Dept. of Pharmaceutical & Biomedical Sciences, South Carolina College of Pharmacy, Univ. of South Carolina, Columbia, SC 29208, USA.
Am J Physiol Renal Physiol. 2012 Nov 1;303(9):F1300-6. doi: 10.1152/ajprenal.00351.2012. Epub 2012 Aug 15.
Pharmacological blockade of cyclic nucleotide phosphodiesterase (PDE) can relax human urinary bladder smooth muscle (UBSM); however, the underlying cellular mechanism is unknown. In this study, we investigated the effects of PDE pharmacological blockade on human UBSM excitability, spontaneous and nerve-evoked contractility, and determined the underlying cellular mechanism mediating these effects. Patch-clamp electrophysiological experiments showed that 3-isobutyl-1-methylxanthine (10 μM), a nonselective PDE inhibitor, caused ∼3.6-fold increase in the transient K(Ca)1.1 channel current frequency and ∼2.5-fold increase in the spontaneous transient hyperpolarization frequency in UBSM-isolated cells. PDE blockade also caused ∼5.6-mV hyperpolarization of the UBSM cell membrane potential. Blocking the K(Ca)1.1 channels with paxilline abolished the spontaneous transient hyperpolarization and the hyperpolarization effect of PDE blockade on the UBSM cell membrane potential. Live cell Ca(2+)-imaging experiments showed that PDE blockade significantly decreased the global intracellular Ca(2+) levels. Attenuation of PDE activity significantly reduced spontaneous phasic contraction amplitude, muscle force integral, duration, frequency, and muscle tone of human UBSM isolated strips. Blockade of PDE also significantly reduced the contraction amplitude, muscle force integral, and duration of the nerve-evoked contractions induced by 20-Hz electrical field stimulation. Pharmacological inhibition of K(Ca)1.1 channels abolished the relaxation effects of PDE blockade on both spontaneous and nerve-evoked contractions in human UBSM-isolated strips. Our data provide strong evidence that in human UBSM PDE is constitutively active, thus maintaining spontaneous UBSM contractility. PDE blockade causes relaxation of human UBSM by increasing transient K(Ca)1.1 channel current activity, hyperpolarizing cell membrane potential, and decreasing the global intracellular Ca(2+).
磷酸二酯酶（PDE）的药理学阻断可以使人类膀胱平滑肌（UBSM）松弛；然而，其潜在的细胞机制尚不清楚。在这项研究中，我们研究了 PDE 药理学阻断对人 UBSM 兴奋性、自发性和神经诱发收缩性的影响，并确定了介导这些影响的潜在细胞机制。膜片钳电生理实验表明，非选择性 PDE 抑制剂 3-异丁基-1-甲基黄嘌呤（10 μM）可使 UBSM 分离细胞中的瞬时 K(Ca)1.1 通道电流频率增加约 3.6 倍，自发性瞬时超极化频率增加约 2.5 倍。PDE 阻断还可使 UBSM 细胞膜电位发生约 5.6 mV 的超极化。用 paxilline 阻断 K(Ca)1.1 通道可消除自发性瞬时超极化和 PDE 阻断对 UBSM 细胞膜电位的超极化作用。活细胞 Ca(2+)成像实验表明，PDE 阻断显著降低了细胞内整体 Ca(2+)水平。抑制 PDE 活性显著降低了人 UBSM 分离条带的自发性相位收缩幅度、肌肉力积分、持续时间、频率和肌肉紧张度。PDE 阻断也显著降低了 20-Hz 电场刺激诱导的神经诱发收缩的收缩幅度、肌肉力积分和持续时间。K(Ca)1.1 通道的药理学抑制消除了 PDE 阻断对人 UBSM 分离条带的自发性和神经诱发收缩的松弛作用。我们的数据提供了强有力的证据表明，在人类 UBSM 中，PDE 是组成性激活的，从而维持自发性 UBSM 收缩性。PDE 阻断通过增加瞬时 K(Ca)1.1 通道电流活性、超极化细胞膜电位和降低细胞内整体 Ca(2+)来松弛人 UBSM。
