Lam P M W, McDonald J, Lambert D G
Department of Cardiovascular Sciences, Pharmacology and Therapeutics Group, Division of Anaesthesia, Critical Care and Pain Management, University of Leicester, Leicester Royal Infirmary, LE1 5WW, UK.
Br J Anaesth. 2005 May;94(5):649-56. doi: 10.1093/bja/aei098. Epub 2005 Feb 18.
TRPV1 is a ligand-gated ion channel whose activation by capsaicin increases intracellular Ca(2+) (Ca(2+)). TRPV1 and cannabinoid CB(1) receptor activation are capable of eliciting analgesia. In this study, using recombinant human (h) and rat (r) TRPV1 receptors expressed in HEK293 cells, we have performed a comparison of both TRPV1 species at 22 and 37 degrees C and compared endo- and exocannabinoid activity at both receptors.
Ca(2+) was measured in Fura-2-loaded HEK293(hTRPV1) and HEK293(rTRPV1) cells. To assess native CB(1) receptor activity, [(35)S]GTPgammaS binding to membranes prepared from rat cerebellum was measured.
Both capsaicin (pEC(50) rat approximately 6.9 and pEC(50) human approximately 6.8 at 37 degrees C) and anandamide (pEC(50) rat approximately 5.3 and pEC(50) human approximately 5.8 at 37 degrees C) produced a concentration-dependent increase in Ca(2+) in rat and human systems and at 22 and 37 degrees C. In HEK293(rTRPV1) cells, anandamide appeared to be a partial agonist. Capsazepine demonstrated competitive antagonism at both human and rat TRPV1 receptors and at both temperatures studied. Capsazepine effects were not temperature dependent: pK(B) at rTRPV1 was 5.98 at 22 degrees C and 6.02 at 37 degrees C, and pK(B) at hTRPV1 was 6.76 at 22 degrees C and 6.75 at 37 degrees C. However, there was a consistent 6-fold increase in capsazepine potency for hTRPV1 relative to rTRPV1. The exocannabinoid Delta(9)-tetrahydrocannabinol failed to increase Ca(2+), although its solvent ethanol was an effective TRPV1 activator. In the [(35)S]GTPgammaS binding assay using rat cerebellar membranes, anandamide (pEC(50) approximately 5.8) and Delta(9)-tetrahydrocannabinol (pEC(50) approximately 7.1), but not capsaicin, stimulated binding. Delta(9)-tetrahydrocannabinol was a partial agonist. pEC(50) values for anandamide at rTRPV1 and rCB(1) were similar.
There were small differences in the pharmacology of rat and human TRPV1 receptors. Whilst capsaicin activated TRPV1 and Delta(9)-tetrahydrocannabinol activated CB(1), anandamide is an endogenous agonist for both receptor systems.
TRPV1是一种配体门控离子通道，辣椒素对其激活可增加细胞内钙离子浓度（[Ca(2+)]i）。TRPV1和大麻素CB(1)受体的激活均能够产生镇痛作用。在本研究中，我们利用在HEK293细胞中表达的重组人（h）和大鼠（r）TRPV1受体，在22℃和37℃下对这两种TRPV1进行了比较，并比较了两种受体上内源性和外源性大麻素的活性。
在负载Fura-2的HEK293（hTRPV1）和HEK293（rTRPV1）细胞中测量[Ca(2+)]i。为评估天然CB(1)受体活性，测量了[35S]GTPγS与从大鼠小脑制备的膜的结合情况。
辣椒素（37℃时大鼠的pEC(50)约为6.9，人约为6.8）和花生四烯乙醇胺（37℃时大鼠的pEC(50)约为5.3，人约为5.8）在大鼠和人类系统中以及22℃和37℃时均使[Ca(2+)]i呈浓度依赖性增加。在HEK293（rTRPV1）细胞中，花生四烯乙醇胺似乎是部分激动剂。辣椒平在研究的两个温度下对人和大鼠TRPV1受体均表现出竞争性拮抗作用。辣椒平的作用不依赖温度：rTRPV1在22℃时的pK(B)为5.98，37℃时为6.02；hTRPV1在22℃时的pK(B)为6.76，37℃时为6.75。然而，相对于rTRPV1，辣椒平对hTRPV1的效力持续增加6倍。外源性大麻素Δ9-四氢大麻酚未能增加[Ca(2+)]i，尽管其溶剂乙醇是有效的TRPV1激活剂。在使用大鼠小脑膜的[35S]GTPγS结合试验中，花生四烯乙醇胺（pEC(50)约为5.8）和Δ9-四氢大麻酚（pEC(50)约为7.1）刺激了结合，但辣椒素未刺激。Δ9-四氢大麻酚是部分激动剂。花生四烯乙醇胺在rTRPV1和rCB(1)上的值相似。
大鼠和人类TRPV1受体的药理学存在微小差异。虽然辣椒素激活TRPV1，Δ9-四氢大麻酚激活CB(1)，但花生四烯乙醇胺是两种受体系统的内源性激动剂。
