Receptors In Vascular Smooth Muscle Research Articles

Pharmacology of the human ovarian vein: responses to putative neurotransmitters and endothelin-1.

An investigation of excitatory vascular responses in the human ovarian vein, a blood vessel normally exposed to high concentrations of ovarian steroid hormones and capable of adaptation to circulatory changes associated with reproductive life. Pharmacological responses of surgical specimens of human ovarian vein to electrical field stimulation of sympathetic nerves, noradrenaline, alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-MeATP), endothelin-1 (ET-1), and 5-hydroxytryptamine (5-HT) were studied. Comparisons were made between in vitro pharmacological responses and the diagnostic category, age, smoking status, reproductive history and hormonal status of patients. Research laboratory. Maximal contractile responses in longitudinal preparations, expressed as a percentage of the response to potassium chloride 125 mmol l-1, were 28% (SE 7.2) to electrical field stimulation and 107% (SE 15.1) to noradrenaline. In ring preparations, maximal responses to various agents were: noradrenaline 93% (SE 10.2); 5-HT 79% (SE 8.0); alpha,beta-MeATP 48% (SE 8.4); and ET-1 87% (SE 10.1). pD2(-log EC50) values for noradrenaline were 5.82 (SE 0.21) in longitudinal preparations and 5.65 (SE 0.10) in ring preparations; for ET-1 in ring preparations these values were 7.88 (SE 0.74). Responses to sympathetic nerve stimulation were attenuated by the adrenoceptor antagonist phentolamine; any residual responses were blocked by desensitisation of P2-purinoceptors with alpha,beta-MeATP or the addition of suramin, indicating that noradrenaline and adenosine 5'-triphosphate may be co-transmitters in these nerves. pD2 values for 5-HT were 5.97 (SE 0.12) in specimens from unsterilised patients (n = 19) compared with 5.20 (SE 0.24) in specimens from those who had previously undergone sterilisation (n = 6) (P < 0.05). No other relation between clinical characteristics and pharmacological responses were detected and, in particular, there were no apparent changes associated with ageing or hormonal status. Three main conclusions may be drawn from this study: (1) adenosine 5'-triphosphate is a co-transmitter in sympathetic nerves in the human ovarian vein; (2) tubal sterilisation affects vascular responsiveness to 5-HT; and (3) ovarian steroid hormones are likely to influence sympathetic vascular control via effects on catecholamine and adenosine 5'-triphosphate synthesis, storage, release, degradation or re-uptake, rather than via effects on vascular smooth muscle receptors.

Human endothelin ET A receptor antisense oligodeoxynucleotides inhibit endothelin-1 evoked vasoconstriction

Antisense oligodeoxynucleotides to endothelin ET A receptor mRNA were used to characterize vascular smooth muscle receptors. The concentration-response curve showed a significant attenuation of endothelin-1-induced contraction in circular segments of the human superficial temporal artery. Endothelin ET B receptor antisense or mismatch oligodeoxynucleotides showed no alteration of the endothelin-1-induced contraction. Complementary experiments with the selective endothelin ET A receptor antagonist FR139317 demonstrated a shift of the concentration-response curve to the right in a competitive manner (pA 2 = 6.93). The specific method of using the receptor antisense oligodeoxynucleotides approach revealed the presence of endothelin ET A receptors mediating contraction in the human superficial temporal artery.

Nonreceptor-mediated intestinal vasoconstriction in portal hypertensive rats.

Previous studies have demonstrated that receptor-mediated vasoconstriction is impaired in chronic portal hypertension (PH). Furthermore, it has been suggested that altered vasoconstrictor effectiveness in chronic PH is due to a defect in the intracellular events associated with smooth muscle activation and not to impaired coupling of vasoconstrictors with vascular smooth muscle receptors. The present study was designed to determine whether nonreceptor-mediated vasoconstrictor responses are impaired in the PH intestinal microcirculation. Specifically, we examined the effects of aluminum fluoride-induced activation of G proteins, KCl-induced depolarization, caffeine-induced release of intracellular Ca2+, and l-indolactam-induced activation of protein kinase C on the intestinal microcirculation of normal (Norm, n = 39) and PH (n = 42) rats. The small intestine was prepared for microcirculatory studies and transferred to a video microscope. First-order arteriolar (1A) diameter and red cell velocity were measured on-line. Blood flow was calculated from the product of velocity and microvessel cross-sectional area. After a control period, the microvasculature was exposed to a solution containing aluminum chloride plus sodium fluoride, potassium chloride, caffeine, or l-indolactam. Maximal decreases in arteriolar diameter produced by aluminum fluoride, KCl, caffeine, and l-indolactam were significantly greater in Norm rats when compared with PH rats. Changes in arteriolar blood flow were also larger in Norm than in PH rats. The results of the present study provide the first direct evidence of an impaired response to second-messenger activation in the PH circulation.

Mechanisms of augmented vascular responses to histamine in atherosclerotic rabbit common carotid arteries

The vascular responsiveness to histamine, 2-pyridylethylamine and dimaprit was investigated in isolated and perfused atherosclerotic rabbit common carotid arteries enclosed by a hollow silastic collar. The constrictor effects of histamine were significantly enhanced in atherosclerotic arteries, although those of 2-pyridylethylamine were not changed. The dilator effects of histamine and dimaprit, which were completely inhibited after pretreatment with cimetidine, were not influenced by removal of the endothelium but significantly depressed in atherosclerotic arteries. The dose-response curves for histamine in the control group pretreated with cimetidine were shifted to the left and responses reached almost the same level as those of the atherosclerotic group. From these results, it is concluded that histamine-induced vasoconstrictions are enhanced in atherosclerotic arteries, and that the mechanism of the hyperreactivity to histamine might be an attenuation of the vasodilatations mediated via histamine H 2 receptors in vascular smooth muscle.

Micromolar calcium decreases affinity of inositol trisphosphate receptor in vascular smooth muscle.

The mechanism by which Ca2+ inhibits InsP3-induced Ca2+ release from sarcoplasmic reticulum of vascular smooth muscle was investigated. InsP3 binding to sarcoplasmic-reticulum vesicles from dog aortic smooth muscle was inhibited by 51 +/- 6% by 2 microM Ca2+ in the presence of 10 nM [3H]InsP3. Scatchard analysis indicated the presence of two InsP3-binding sites in the absence of Ca2+ (Kd = 2.5 +/- 0.9 and 49 +/- 8 nM InsP3), though the low-affinity site was more prevalent (representing 92 +/- 3% of the total number of binding sites). Ca2+ (2 microM) did not alter InsP3 binding to the high-affinity site (P > 0.05), but increased the Kd of the low-affinity site 3-fold (Kd = 155 +/- 4 nM InsP3; P < 0.001). The possibility that the apparent decrease in InsP3 affinity was caused by Ca(2+)-dependent activation of an endogenous phospholipase C could be excluded, because the Ca(2+)-dependent inhibition of InsP3 binding was completely reversible and insensitive to an inhibitor of phospholipase C. Moreover, Ca2+ did not inhibit InsP3 binding to InsP3 receptor partially purified by heparin-Sepharose chromatography, though another fraction (devoid of InsP3 receptor) restored Ca(2+)-sensitivity of the partially purified InsP3 receptor. Thus Ca2+ binding to a Ca(2+)-sensitizing factor associated with the InsP3 receptor decreases the affinity of the receptor complex for InsP3. This Ca(2+)-sensitizing factor may provide a negative-feedback mechanism for regulating the rise in cytosolic Ca2+ concentration in vascular smooth muscle after hormone activation of the phosphoinositide cascade.

Expression of 11β-hydroxysteroid dehydrogenase mRNA in rat vascular smooth muscle cells

The enzyme 11β-hydroxysteroid dehydrogenase (11-HSD) converts corticosterone to the inactive 11-dehydrocorticosterone in the rat. The bioactivity of 11-HSD, expressed as the percentage conversion of 3H-corticosterone to 3H-11-dehydrocorticosterone, was 13.7±0.4% in rat vascular smooth muscle cells (rVSMC). Cells treated with 100 nM dexamethasone (Dex) showed a 1.4-fold (p<0.05) increase in 11-HSD activity. Insulin (100 μM) decreased 11-HSD activity by 0.8-fold (p<0.05). Expression of 11-HSD mRNA was also confirmed in rVSMC by Northern blot analysis. Dexamethasone increased and insulin decreased the levels of 11-HSD mRNA in parallel with the increase in bioactivity. Vascular smooth muscle cells express 11-HSD activity; the access of corticosterone to vascular smooth muscle receptors may be modulated by the enzyme.

Ontogeny of angiotensin II vascular smooth muscle receptors in ovine fetal aorta and placental and uterine arteries

Our purpose was to determine if differences in angiotensin II vascular smooth muscle receptor binding account for the attenuated fetal placental and systemic responses to infused angiotensin II relative to maternal responses and for the differences between umbilical and fetal systemic responses. Using plasma membranes prepared from the medial layer of fetal aorta, fetal placental artery, and maternal uterine artery obtained between 107 and 134 days of ovine gestation (n = 17), we measured and compared angiotensin II receptor binding density (in femtomoles per milligram of protein) and affinity (in nanomoles per liter) in radioligand binding studies with iodine 125-angiotensin II. Maternal and fetal plasma angiotensin II were also compared. A single class of high-affinity receptor was identified in all arteries. Although the binding density was similar at < 100 and > 130 days for fetal aorta (388 +/- 87 [SE] vs 262 +/- 56), placental artery (319 +/- 95 vs 235 +/- 54), and uterine artery (46 +/- 6 vs 50 +/- 13), values for fetal arteries exceeded those for uterine arteries (p < or = 0.018) in spite of higher fetal plasma angiotensin II (74 +/- 18 vs 30 +/- 8 pg/ml, p < 0.01). Affinity did not differ between arteries and, except for fetal aorta (1.4 +/- 0.2 vs 2.1 +/- 0.4, r = 0.49, p = 0.045), was unchanged during late gestation. Differences between fetal and maternal responses and fetal placental and systemic responses to infused angiotensin II in sheep do not reflect alterations in total angiotensin II vascular smooth muscle receptor binding density or affinity.

Identification of a specific receptor for interleukin-1 in vascular smooth muscle cells: regulation by interleukin-1 and interleukin-6

A flourescently labeled ligand was utilized to establish the existence of an interleukin-1 (IL-1) receptor in vascular smooth muscle. The binding of the phycoerythrin-labeled IL-1β to the murine T cell line, EL-4, was examined as a positive control. The phycoerythrin-labeled IL-1β identified a specific IL-1 receptor in the EL-4 cells. Vascular smooth muscle cells were also positively stained by the fluorescent ligand. The binding of phycoerythrin-labeled IL-1β to these cells was saturable and reversed by 100-fold excess unlabeled IL-1β. Incubation of the vascular smooth muscle cells positively with IL-gb (25 ng/ml) or IL-6 (250 ng/ml) for 18 h increased and decreased, respectively, the percentage of cells positively stained by phycoerythrin-labeled IL-1β which suggest these cytokines regulate IL-1 receptor expression in these cells. These data indicate a specific receptor for IL-1 exists in vascular smooth muscle cells.

Functionally Distinct Endothelin B Receptors in Vascular Endothelium and Smooth Muscle

IRL 1620 {Suc-[Glu 9,Ala 11,15]-ET-1 (8-21)} (0.1 nM - 1μM), a novel ET B-selective endothelin (ET) agonist, produced endothelium-dependent relaxations in precontracted rabbit mesenteric artery (2 nM, EC 50) and endothelium-independent contractions in porcine coronary artery (18 nM, EC 50). ET-3 (0.1 nM-10 nM) produced qualitatively similar responses in the two tissues. The maximal contractions induced by IRL 1620 or ET-3 were substantially smaller (<20%) than that produced by ET-1. BQ-123 (1 μM), an ET A receptor antagonist, inhibited responses to ET-1 without affecting IRL 1620- or ET-3-induced responses in either tissue. Thus functionally distinct ET B receptors mediating vasodilator and vasoconstrictor effects are located on the vascular endothelium and smooth muscle, respectively. The overall effect of ET B receptor activation on vascular tone is tissue-specific and presumably reflects differing receptor distribution at the two sites.

The F 2-isoprostane, 8-epi-prostaglandin F2 α, a potent agonist of the vascular thromboxane/endoperoxide receptor, is a platelet thromboxane/endoperoxide receptor antagonist

F 2-isoprostanes are a recently discovered series of prostaglandin (PG)F 2-like compounds that are produced in vivo in humans by nonenzymatic free radical catalyzed peroxidation of arachidonic acid. One of the compounds that can be produced in abundance by this mechanism is 8-epi- PGF 2 α . 8-epi- PGF 2 α is a potent vasoconstrictor in the rat, an effect that has been shown to be mediated via interaction with vascular thromboxane (TxA 2)/ endoperoxide (PGH 2) receptors. In an effort to further understand the biological properties of this prostanoid in relation to its ability to interact with TxA 2/PGH 2 receptors, we examined its effects on human and rat platelets. At concentrations of 10 −6 M and 10 −5 M, 8-epi- PGF 2 α induced only a shape change in human platelets and at higher concentrations (10 −4 M) induced reversible but not irreversible aggregation. Both the shape change and reversible aggregation were unaffected by indomethacin but were inhibited by the TxA 2/PGH 2 receptor antagonist SQ29548. Conversely, 8-epi- PGF 2 α inhibited platelet aggregation induced by the TxA 2/PGH 2 receptor agonists U46619 (10 −6 M) and IBOP (3.3×10 −7 M) with an IC 50 of 1.6 × 10 −6 M and 1.8 × 10 −6 M, respectively. 8- epi- PGF 2 α also inhibited platelet aggregation induced by arachidonic acid. Similarly, in rat platelets, 8-epi- PGF 2 α alone induced only modest reversible aggregation but completely inhibited U46619-induced aggregation. Thus, whereas 8-epi- PGF 2 α is a potent agonist of TxA 2/PGH 2 receptors in rat vascular smooth muscle, it acts primarily as an antagonist of TxA 2/PGH 2 receptors in both rat and human platelets. Therefore, vasoconstriction induced by 8-epi- PGF 2 α would not be expected to be accompanied by platelet aggregation in vivo . These observations sustain the controversy that different TxA 2/PGH 2 receptor subtypes may exist in platelets and vascular smooth muscle.

Demonstration of processing and recycling of biologically active V 1 vasopressin receptors in vascular smooth muscle

Demonstration of processing and recycling of biologically active V ₁ vasopressin receptors in vascular smooth muscle

Correction: Demonstration of Processing and Recycling of Biologically Active V1 Vasopressin Receptors in Vascular Smooth Muscle

Correction: Demonstration of Processing and Recycling of Biologically Active V1 Vasopressin Receptors in Vascular Smooth Muscle

Effect of blocking angiotensin II receptor subtype on rat sympathetic nerve function.

This study examined effects of nonpeptide angiotensin II (Ang II) receptor subtype antagonists on the interaction of sympathetic function and Ang II in pithed rats. Effects of spinal cord stimulation (0.5-4 Hz) and norepinephrine (0.3-3 micrograms/kg i.v.) on mean arterial pressure (recorded with a carotid arterial catheter), cardiac output (measured with an electromagnetic flowmeter and flow probe around the thoracic ascending aorta), total peripheral resistance, and heart rate were determined. The subtype 1-selective Ang II receptor antagonist losartan (previously known as DuP 753) at 10 mg/kg i.v. blocked the hemodynamic responses to Ang II at 1 microgram/kg i.v. It inhibited mean arterial pressure and total peripheral resistance responses but not cardiac output and heart rate responses to spinal cord stimulation. In contrast, it reduced mean arterial pressure and cardiac output responses but not total peripheral resistance and heart rate responses to intravenous norepinephrine. Given at 100 mg/kg i.v., the subtype 2-selective receptor antagonist PD123177 did not reduce hemodynamic responses to intravenous Ang II, spinal cord stimulation, and intravenous norepinephrine. These results suggest that endogenous Ang II facilitates the release of norepinephrine from sympathetic nerve terminals in the vasculature of pithed rats. Similar to the Ang II receptor in vascular smooth muscle, the prejunctional Ang II receptor in pithed rats appears to be of subtype 1.

Demonstration of processing and recycling of biologically active V1 vasopressin receptors in vascular smooth muscle.

The present study examines the binding and postbinding cellular processing and recycling of the V1 arginine vasopressin (AVP) receptor in cultured vascular smooth muscle cells (VSMCs). The surface binding of AVP to VSMCs was temperature dependent and reached equilibrium within 60 min at 4 degrees C. Displacement studies with unlabeled AVP or a specific V1 AVP antagonist revealed a single class of V1 receptors (Bmax, 1.99 pmol [corrected] per mg of protein; Kd, 2.15 nM). Incubation of VSMCs with unlabeled 10 nM AVP to promote receptor internalization resulted in a time- and temperature-dependent loss of AVP surface binding. At 37 degrees C, maximum loss of binding sites (65%) occurred within 20 min. Recovery of AVP binding occurred rapidly (t1/2, 15-20 min at room temperature) and was uninfluenced by inhibiting protein synthesis with cycloheximide. Pretreating VSMCs with chloroquine prevented AVP receptor recycling, indicating that the AVP-receptor complex requires endosomal processing. The biological competence of the recycled AVP receptor was shown by AVP-induced Ca2+ uptake. The results of these studies therefore indicate that, after surface binding, the AVP-receptor complex internalizes and dissociates in an endosomal compartment. It is demonstrated that in VSMCs biologically active V1 AVP receptors recycle back to the cell surface, thus attenuating the loss of AVP surface binding sites.

Angiotensin II vascular smooth-muscle receptors are not down-regulated in near-term pregnant sheep

Normal human and ovine pregnancies are associated with elevated plasma angiotensin II levels and refractoriness to the vasoconstrictor effects of infused angiotensin II, which is greater in the ovine uteroplacental vascular bed than in the systemic vasculature. It remains unclear whether this refractoriness reflects alterations in angiotensin II vascular smooth-muscle receptor density or affinity. We examined the angiotensin II vascular smooth-muscle receptor in nonpregnant (n = 12) and near-term pregnant (130 ± 3 days [mean ± SO], n = 1 0) sheep, comparing binding characteristics on plasma membranes prepared from the medial layer of aorta, mesenteric artery, and uterine artery. Plasma angiotensin II levels were increased threefold to fourfold (p < 0.001) in pregnant ewes. A single class of high-affinity angiotensin II vascular smooth-muscle receptor was identified in each type of artery. Receptor density was similar in nonpregnant and pregnant mesenteric artery (92 ± 21 vs 103 ± 40 fmol/mg protein, respectively), aorta (186 ± 29 vs 220 ± 46 fmol/mg protein), and uterine artery (59 ± 20 vs 77 ± 20 fmol/mg protein) tissue. Receptor affinity also was unchanged during pregnancy. Because changes in the density and affinity of the angiotensin II vascular smooth-muscle receptor were not obseNed in near-term pregnant ewes, the attenuated vasoconstrictor responses seen during pregnancy do not reflect receptor down-regulation or decreased affinity. (AM J OBSTET GYNECOL 1991;165:1641-8.)

Tissue- and species-specific differences in ligand binding to thromboxane A2 receptors

The ligand binding site of vascular smooth muscle (VSM) and platelet thromboxane A2 (TxA2) receptors was characterized in humans and rabbits using the TxA2 mimetic [125I]BOP. Vessel contraction and platelet aggregation studies demonstrated that unlabeled I-BOP and the prostaglandin H2 (PGH2) mimetic U-46619 were potent agonists in rabbit aortas, human saphenous veins, and washed human and rabbit platelets. [125I]BOP bound saturably to a single site on cultured vascular smooth muscle (VSM) cells from rabbit aortas and human saphenous veins with dissociation constants (Kd) of 392 +/- 8 (n = 5) and 390 +/- 120 pM (n = 6) and binding capacities (Bmax) of 5,322 +/- 200 and 2,017 +/- 322 sites/cell, respectively. [125I]BOP also bound saturably to one site on rabbit platelets (Kd = 415 +/- 15 pM, Bmax = 594 +/- 43 sites/platelet, n = 4) but, in agreement with previous studies, to two sites on human platelets (high-affinity Kd = 118 +/- 24 pM, Bmax = 121 +/- 33 sites/platelet; low-affinity Kd = 1.1 +/- 0.47 nM, Bmax 232 +/- 23 sites/platelet, n = 4). [125I]BOP was displaced from its binding site on rabbit and human VSM and platelets by stable TxA2/PGH2 analogues possessing either agonist or antagonist activity but not by other prostaglandins. The rank orders of the binding inhibition constants (IC50) for the TxA2/PGH2 analogues were compared among the four tissues and were highly correlated (r = 0.963) in VSM and platelets from rabbits but not humans (r = 0.699), suggesting that human VSM TxA2 receptors may be distinct from platelet TxA2 receptors. The IC50 rank order was also highly correlated (r = 0.935) between human and rabbit platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of angiotensin II antagonism on canine renal sympathetic nerve function.

The objective of this study was to examine effects of nonpeptide angiotensin II (Ang II) receptor antagonists on renal vasoconstrictor responses to renal nerve stimulation (RNS) and intrarenal injection of norepinephrine in pentobarbital-anesthetized dogs. The subtype 1-selective Ang II receptor antagonists, DuP 753 (2-n-butyl-4-chloro-5-(hydroxymethyl)-1-[(2'-(1H- tetrazol-5-yl)biphenyl-4-yl)methyl]imidazole, potassium salt) and EXP3174 (2-n-butyl-4-chloro-1-[(2'-(1H-tetrazol-5-yl) biphenyl-4-yl)methyl]imidazole-5-carboxylic acid) given intra-arterially to the kidney caused dose-dependent reductions of renal vasoconstrictor responses to RNS but not to norepinephrine. In contrast, the subtype 2-selective Ang II receptor specific ligand, PD 123177 (1-[(4-amino-3-methylphenyl)methyl]-5-(diphenylacetyl)-4,5,6,7- tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid), did not alter the renal vasoconstrictor responses to RNS, norepinephrine, and Ang II in doses of 10-100 micrograms/kg/min i.a. Captopril also reduced the renal vasoconstrictor responses to RNS but not to norepinephrine. However, saralasin did not alter the renal vasoconstrictor responses to RNS and norepinephrine, although it was as effective as DuP 753 and EXP3174 in blocking the renal vasoconstrictor response to Ang II. These results suggest that endogenous Ang II enhances renal adrenergic function at the prejunctional site in anesthetized dogs. Analogous to the Ang II receptor in vascular smooth muscle, the prejunctional Ang II receptor appears to be of subtype 1. Mechanisms accounting for the absence of the inhibition of Ang II-mediated renal adrenergic response by saralasin remain to be determined.

No change in alpha 1 adrenoceptors in canine femoral arteries after lumbar sympathectomy.

In the dog, alpha 1 adrenoceptors have been identified in the aorta, femoral mesenteric, and renal arteries. The concentration of alpha receptors may be regulated by hormones such as estrogen and progesterone and by drugs such as epinephrine. To assess whether sympathetic denervation, which is known to decrease norepinephrine output, might change the population of alpha 1 receptors in vascular smooth muscle, the femoral artery alpha 1 receptor population was examined 2 weeks after unilateral lumbar sympathectomy. [3H]Prazosin radioligand receptor assay analysis was used to measure the alpha 1 receptor populations. No statistical difference for dissociation constant and receptor density values between sympathectomy and nonsympathectomy femoral artery samples could be detected.

Intercellular communication through gap junctions: A potential role in pharmacomechanical coupling and syncytial tissue contraction in vascular smooth muscle isolated from the human corpus cavernosum

Kinetic and steady-state protocols were used to examine the effects of disruption of intercellular communication with heptanol, on contractile responses elicited by activation of the α 1-adrenergic receptor in human corporal vascular smooth muscle. For the steady-state studies, strips of corporal tissue from 19 patients were submaximally precontracted with phenylephrine (PE) and then relaxed by the cumulative addition of heptanol. Heptanol completely and reversibly relaxed all tissues studied in a concentration-dependent manner. The heptanol concentration response data were then computer fit to the general logistic equation to obtain pEC 50 (negative logarithm of the concentration that elicits one-half of the maximal effect) and slope factor values, with E max (maximal relaxation) set to 100%. The mean pEC 50 and slope factor values, respectively, were 2.86±0.04 and 1.86±0.17. Furthermore, kinetic studies on corporal tissues from a subset of the patient population (11 patients) revealed that preincubation of tissues with 2 mM heptanol caused a significant decrease in both the rate and magnitude of PE-induced contractions in all tissues studied, without affecting the rate constant for onset of contraction (k obs). The present results on intact tissue extend our previous observations on cultured corporal cells, and support the supposition that intercellular communication through gap junctions may play an important role in the initiation, maintenance and modulation of α 1-adrenergic contractions in human vascular smooth muscle.

Cloning of a cDNA encoding a non-isopeptide-selective subtype of the endothelin receptor

Endothelin-1 was initially identified as a 21-residue potent vasoconstrictor peptide produced by vascular endothelial cells, but was subsequently found to have many effects on both vascular and non-vascular tissues. The discovery of three isopeptides of the endothelin family, ET-1, ET-2 and ET-3, each possessing a diverse set of pharmacological activities of different potency, suggested the existence of several different endothelin receptor subtypes. Endothelins may elicit biological responses by various signal-transduction mechanisms, including the G protein-coupled activation of phospholipase C and the activation of voltage-dependent Ca2+ channels. Thus, different subtypes of the endothelin receptor may use different signal-transduction mechanisms. Here we report the cloning of a complementary DNA encoding one subtype belonging to the superfamily of G protein-coupled receptors. COS-7 cells transfected with the cDNA express specific and high-affinity binding sites for endothelins, responding to binding by the production of inositol phosphates and a transient increase in the concentration of intracellular free Ca2+. The three endothelin isopeptides are roughly equipotent in displacing 125I-labelled ET-1 binding and causing Ca2+ mobilization. A messenger RNA corresponding to the cDNA is detected in many rat tissues including the brain, kidney and lung but not in vascular smooth muscle cells. These results indicate that this cDNA encodes a 'nonselective' subtype of the receptor which is different from the vascular smooth muscle receptor.