Does in vitro activation of postsynaptic α2-adrenoceptor utilize intracellular Ca2+ for contraction in dog saphenous vein?

1989 ◽  
Vol 67 (9) ◽  
pp. 1086-1091 ◽  
Author(s):  
Y. Y. Guan ◽  
C. Y. Kwan ◽  
E. E. Daniel
Keyword(s):  
Saphenous Vein ◽  
Krebs Solution ◽  
Free Medium ◽  
High Concentration ◽  
Dog Saphenous Vein ◽  
Ph Buffering ◽  
Intracellular Ca ◽  
Muscle Calcium ◽  
Subsequent Addition

Dog saphenous vein spiral strips were employed to determine whether an intracellular source of Ca2+ is used for contraction upon activation of the α2-adrenoceptor by B-HT 920 in Ca2+-free Krebs solution containing 50 μM EGTA. The studies were carried out in parallel with the activation of the α1-adrenoceptor by phenylephrine (Phe) under the condition that B-HT 920 (10−5 M) and Phe (2 × 10−6 M) gave rise to a similar level of responses in Ca2+-containing Krebs solution. A similar level of responses to these agonists at equieffective concentrations in Ca2+-free medium were also observed. Such responses to Phe and B-HT 920 were inhibited by 10−7 M rauwolscine and 10−7 M prazosin, respectively, and were not affected by 10−7 M nifedipine or 5 mM Mn2+. The responses to B-HT 920 (10−5 M) and submaximal concentration of Phe (2 × 10−6 M) in Ca2+-free medium were additive. However, if the vascular strips were first contracted maximally with 10−4 M Phe in Ca+2-free medium to deplete the intracellular Ca store, subsequent addition of B-HT 920 failed to induce additional response. Our results strongly suggest that activation of α2-adrenoceptor in dog saphenous vein in Ca2+-free medium indeed utilizes intracellular Ca2+ for contraction. We also found that the failure of earlier studies to demonstrate the contractile effects of B-HT 920 in dog saphenous vein was due to experimental artifacts derived from the use of high concentration of EGTA and artificial pH-buffering reagent.Key words: adrenoceptor, saphenous vein, vascular muscle, calcium.

Inhibitory effects of tetramethyl and tetraethyl derivatives of pyrazine on dog saphenous vein

1991 ◽  
Vol 69 (8) ◽  
pp. 1184-1189 ◽  
Author(s):  
Z. L. Wang ◽  
C. Y. Kwan ◽  
A. Ohta ◽  
M. C. Chen
Keyword(s):  
Smooth Muscle ◽  
Saphenous Vein ◽  
Inhibitory Effect ◽  
Induced Responses ◽  
Adrenergic Agonist ◽  
Dog Saphenous Vein ◽  
Contractile Responses ◽  
Intracellular Ca ◽  
Prostaglandin F ◽  
Muscle Calcium

The effects of two structurally similar pyrazine derivatives, tetramethylpyrazine (TMP) and tetraethylpyrazine (TEP) on the contractile responses of dog saphenous vein to KCl (via membrane depolarization), phenylephrine (PHE, α1-adrenergic agonist), and B-HT 920 (α2-adrenergic agonist) were investigated. The relaxant or inhibitory effect of TMP and TEP was most potent on KCl-induced responses and least potent on PHE-induced responses. Their effect on KCl-induced responses was more prominent at 30 mM KCl than at 100 mM KCl. In Ca2+-free medium, PHE and B-HT 920 elicited transient responses, which were also markedly and reversibly inhibited by TMP and TEP. Similar results were also obtained when prostaglandin F2α was used as an agonist. In all four types of contractile responses involving different receptors, the inhibitory effect of TEP was consistently more potent than that of TMP. We conclude that both TMP and TEP behave as a nonselective smooth muscle relaxant having similar and multiple actions including their general interference with the processes involving both Ca2+ entry and intracellular Ca2+ release.Key words: vascular smooth muscle, calcium channels, tetramethylpyrazine, tetraethylpyrazine, α-adrenoceptors, saphenous vein.

Evidence against the role of α1-adrenoceptor reserve in buffering the inhibitory effect of nifedipine on the contractility of canine vascular smooth muscle

1990 ◽  
Vol 68 (10) ◽  
pp. 1346-1350 ◽  
Author(s):  
Yong-Yuan Guan ◽  
Chiu-Yin Kwan ◽  
Edwin E. Daniel
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Saphenous Vein ◽  
Mesenteric Artery ◽  
Inhibitory Effect ◽  
Contractile Responses ◽  
Intracellular Ca ◽  
Adrenoceptor Agonists ◽  
The Difference ◽  
Muscle Calcium

The relationship between the postsynaptic α1-adrenoceptor reserve and the sensitivity of vasoconstriction induced by α-adrenoceptor agonists to the dihydropyridine Ca2+ entry blocker nifedipine was investigated in isolated muscle strips of dog mesenteric artery (DMA) and saphenous vein (DSV). The amplitudes of the contractile responses of DMA induced by phenylephrine were the same as those in DSV in the presence and in the absence of extracellular Ca2+. The use of 3 × 10−9 M phenoxybenzamine to irreversibly block the α1-adrenoceptors revealed a marked difference in the size of the α1-adrenoceptor reserve between DMA (40%) and DSV (7%). In spite of a larger receptor reserve, the contractile responses induced by phenylephrine in DMA were more sensitive to nifedipine compared with those in DSV. These results suggest that the postsynaptic α1-adrenoceptor reserve in vascular smooth muscle, at least in DMA and DSV, does not play an important role in buffering the inhibitory effect of nifedipine on the contractile response to a full agonist of α1-adrenoceptors. Other factors, such as the difference in the membrane depolarizing effect, the ability to utilize intracellular Ca2+ for contraction, and the possible existence of α1-adrenoceptor subtypes, may contribute to the different inhibitory effects of nifedipine on these blood vessels.Key words: adrenoceptors, nifedipine, smooth muscle, calcium, saphenous vein, mesenteric artery.

Relationship between dog saphenous vein reactivity and Na content

1988 ◽  
Vol 255 (4) ◽  
pp. H860-H865
Author(s):  
V. Berczi ◽  
G. Simon
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Saphenous Vein ◽  
Dna Content ◽  
Mode Of Action ◽  
Venous Blood ◽  
Dog Saphenous Vein ◽  
Wide Range ◽  
Venous Wall ◽  
Stimulation Of

The physiological significance of the wide range of spontaneous variation in the total Na content of the dog saphenous vein (SV) was investigated. The SV of pentobarbital-anesthetized male mongrel dogs was perfused in vitro with the dogs' own venous blood, and its reactivity to acetylcholine (ACh) and norepinephrine (NE) was measured. The contralateral SV was removed for measurements of total and intracellular (Li exchange at 4 degrees C) Na and K content, DNA content, and muscle width. Reactivity to ACh correlated directly with total and extracellular SV Na content, and reactivity to NE correlated directly with total and intracellular K content. Reactivity to NE was unrelated to ACh reactivity, plasma NE concentration, or venous wall DNA content or muscle width. ACh-mediated venoconstriction was approximately 10 times more sensitive to inhibition by amiloride, an inhibitor of Na-entry pathways, than NE-mediated venoconstriction. The finding that extracellular Na content is a marker of reactivity to ACh is compatible with experimental evidence that the mode of action of ACh may be the stimulation of Na influx. The positive correlation between the K content and reactivity of veins to NE suggests that there is a link between intracellular K content and the release of Ca from the sarcoplasmic reticulum in response to NE.

Mepivacaine-induced contraction is attenuated by endothelial nitric oxide release in isolated rat aorta

2012 ◽  
Vol 90 (7) ◽  
pp. 863-872 ◽  
Author(s):  
Hui-Jin Sung ◽  
Mun-Jeoung Choi ◽  
Seong-Ho Ok ◽  
Soo Hee Lee ◽  
Il Jeong Hwang ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Methylene Blue ◽  
Calcium Influx ◽  
Guanosine Monophosphate ◽  
Krebs Solution ◽  
High Concentration ◽  
Response Curves ◽  
Endothelial Nitric Oxide ◽  
Isolated Rat

Mepivacaine is an aminoamide-linked local anesthetic with an intermediate duration that intrinsically produces vasoconstriction both in vivo and in vitro. The aims of this in-vitro study were to examine the direct effect of mepivacaine in isolated rat aortic rings and to determine the associated cellular mechanism with a particular focus on endothelium-derived vasodilators, which modulate vascular tone. In the aortic rings with or without endothelium, cumulative mepivacaine concentration–response curves were generated in the presence or absence of the following antagonists: Nω-nitro-l-arginine methyl ester [l-NAME], indomethacin, fluconazole, methylene blue, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one [ODQ], verapamil, and calcium-free Krebs solution. Mepivacaine produced vasoconstriction at low concentrations (1 × 10−3 and 3 × 10−3 mol/L) followed by vasodilation at a high concentration (1 × 10−2 mol/L). The mepivacaine-induced contraction was higher in endothelium-denuded aortae than in endothelium-intact aortae. Pretreatment with l-NAME, ODQ, and methylene blue enhanced mepivacaine-induced contraction in the endothelium-intact rings, whereas fluconazole had no effect. Indomethacin slightly attenuated mepivacaine-induced contraction, whereas verapamil and calcium-free Krebs solution more strongly attenuated this contraction. The vasoconstriction induced by mepivacaine is attenuated mainly by the endothelial nitric oxide – cyclic guanosine monophosphate pathway. In addition, mepivacaine-induced contraction involves cyclooxygenase pathway activation and extracellular calcium influx via voltage-operated calcium channels.

H2O2: a mediator of esophagitis-induced damage to calcium-release mechanisms in cat lower esophageal sphincter

2005 ◽  
Vol 288 (6) ◽  
pp. G1170-G1178 ◽  
Author(s):  
Weibiao Cao ◽  
Karen M. Harnett ◽  
Ling Cheng ◽  
Michael T. Kirber ◽  
Jose Behar ◽  
...  
Keyword(s):  
Atpase Activity ◽  
Lower Esophageal Sphincter ◽  
Calcium Release ◽  
Circular Muscle ◽  
Activity Measurement ◽  
Free Medium ◽  
High Concentration ◽  
Normal Cells ◽  
Intracellular Ca ◽  
Esophageal Sphincter

We previously reported that induction of acute experimental esophagitis by repeated perfusion of HCl may affect release of intracellular Ca2+ stores. We therefore measured cytosolic Ca2+ in response to a maximally effective dose of ACh in fura 2-AM-loaded lower esophageal sphincter (LES) circular muscle cells and examined the contribution of H2O2 to the reduction in Ca2+ signal. In normal cells, the ACh-induced Ca2+ increase was the same in normal-Ca2+ and Ca2+-free medium and was abolished by the phosphatidylinositol 4,5-bisphosphate-specific phospholipase C inhibitor U-73122, confirming that the initial ACh-induced contraction depends on Ca2+ release from intracellular stores through production of inositol trisphosphate. In LES cells, the ACh-induced Ca2+ increase in normal-Ca2+ medium was significantly lower in esophagitis than in normal cells and was further reduced (∼70%) when the cells were incubated in Ca2+-free medium. This reduction was partially reversed by the H2O2 scavenger catalase. H2O2 measurements in LES circular muscle showed significantly higher levels in esophagitis than in normal cells. When normal LES cells were incubated with H2O2, the ACh-induced Ca2+ increase was significantly reduced in normal-Ca2+ and Ca2+-free medium and was similar to that observed in animals with esophagitis. The initial ACh-induced contraction was also reduced in normal cells incubated with H2O2. H2O2, when applied to cells at sufficiently high concentration, produced a visible and prolonged Ca2+ signal in normal cells. H2O2-induced cell contraction was also sensitive to depletion of stores by thapsigargin (TG); conversely, H2O2 reduced TG-induced contraction, suggesting that TG and H2O2 may operate through similar mechanisms. Ca2+-ATPase activity measurement indicates that H2O2 and TG reduced Ca2+-ATPase activity, confirming similarity of mechanism of action. We conclude that H2O2 may be at least partly responsible for impairment of Ca2+ release in acute experimental esophagitis by inhibiting Ca2+ uptake and refilling Ca2+ stores.

Effects of prostaglandins and endoperoxide analogs on canine saphenous vein

1977 ◽  
Vol 233 (3) ◽  
pp. H361-H368
Author(s):  
M. R. Goldberg ◽  
V. S. Hebert ◽  
P. J. Kadowitz
Keyword(s):  
Saphenous Vein ◽  
High Concentration ◽  
Venous Tone ◽  
Canine Saphenous Vein ◽  
Saphenous Veins ◽  
Venous Function ◽  
Vitro Model ◽  
Induced Changes

Contractile effects of prostaglandins (PGs) have not been widely studied in the canine saphenous vein, as in vitro model for venous function. We studied responses to two PG endoperoxide analogs (PGEA) and to monoenoic and bisenoic PGs of the A, B, E, and F series in helical strips of canine saphenous veins. Isometric changes in force were measured. All agents elicited marked contractions. PGEA were several orders of magnitude more potent than either primary PGs or other venoconstrictors, including norepinephrine. E- and A-types PG had unusual concentration and contraction at high concentration. B-types PG evoked a biphasic contractile response. Bisenoic PGs tended to be more potent than monoenoic PGs of the same type. These results show that canine saphenous veins are highly responsive to PGs and PGEA. These data suggest that these substances could influence venous tone in vivo. However, PG-induced changes in venous tone would depend on which PG or intermediate was present, on PG concentration, and on the prior state of venous tone.

Inhibitory effect of endothelin on renin release in vitro

1989 ◽  
Vol 257 (6) ◽  
pp. E833-E838 ◽  
Author(s):  
M. Takagi ◽  
H. Tsukada ◽  
H. Matsuoka ◽  
S. Yagi
Keyword(s):  
Present Report ◽  
Inhibitory Effect ◽  
Renin Release ◽  
High Concentration ◽  
Cellular Mechanisms ◽  
Cortical Cells ◽  
Superfusion System ◽  
Ca Antagonist ◽  
Intracellular Ca

We previously reported that endothelin inhibits renin release in a dynamic superfusion system of collagenase-dispersed rat renal cortical cells. In the present report we investigated cellular mechanisms by which endothelin inhibits renin release from juxtaglomerular (JG) cells. In a superfusion system of dispersed rat renal cortical cells, 10(-10) M endothelin inhibited renin release stimulated by 5 x 10(-8) M isoproterenol or 5 x 10(-5) M 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8, a putative intracellular Ca antagonist). Endothelin showed a slight but significant inhibitory effect on renin release stimulated by isoproterenol or TMB-8 even in the absence of extracellular Ca. Endothelin also inhibited renin release in the presence of 10(-4) M nicardipine. In a superfusion system of renal cortical slices, both 10(-8) M endothelin and a high concentration (60 mM) of K inhibited renin release, and 10(-6) M nicardipine attenuated the inhibition of renin release by high K but did not affect the inhibition by endothelin. These results suggest that endothelin inhibits renin release from JG cells not only by the promotion of Ca influx into the cells through dihydropyridine-insensitive Ca channels but also by other mechanism(s) independent of extracellular Ca.

Induction of LTD in the Dentate Gyrus In Vitro Is NMDA Receptor Independent, but Dependent on Ca2+ Influx via Low-Voltage–Activated Ca2+ Channels and Release of Ca2+ From Intracellular Stores

1997 ◽  
Vol 77 (2) ◽  
pp. 812-825 ◽  
Author(s):  
Yue Wang ◽  
Michael J. Rowan ◽  
Roger Anwyl
Keyword(s):  
Nmda Receptor ◽  
Dentate Gyrus ◽  
Low Voltage ◽  
Ryanodine Receptors ◽  
Long Term Potentiation ◽  
Ruthenium Red ◽  
High Concentration ◽  
Intracellular Ca

Wang, Yue, Michael J. Rowan, and Roger Anwyl. Induction of LTD in the dentate gyrus in vitro is NMDA receptor independent, but dependent on Ca2+ influx via low-voltage-activated Ca2+ channels and release of Ca2+ from intracellular stores. J. Neurophysiol. 77: 812–825, 1997. The mechanisms of the induction of long-term depression (LTD) of field excitatory postsynaptic potentials (EPSPs) and whole cell patch-clamped excitatory postsynaptic currents (EPSCs) were studied in the dentate gyrus of the rat hippocampus. LTD of field EPSPs measuring 40% of control at 30 min poststimulation was induced by low-frequency stimulation consisting of 900 pulses at 1 Hz. LTD of EPSCs measuring 37% of control was induced by a pairing procedure consisting of 60 pulses at 1 Hz applied under voltage clamp at a holding potential of −40 mV. The induction of LTD of field EPSPs was dependent on an influx of extracellular calcium, being reduced in a low-Ca2+ (0.8 mM) medium. However, substantial LTD (26%) was still induced in such a medium, demonstrating the relatively low sensitivity of LTD induction to the level of extracellular Ca2+. A high concentration of the N-methyl-d-aspartate receptor antagonist d(−)-2-amino-5-phosphonopentanoic acid (d-AP5) (100 μM) did not significantly inhibit the induction of LTD of EPSCs evoked by the intracellular pairing procedure. d-AP5 partially reduced the magnitude of LTD of field EPSPs, but substantial LTD was still induced in the presence of AP5. The induction of LTD was strongly inhibited by Ni2+ (50 μM) but not by nifedipine (10 μM), indicating that Ca2+ influx via T-type, but not L-type, Ca2+ channels is required for the induction of LTD. The induction of LTD was strongly inhibited by thapsigargin, an agent known to deplete intracellular Ca2+ stores. The induction of LTD, but not long-term potentiation (LTP), was also strongly inhibited by ruthenium red, an agent known to block the ryanodine receptors located on intracellular Ca2+ stores. These results demonstrate that Ca2+ release from intracellular Ca2+ stores is required for the induction of LTD, but not LTP. The results of the present experiments suggest that the induction of LTD involves the entry of Ca2+ via low-voltage–activated voltage-gated Ca2+ channels followed by release of Ca2+ from intracellular ryanodine-receptor-sensitive Ca2+ stores.

IN VITRO UPTAKE OF TRITIATED OESTRADIOL BY THE ANTERIOR HYPOTHALAMUS AND HYPOPHYSIS OF THE RAT

1970 ◽  
Vol 64 (4) ◽  
pp. 687-695 ◽  
Author(s):  
Junzo Kato
Keyword(s):  
Incubation Medium ◽  
Posterior Hypothalamus ◽  
Anterior Hypothalamus ◽  
Ovariectomized Rats ◽  
Free Medium ◽  
Cortex Cerebri ◽  
Anterior Hypophysis ◽  
In Vitro Uptake

ABSTRACT The anterior, middle, and posterior hypothalamus, the cortex cerebri, the anterior hypophysis as well as the diaphragm of adult ovariectomized rats were incubated in vitro with tritiated 17β-oestradiol. The uptake of tritiated oestradiol was differentially distributed intracerebrally with higher accumulation in the anterior hypothalamus and the hypophysis. Lowering the temperature of the incubation medium caused a reduction in the uptake of radioactivity by the anterior hypothalamus as compared to that found in other brain tissues. Tritiated oestradiol taken up in vitro by the anterior hypothalamus and the hypophysis tended to be retained after further incubation in a steroid-free medium. The addition of non-radioactive 17β-oestradiol to the medium inhibited the uptake of tritiated oestradiol by these tissues. Moreover, pretreatment with non-radioactive 17β-oestradiol in vivo prevented the preferential accumulation of tritiated oestradiol in vitro in the anterior hypothalamus and the hypophysis. These results indicate that oestradiol is preferentially taken up in vitro by the anterior hypothalamus and the hypophysis of the rat.

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