Katsube Y, Yokoshiki H, Sunagawa M, Seki T, Yamamoto M, Sperelakis N
Department of Pediatrics, Nippon Medical School Hospital, Tokyo, Japan.
Eur J Pharmacol. 1998 Oct 9;358(3):269-75. doi: 10.1016/s0014-2999(98)00605-0.
We investigated the postnatal developmental changes produced by the muscarinic receptor agonist, carbachol, on the L-type Ca2+ current (ICa(L)) in neonatal (aged 5 to 7 days) and adult (aged 2 to 5 months) rat ventricular cells by using the whole-cell voltage clamp technique. Carbachol inhibited the isoproterenol-stimulated ICa(L). The maximal inhibition was 89.3 +/- 4.8% (n = 5) in neonatal cells and 17.7 +/- 7.7% (n = 9) in adult cells. Carbachol inhibited the forskolin-stimulated ICa(L) to almost same extent as the isoproterenol-stimulated ICa(L). In the cells pretreated with pertussis toxin, carbachol failed to inhibit the isoproterenol-stimulated ICa(L), indicating that carbachol produced its effect via a pertussis toxin-sensitive G-protein pathway. The effects of carbachol in adult cells became more pronounced, increasing from 17.7% to 54.8% (n = 11), with the addition of the synthetic inhibitory G-protein alpha subunit (Gi alpha) (1 microM) to the reaction. Conversely, the alpha subunit of another pertussis toxin-sensitive synthetic G-protein (G(o) alpha, 1 microM) failed to mimic the effect of Gi alpha. These results suggest that, in rat ventricular cells, (1) the action of carbachol on ICa(L) showed a marked decrease during development; (2) the decrease in the effect of carbachol in adult cells is in part due to a decrease in the activity of pertussis toxin-sensitive G protein, especially Gi alpha.
我们采用全细胞电压钳技术，研究了毒蕈碱受体激动剂卡巴胆碱对新生（5至7日龄）和成年（2至5月龄）大鼠心室细胞L型钙电流（ICa(L)）的产后发育变化。卡巴胆碱抑制异丙肾上腺素刺激的ICa(L)。新生细胞中的最大抑制率为89.3±4.8%（n = 5），成年细胞中的最大抑制率为17.7±7.7%（n = 9）。卡巴胆碱对福斯可林刺激的ICa(L)的抑制程度与对异丙肾上腺素刺激的ICa(L)的抑制程度几乎相同。在用百日咳毒素预处理的细胞中，卡巴胆碱未能抑制异丙肾上腺素刺激的ICa(L)，这表明卡巴胆碱是通过百日咳毒素敏感的G蛋白途径发挥作用的。在反应中加入合成抑制性G蛋白α亚基（Giα，1μM）后，卡巴胆碱对成年细胞的作用变得更加明显，从17.7%增加到54.8%（n = 11）。相反，另一种百日咳毒素敏感的合成G蛋白的α亚基（G(o)α，1μM）未能模拟Giα的作用。这些结果表明，在大鼠心室细胞中，（1）卡巴胆碱对ICa(L)的作用在发育过程中显著降低；（2）成年细胞中卡巴胆碱作用的降低部分归因于百日咳毒素敏感G蛋白，尤其是Giα活性的降低。
