北京鸭红细胞膜β肾上腺素受体放射配基结合测定法

本文以[³H]dihydroalprenolol([³H]DHA)为放射配基。对北京鸭红细胞(RBC)膜β受体进行了系统研究。结果表明,[³H]DHA与北京鸭RBC结合具有饱和性,肾上腺素能激动剂与[³H]DHA竞争结合的强弱顺序与它们的生物活性一致,提示结合有结构特异性和立体特异性,[³H]DHA与鸭RBC结合迅速、可逆。可见北京鸭RBC膜存在β受体,用于放射配基结合测定有取材方便,受体较丰富,膜蛋白得率高,[³H]DHA非特异结合低和易于保存等优点,可以代替火鸡RBC。     

四氢巴马汀等异喹啉生物碱对突触体及囊泡摄取[3H]多巴胺的影响

本文报道四氢巴马汀(THP)等异喹啉生物碱对[³H]DA摄取的作用。突触体对[³H]DA的亲和力常数Km为0.23μmol。最大摄取速率Vmax为1.2 nmol/g(5 min)。d-THP,1-SPD和1-THP对突触体摄取[³H]DA均有抑制作用,其IC₅₀分别为0.44,2.24和18.5μmol。d-THP的作用比1-THP约强20倍。nomifensine,苯丙胺和氟哌啶醇亦能有效地抑制[³H]DA摄取(IC₍₅₀₎分别为0.05,0.27和3.18μmol)。动力学研究表明,d-THP和nomifensine为DA摄取的竞争性抑制剂。用低渗溶液处理溶胀的方法研究药物对递质贮存的作用发现,与利血平相似,d-THP显著降低贮存囊泡[³H]DA含量并使囊泡与突触体[³H]DA含量之比明显减小。实验结果表明,THP等能抑制突触体摄取,并直接作用于贮存囊泡抑制[³H]DA贮存,因此具有利血平样排空作用。     

蝙蝠葛碱和粉防己碱对[3H]WEB 2086与体外牛脑前动脉平滑肌细胞结合的影响(英文)

用标记的血小板活化因子拮抗剂[³H]WEB 2086,在培养的牛脑前动脉平滑肌细胞上鉴定了血小板活化因子受体。结果表明在25℃时该细胞上存在两种与配基具有不同亲和力的受体结合位点,其中K_d-1=22.8±5.0 nmol·L^-1,K_d-2=186+20.5 nmol·L^-1;B_max-1=2.1±0.3 pmol/10⁴细胞,B_max-2=12.1±1-5 pmol/10⁶细胞。蝙蝠葛碱和粉防己碱均能抑制[³H]WEB2086与上述细胞的结合。     

新的高强度高选择性阿片μ受体激动剂[11C]-羟甲芬太尼的合成

羟甲芬太尼(I)是一个新的高强度高选择性阿片μ受体激动剂。本文用cis-A-N-[1-(2-羟基-2-苯乙基)-3-甲基-4-哌啶基]-苯胺(II)或cis-N-[1-(苯甲酰甲基)-3-甲基-4-哌啶基]-苯胺(III)作为前体合成了[¹¹C]-羟甲芬太尼,以便用正电子发射断层扫描(PET)来观察μ受体。通过水解cis-A-羟甲芬太尼(I)和cis-N-[1-(苯甲酰甲基)-3-甲基-4-哌啶]-N-苯基丙酰胺(cis-IV)的4-N-丙酰基分别获得II和III。溴乙烷的格氏试剂与回旋加速器产生的[¹¹C]-二氧化碳反应后继而直接加入邻苯二甲酸二酰氯和2,6-二叔丁基吡啶生成同位素标记中间体[¹¹C]-丙酰氯。[¹¹C]-丙酰氯与OH-前体(II)反应后再经HPLC分离纯化直接得[¹¹C]-羟甲芬太尼;[¹¹C]-丙酰氯与酮-前体(III)反应后,再用硼氢化钠甲醇溶液处理,然后进行HPLC分离纯化得[¹¹C]-羟甲芬太尼。两种方法均可获得ll.1～14.8GBq/μmol的特异性放射化学纯[¹¹C]-羟甲芬太尼。总共耗时为40～50min(EOB)。     

可乐定镇痛与中枢Ca2+的关系

用大鼠甩尾法和放射配基结合实验,探讨了可乐定镇痛与中枢Ca²⁺的关系。CaCl₂(1μmol/rat,icv)和EGTA(0.2μmol/rat,icv)分别拮抗和增强可乐定(1mg/kg,sc)的镇痛。戊脉安(0.1μmol/rat,icy)对可乐定(1 mg/kg,sc)镇痛无明显影响,但可部分翻转CaCl₂对可乐定镇痛的拮抗。CaCl₂(1×10^-3mol)对[³H]-可乐定结合无明显抑制。结果表明可乐定镇痛与脑室周围组织中Ca²⁺浓度变化密切相关,Ca²⁺至少部分需经对戊脉安敏感的钙通道进入细胞内方可拮抗可乐定镇痛。推沦:可乐定镇痛与神经元内Ca²⁺有关。     

氚标记强效镇痛剂N-[1-(β-羟基-β-苯乙基)-3-甲基-4-哌啶基]-N-丙酰苯胺的制备以及与阿片受体的结合试验

本文报道以N-[1-(对-溴苯甲酰甲基)-3-甲基-4-哌啶基]-N-丙酰苯胺(Ⅲ)为前体,以PdO/BaSO₄作催化剂,用氚气进行卤—氚置换,氚化还原羰基的反应。反应产物经硅胶纸层析纯化后,用甲基橙比色法定量测定,得到N-{1-[β-羟基-β-氚-β-(对-氚苯基)乙基]-3-甲基-4-哌啶基}-N-丙酰苯胺(Ⅳ,[³H]F-7302),其比放射性为59 Ci/mM,放化纯度为98%。[³H]F-7302与小鼠脑内阿片受体的特异性结合在浓度为4.5×10^-9M时达到饱和,解离常数Kd=1.25×10^-9M,最大结合量B_max=93.08×10¹²M/g蛋白,其特异性结合与非特异性结合比值达10～15。     

二氢埃托啡对大鼠脑阿片受体的结合特性

本文在大鼠脑匀浆P_2膜上,观察了二氢埃托啡(DHE)对[~3H]纳洛酮,[~3H]DPDPE和[~3H]埃托啡(预先用30nmol/L吗啡和100nmol/L DADLE阻断μ和δ受体)与阿片受体结合的抑制强度。结果表明:DHE对[~3H]纳洛酮与阿片受体结合的抑制强度远远大于对[~3H]DPDPE和[~3H]埃托啡(预先阻断μ和δ受体后)。DHE对μ,δ和κ受体的相对亲和力之比为1951:2:1,提示DHE为μ受体相对选择性配体。     

从远志中分离鉴定出一种多巴胺受体活性化合物

从中药远志中提出一种多巴胺受体的配基,四氢非州防己胺。此化合物在体外可抑制[³H]SCH23390和[³H]螺哌隆与大鼠纹状体膜的结合,IC₅₀值分别为0.75±0.08μmol·L^-1和0.92±0.10μmol·L^-1。它在体外还能抑制[³H]哌唑嗪和大鼠脑皮质细胞膜结合(IC₅₀值为46μmol·L^-1),但不能改变[³H]QNB及[³H]muscimol对膜的结合。Scatchandplot分析显示此化合物对[³H]SCH23390和[³H]螺哌隆与膜结合的抑制作用是通过竞争性与非竞争性混合机制而实现的。     

新抗胆碱药[~3H]三环哌酯对人脑M受体的作用

用放射配体受体结合试验法，研究了新化合物三环哌酯与人大脑皮质Ｍ受体的结合特性，并与ＱＮＢ作了比较。饱和实验结果显示，［３Ｈ］三环哌酯的结合参数与［３Ｈ］ＱＮＢ相近，两种配体的作用均符合单位点模型。竞争性抑制实验结果表明二者作用强度相当。［３Ｈ］三环哌酯的结合和解离速率常数均较［３Ｈ］ＱＮＢ大，且其与皮质Ｍ受体的解离受季铵酚的变构调节，结果提示，两种配体与Ｍ受体有一些不同的结合特性，在Ｍ受体研究中，［３Ｈ］三环哌酯可以作为［３Ｈ］ＱＮＢ的补充工具     

铅对发育脑纹状体毒蕈碱和多巴胺受体的影响

母鼠从受孕d0至分娩后d21连续饮用含300和1000ppm的铅水。新生大鼠出生后d21处死。结果表明,血和纹状体铅含量明显增加;在1000ppm组,DNA,RNA降低和蛋白质/DNA比值升高;纹状体DA含量亦减少。铅不影响[~3H]spiperone与纹状体DA受体的特异结合。但影响[~3H]QNB与MACh受体的特异结合,受体数目增加,亲和力未变,提示脑纹状体MACh受体功能状态与铅含量有关。铅影响发育脑纹状体的这两种受体的相互平衡,可能是铅对仔代神经毒性的原因之一。     

Interaction of antihistaminics with muscarinic receptor (III)

The muscarinic antagonist 1-[benzilic 4,4′-³H]quinuclidinyl benzilate ([³H] QNB) bound to a single class of muscarinic receptors with high affinity in rabbit ileal membranes. The K _D and B _max values for [³H]QNB calculated from analysis of saturation isotherms were 52.5 pM and 154 fmol/mg, respectively. Chlorpheniramine (CHP), histamine H₁ blocker, increased K _D value for [³H]QNB without affecting the binding site concentrations and Hill coefficient. The K _i value of CHP for inhibition of [³H]QNB binding in ileal membranes was 1.44μM and the pseudo-Hill coefficient for CHP was close to unit. In the functional assay carbachol, muscarinic agonist, increased the contractile force of ileum with ED₅₀ value of 0.11μM. CHP caused the rightward shift of the dose-response curve to carbachol. The pA₂ value of CHP determined from Schild analysis of carbachol-induced contraction was 5.77 and the slope was unity indicating competitive antagonism with carbachol. The dissociation constant (K _i ) of CHP obtained in competitive experiments with [³H]QNB was similar to the K _A value (1.69μM) of CHP as inhibitor of carbachol-induced contraction in rabbit ileum. This result suggests that the binding of H₁ blocker, CHP, vs [³H]QNB to muscarinic receptors in ileal membranes represents an interaction with a receptor of physiological relevance.     

Characteristics of 5-HT3 binding sites in NG108-15, NCB-20 neuroblastoma cells and rat cerebral cortex using [3H]-quipazine and [3H]-GR65630 binding.

1. The biochemical and pharmacological properties of 5-HT3 receptors in homogenates of NG108-15 and NCB-20 neuroblastoma cells and rat cerebral cortex have been ascertained by the use of [3H]-quipazine and [3H]-GR65630 binding. 2. In NG108-15 and NCB-20 cell homogenates, [3H]-quipazine bound to a single class of high affinity (NG108-15: Kd = 6.2 +/- 1.1 nM, n = 4; NCB-20: Kd = 3.0 +/- 0.9 nM, n = 4; means +/- s.e.means) saturable (NG108-15: Bmax = 1340 +/- 220 fmol mg-1 protein; NCB-20: Bmax = 2300 +/- 200 fmol mg-1 protein) binding sites. In rat cortical homogenates, [3H]-quipazine bound to two populations of binding sites in the absence of the 5-hydroxytryptamine (5-HT) uptake inhibitor, paroxetine (Kd1 = 1.6 +/- 0.5 nM, Bmax1 = 75 +/- 14 fmol mg-1 protein; Kd2 = 500 +/- 300 nM, Bmax2 = 1840 +/- 1040 fmol mg-1 protein, n = 3), and to a single class of high affinity binding sites (Kd = 2.0 +/- 0.5 nM, n = 3; Bmax = 73 +/- 6 fmol mg-1 protein) in the presence of paroxetine. The high affinity (nanomolar) component probably represented 5-HT3 binding sites and the low affinity component represented 5-HT uptake sites. 3. [3H]-paroxetine bound with high affinity (Kd = 0.02 +/- 0.003 nM, n = 3) to a site in rat cortical homogenates in a saturable (Bmax = 323 +/- 45 fmol mg-1 protein, n = 3) and reversible manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Developmental changes in beta-adrenoceptors, muscarinic cholinoceptors and Ca2+ channels in rat ventricular muscles.

1. In an attempt to explain the previous electrophysiological data on the ontogeny of beta-adrenergic and muscarinic cholinergic interactions on cardiac Ca2+ current, biochemical studies were performed on the ontogeny of beta-adrenoceptors, muscarinic cholinoceptors and Ca2+ channels in cardiac muscle of developing rats: 16-20 days old foetuses, 0-20 days old neonates, and 2-3 months old adults. 2. Developmental changes in cardiac beta-adrenoceptors, muscarinic cholinoceptors, and Ca2+ channels were determined with the use of specific radioligands, [3H]-dihydroalprenolol (DNA), [3H]-quinuclidinyl benzilate (QNB), and [3H]-nitrendipine (NTD), respectively. 3. The Bmax value (fmol mg-1 tissue) for [3H]-DNA binding started to increase on post-gestation day 20, reached almost its maximum level on neonatal day 6, kept almost the same level until neonatal day 20, and then decreased slightly to its adult level. 4. The Bmax value (fmol mg-1 tissue) for [3H]-QNB binding started to increase on post-gestation day 16, reached almost its maximum level on neonatal day 0, remained almost constant until neonatal day 15, and then decreased to its adult level. 5. The Bmax value (fmol mg-1 tissue) for [3H]-NTD binding increased with age between post-gestation day 18 and neonatal day 15, stayed almost constant until neonatal day 20, and then decreased to its adult level. 6. The Kd values for [3H]-DHA, [3H]-QNB, and [3H]-NTD bindings remained almost constant during the developmental period examined.(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscarinic receptors of the vascular bed: radioligand binding studies on bovine splenic veins

Despite an obvious lack of parasympathetic innervation to the spleen, pharmacological evidence suggests the presence of cholinergic receptors in isolated bovine splenic veins. We therefore studied muscarinic cholinergic binding sites in a bovine splenic vein preparation by direct radioligand binding techniques using [3H]quinuclidinyl benzilate ([3H]QNB) as radioactive probe. Saturation experiments indicated one homogeneous class of high-affinity binding sites, with a KD of 0.11 nM and a binding site density Bmax of 55 fmol/mg protein. The rate constants at 37 degrees C for formation and dissociation of the [3H]QNB receptor complex were 2.7 X 10(9) M-1 h-1 and 0.38 h-1, respectively, yielding a KD of 0.14 nM. The binding sites showed a high stereospecificity, which was evident from competition experiments with dexetimide (KI = 1.3 nM) and levetimide (KI = 4.6 microM). In competition experiments with muscarinic and nicotinic antagonists and some antidepressants, only one binding site was found, whereas with muscarinic agonists, two binding sites were detected. In the presence of 0.1 mM guanyl-imido-diphosphate, only one binding site could be identified with the muscarinic agonist carbamylcholine. The affinity of [3H]QNB, on the other hand, was slightly decreased, and Bmax values were unchanged. It is concluded that specific, saturable, high-affinity muscarinic binding sites in the bovine splenic vein have been identified and characterized that exhibit properties similar to cholinergic receptors of brain and peripheral tissues and probably mediate acetylcholine-induced relaxation of splenic veins.     

Characterization of cholinergic muscarinic receptors in cow tracheal muscle membranes. Effect of maturation

The parasympathetic nervous system is important in the control of basal airway muscle tone and caliber. We characterized muscarinic cholinergic receptors in isolated tracheal membranes from cows of three age groups (immature, less than 2 weeks; transition, 3-5 months; and mature, greater than 5 years) using l-[3H]quinuclidinyl benzilate (l-[3H]QNB) as the radioligand. There were significant decreases in the densities of l-[3H]QNB binding sites with maturation (Bmax: 2344 +/- 169 vs 1381 +/- 85 vs 1116 +/- 80 fmol/mg protein for tissues from immature, transition and mature cows respectively). No change in the dissociation constant was observed with maturation (Kd: 0.38 +/- 0.09 vs 0.55 +/- 0.06 vs 0.50 +/- 0.07 nM for tissues from immature, transition and mature animals respectively). The association and dissociation rate constants did not vary between tissues from immature and mature animals. The specific activity of the enzyme, acetylcholinesterase, was correlated with the density of l-[3H]QNB binding sites present in the tracheal homogenates; that is, with maturation, there were significant decreases in acetylcholinesterase activity [0.28 +/- 0.01 vs 0.16 +/- 0.02 vs 0.08 +/- 0.01 mol X l-1 X min-1 X (mg protein)-1 for tissues from immature, transition and mature animals respectively]. All competition binding studies using muscarinic antagonists exhibited single site binding and did not show any differences in drug affinities between the age groups. In contrast, multiple binding sites were observed with carbachol, methacholine and muscarine, and there were significant decreases in receptor affinities for the muscarinic agonists. No changes in the proportion of high and low affinity sites were found. These results indicate that with maturation there are alterations in the properties of muscarinic receptors in tracheal smooth muscle.     

Identification of drug receptors in porcine dental pulp by the radioligand binding assay

1. The acetylcholine (ACh), histamine and serotonin (5-HT) receptors in porcine dental pulp were characterized by the radioligand binding assay. 2. For [3H]nicotine binding site, Kd was 8.06 +/- 1.65 nM and Bmax was 270.83 +/- 32.68 fmol/mg protein. 3. For [3H]QNB binding site, Kd was 1.04 +/- 0.14 nM and Bmax was 24.83 +/- 3.09 fmol/mg protein. 4. For [3H]histamine binding site, Kd was 1.22 +/- 0.1 nM and Bmax was 283.15 +/- 33.1 fmol/mg protein. 5. For [3H]5-HT binding site, Kd was 1.41 +/- 0.1 nM and Bmax was 53.1 +/- 3.4 fmol/mg protein. 6. These findings indicate that the specific receptors for ACh, histamine and 5-HT are present in the porcine dental pulp, and that the ACh receptor is predominantly nicotinic.     

Alpha 2-adrenoceptor subtypes and imidazoline-like binding sites in the rat brain.

1. The binding of [3H]-yohimbine and [3H]-idazoxan to rat cortex and hippocampus is rapid, reversible and of high affinity. Saturation data indicate that a single population of binding sites exist for [3H]-yohimbine in the cortex (Bmax 121 +/- 10 fmol mg-1, protein; Kd 5.2 +/- 0.9 nM) and hippocampus (Bmax 72 +/- 6 fmol mg-1 protein; Kd 5.8 +/- 0.7 nM). [3H]-idazoxan labels one site in the cortex (Bmax 87 +/- 8 fmol mg-1 protein; Kd 4.1 +/- 0.9 nM) and hippocampus (Bmax 30 +/- 6 fmol mg-1 protein; Kd 3.5 +/- 0.5 nM), when 3 microM phentolamine is used to define non-specific binding. A second distinct [3H]-idazoxan binding site (Bmax 110 +/- 21 fmol mg-1 protein; Kd 3.6 +/- 0.07 nM) is identified in rat cortex if 0.3 microM cirazoline is used to define non-specific binding and 3 microM yohimbine is included to prevent binding to alpha 2-adrenoceptors. 2. Displacement studies indicate that the alpha 1-adrenoceptor antagonist prazosin and the 5-HT1 ligands 8-OH-DPAT, RU 24969 and methysergide differentiate [3H]-yohimbine binding into two components; a high and low affinity site. In contrast the displacement of [3H]-idazoxan by each ligand was monophasic. 3. The affinities of 8-OH-DPAT, RU 24969 and methysergide determined against [3H]-idazoxan binding to the cortex and hippocampus correlate significantly with the binding site displaying low affinity for prazosin and previously designated alpha 2A. In contrast, a poor correlation exists for the high affinity site for prazosin designated alpha 2B.(ABSTRACT TRUNCATED AT 250 WORDS)     

High- and low-affinity binding sites for [3H]-alpha, beta-methylene ATP in rat urinary bladder membranes.

1. The characteristics of [3H]-alpha, beta-methylene adenosine 5'triphosphate ([3H]-alpha, beta-MeATP) binding to membrane preparations of rat urinary bladder detrusor were studied. 2. The rat bladder membrane preparation was obtained by multiple centrifugation. [3H]-quinuclidinyl benzilate [( 3H]-QNB) binding to this preparation demonstrated that the muscarinic receptor density was 4.32 times higher than that in the homogenate. [3H]-alpha, beta-MeATP binding was increased 3.88 times. 3. Saturation analysis revealed that the rat bladder membrane contained a high density of [3H]-alpha, beta-MeATP binding sites, which could be divided into a high-affinity component (Kd = 8.1-8.9 nM) and a low-affinity component (Kd = 67.0-119.8 nM). 4. Magnesium ions inhibited the maximum binding in a concentration-dependent manner. The maximum high-affinity binding was reduced from 10.32 pmol mg-1 protein in magnesium-free buffer to 4.62 pmol mg-1 protein with 25 mM MgCl2, while the maximum low-affinity binding was reduced from 58.84 pmol mg-1 protein to 14.24 pmol mg-1 protein. Kd values were not greatly affected. 5. The binding was a rapid reversible process. The association rate constants were 7.64 x 10(7) M-1 min-1 for high-affinity binding, and 7.31 x 10(6) M-1 min-1 for low-affinity binding. The dissociation rate constants were 0.2896 min-1 for high-affinity binding, and 0.6348 min-1 for the low-affinity binding. 6. Displacement experiments with unlabelled purinoceptor ligands confirmed that [3H]-alpha, beta-MeATP mainly binds to P2X-purinoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Binding studies with [3H]cis-methyldioxolane in different tissues

Summary Special conditions - tricine buffer containing Ca²⁺ and Mg²⁺, 22°C (TCM) — allow to label a much higher proportion of muscarinic receptors by [³H]cis-methyldioxolane (CD) than hitherto described (Vickroy et al. 1984 a). Taking the maximum number of binding sites, B _max, of [³H]QNB as 100%, B _max of [³H]CD amounts to 83% in the rat heart instead of the reported 17%, 33% in the cerebral cortex instead of 6%, 20% in hippocampus and 55% in pons/medulla. In the salivary glands specific binding was negligible. The affinities of a number of muscarinic agonists and antagonists to [³H]CD and [³H]QNB binding sites in different tissues of the rat are compared. Apparent affinities of agonists are much higher in the [³H]CD system, affinities of antagonists are slightly higher in the [³H]QNB system. In both assay systems receptors of heart and pons/ medulla membranes seem to have similar drug specificity. They differ somewhat from those in the cortex. Receptors in the salivary glands, however, seem to be completely different from those in the other three tissues. In the heart [³H]CD binding can be abolished almost completely by GppNHp. In the cortex about half of the [³H]CD binding is susceptible to GppNHp. The reduction of binding in the cortex is due to a change in B _max and not in the dissociation constant K _D. Competition of unlabelled pirenzepine with [³H]CD: In heart and pons/medulla only low affinity sites for pirenzepine (M₂-receptors) are labelled by [³H]CD. In regions rich in M₁ receptors like hippocampus (80% M₁ receptors) or cortex (65–70% M₁ receptors) the proportion of M₁ receptors labelled by [³H]CD is smaller than expected considering the concentration of M₁ receptors present in these tissues. Thus [³H]CD, under the conditions described in this paper, seems to label preferentially but not exclusively M₂ receptors in their agonist high affinity form. Send offprint requests to A. Closse at the above address     

Muscarinic receptor binding characteristics in rat tissues after oral administration of oxybutynin and propiverine

Ex vivo muscarinic receptor binding of oxybutynin and propiverine, the most commonly used anticholinergic agents for the treatment in patients with urinary incontinence, was investigated in rat tissues. The oral administration of oxybutynin (50.8 and 127 micromol/kg) caused a significant increase in the apparent dissociation constant (Kd) for specific (-)-[3H]QNB binding in the rat bladder, prostate, submaxillary gland, heart and cerebral cortex, compared with each of the control values. Also, in the submaxillary gland of these rats, there was a reduction in the maximal number of binding sites (Bmax) for (-)-[3H]QNB binding. Similarly, oral administration of propiverine at doses of 74.3-297 micromol/kg brought about a significant increase in the Kd values for (-)-[3H]QNB binding in rat tissues including the bladder, and greater increase in Kd values was seen in the rat prostate, heart and submaxillary gland. On the other hand, oral administration of propiverine, unlike oxybutynin, resulted in very little reduction in the Bmax valules for (-)-[3H]QNB binding in the submaxillary gland. In conclusion, the present study has shown that oxybutynin and propiverine, after oral administration, bind significantly to muscarinic receptors in tissues such as the bladder, which is the target organ for the treatment of urinary incontinence, and that oxybutynin appears to exhibit long-term binding to muscarinic receptors in the salivary gland.