Sugita M, Tokutomi N, Tokutomi Y, Terasaki H, Nishi K
Department of Anesthesiology, Kumamoto University School of Medicine, Honjo, Japan.
Eur J Pharmacol. 1998 May 1;348(1):61-70. doi: 10.1016/s0014-2999(98)00129-0.
Freshly dissociated bladder smooth muscle cells of mice developed spontaneous, caffeine- (ICAF) and carbachol-induced (ICCh) currents under voltage-clamped conditions. Spontaneous currents, ICAF and ICCh were blocked with tetraethylammonium at 3 x 10(-4)-10(-2) M but were resistant to both charybdotoxin (10(-7)-10(-6) M) and iberiotoxin (10(-7)-10(-6) M). The reversal potential for each current indicated that K+ channels play a major role in the generation of each current. Both spontaneous currents and ICAF but not ICCh were abolished in nominally Ca2+-free and nicardipine (10(-6) M)-containing media. These results suggest that the activity of L-type voltage-sensitive Ca2+ channels is important in the generation and maintenance of spontaneous currents and ICAF but not ICCh. Ryanodine (10(-6) M) prevented spontaneous currents, ICAF and caffeine-induced [Ca2+]i elevation but not ICCh and carbachol-induced [Ca2+]i elevation, suggesting that the response of bladder smooth muscle cells to carbachol may involve a Ca2+ store distinct from that for caffeine. Pretreatment with carbachol suppressed ICAF to 22 +/- 7% (n = 7) and the caffeine-induced [Ca2+]i elevation to 25 + 3% (n = 6). Similarly, caffeine suppressed ICCh to 23 +/- 4% (n = 9) and the carbachol-induced [Ca2+]i elevation to 24 +/- 6% (n = 6).
在电压钳制条件下，新鲜分离的小鼠膀胱平滑肌细胞会产生自发电流、咖啡因诱导电流（ICAF）和卡巴胆碱诱导电流（ICCh）。自发电流、ICAF和ICCh在3×10⁻⁴ - 10⁻² M的四乙铵作用下被阻断，但对10⁻⁷ - 10⁻⁶ M的蝎毒素和10⁻⁷ - 10⁻⁶ M的埃博毒素均有抗性。每种电流的反转电位表明钾通道在每种电流的产生中起主要作用。在名义上无钙且含有尼卡地平（10⁻⁶ M）的培养基中，自发电流和ICAF均被消除，但ICCh不受影响。这些结果表明，L型电压敏感性钙通道的活性在自发电流和ICAF的产生和维持中很重要，但在ICCh中并非如此。ryanodine（10⁻⁶ M）可阻止自发电流、ICAF和咖啡因诱导的[Ca²⁺]i升高，但不能阻止ICCh和卡巴胆碱诱导的[Ca²⁺]i升高，这表明膀胱平滑肌细胞对卡巴胆碱的反应可能涉及与咖啡因不同的钙库。用卡巴胆碱预处理可将ICAF抑制至22±7%（n = 7），并将咖啡因诱导的[Ca²⁺]i升高抑制至25 + 3%（n = 6）。同样，咖啡因可将ICCh抑制至23±4%（n = 9），并将卡巴胆碱诱导的[Ca²⁺]i升高抑制至24±6%（n = 6）。
