indicate that the relative rates of incorporation of [3H]inositol into sensitive and insensitive phosphoinositide remain constant from 2 to 24 h. Several factors are capable of increasing [3H]inositol incorporation into hormone-insensitive phosphoinositide including vasopressin, calcium ionophores, and manganese. On the other hand, vasopressin treatment appears to decrease incorporation of [3H]inositol into the hormone-sensitive pool, probably by shifting the equilibrium between phosphoinositides and inositol phosphates, since the decrease in radioactivity observed in the phosphoinositides is equaled by the increase observed in that in the inositol phosphates.
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PMID:Inositol metabolism in WRK-1 cells. Relationship of hormone-sensitive to -insensitive pools of phosphoinositides. 282 Sep 60


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