Kizawa Y, Shinkai M, Takayanagi I
Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
Can J Physiol Pharmacol. 1990 Jan;68(1):99-103. doi: 10.1139/y90-015.
Nicotine induced a phasic contraction in the rabbit urinary bladder. The response was abolished by hexamethonium and partially reduced by atropine and capsaicin. Simultaneous atropine and capsaicin treatment did not abolish the contraction. These findings suggest that the response to nicotine is due to acetylcholine, tachykinins, and unknown mediator release. In contrast, nicotine-induced contraction diminished following the chronic nicotine treatment without a change of its pharmacological properties. These results suggest the possibility that chronic nicotine treatment causes a decrease in nicotinic receptor numbers. Therefore, the binding properties of (-)-[3H]nicotine on rabbit urinary detrusor muscle membrane fractions were studied to evaluate the effects of chronic nicotine treatment on nicotinic receptors. Specific (-)-[3H]nicotine binding reached saturation and Scatchard plots were curvilinear, suggesting the existence of two different affinity sites for (-)-[3H]nicotine. Dissociation constants (KD) and maximum binding sites (Bmax) were KD1 = 4.91 +/- 1.88 nM, Bmax1 = 2.42 +/- 0.22 fmol/mg protein and KD2 = 263 +/- 56 nM, Bmax2 = 25.0 +/- 4.3 fmol/mg protein. In urinary bladder membrane fractions from chronic nicotine-treated rabbits, KD and Bmax values were KD1 = 3.96 +/- 0.38 nM, Bmax1 = 1.07 +/- 0.25 fmol/mg protein and KD2 = 249 +/- 12 nM, Bmax2 = 10.8 +/- 1.5 fmol/mg protein. Dissociation constants for both sites following chronic nicotine treatment did not change but maximum binding site numbers for both sites significantly decreased (p less than 0.05). These results suggest that the decrease in contractile response evoked by nicotine after chronic nicotine treatment in rabbit urinary bladder is due to a decrease in numbers of nicotinic receptors.
尼古丁可引起兔膀胱的阶段性收缩。六甲铵可消除该反应，阿托品和辣椒素可使其部分减弱。同时给予阿托品和辣椒素治疗并不能消除收缩反应。这些发现表明，对尼古丁的反应是由于乙酰胆碱、速激肽和未知介质的释放所致。相比之下，慢性尼古丁治疗后，尼古丁诱导的收缩减弱，但其药理特性未发生改变。这些结果提示，慢性尼古丁治疗可能导致烟碱受体数量减少。因此，研究了（-）-[³H]尼古丁在兔膀胱逼尿肌膜组分上的结合特性，以评估慢性尼古丁治疗对烟碱受体的影响。特异性（-）-[³H]尼古丁结合达到饱和，Scatchard图呈曲线状，表明存在两个不同的（-）-[³H]尼古丁亲和位点。解离常数（KD）和最大结合位点（Bmax）分别为KD1 = 4.91±1.88 nM，Bmax1 = 2.42±0.22 fmol/mg蛋白，KD2 = 263±56 nM，Bmax2 = 25.0±4.3 fmol/mg蛋白。在慢性尼古丁处理兔的膀胱膜组分中，KD和Bmax值分别为KD1 = 3.96±0.38 nM，Bmax1 = 1.07±0.25 fmol/mg蛋白，KD2 = 249±12 nM，Bmax2 = 10.8±1.5 fmol/mg蛋白。慢性尼古丁处理后两个位点的解离常数未发生变化，但两个位点的最大结合位点数均显著减少（p < 0.05）。这些结果表明，兔膀胱经慢性尼古丁处理后，尼古丁引起的收缩反应减弱是由于烟碱受体数量减少所致。
