Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, USA.
Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA.
Physiol Rep. 2021 Feb;9(4):e14754. doi: 10.14814/phy2.14754.
During development, maturation, or aging, the expression and function of urinary bladder smooth muscle (UBSM) ion channels can change, thus affecting micturition. Increasing evidence supports a novel role of transient receptor potential melastatin-4 (TRPM4) channels in UBSM physiology. However, it remains unknown whether the functional expression of these key regulatory channels fluctuates in UBSM over different life stages. Here, we examined TRPM4 channel protein expression (Western blot) and the effects of TRPM4 channel inhibitors, 9-phenanthrol and glibenclamide, on phasic contractions of UBSM isolated strips obtained from juvenile (UBSM-J, 5-9 weeks old) and adult (UBSM-A, 6-18 months old) male guinea pigs. Compared to UBSM-J, UBSM-A displayed a 50-70% reduction in total TRPM4 protein expression, while the surface-to-intracellular expression ratio (channel trafficking) remained the same in both age groups. Consistent with the reduced total TRPM4 protein expression in UBSM-A, 9-phenanthrol showed lower potencies and/or maximum efficacies in UBSM-A than UBSM-J for inhibiting amplitude and muscle force of spontaneous and 20 mM KCl-induced phasic contractions. Compared to 9-phenanthrol, glibenclamide also attenuated both spontaneous and KCl-induced contractions, but with less pronounced differential effects in UBSM-A and UBSM-J. In both age groups, regardless of the overall reduced total TRPM4 protein expression in UBSM-A, cell surface TRPM4 protein expression (80%) predominated over its intracellular fraction (20%), revealing preserved channel trafficking mechanisms toward the cell membrane. Collectively, this study reports novel findings illuminating a fundamental physiological role for TRPM4 channels in UBSM function that fluctuates with age.
在发育、成熟或衰老过程中，尿膀胱平滑肌（UBSM）离子通道的表达和功能可能会发生变化，从而影响排尿。越来越多的证据支持瞬时受体电位 melastatin-4（TRPM4）通道在 UBSM 生理学中的新作用。然而，这些关键调节通道在 UBSM 中不同生命阶段的功能表达是否波动仍不清楚。在这里，我们检查了 TRPM4 通道蛋白表达（Western blot）以及 TRPM4 通道抑制剂 9- 菲咯啉和格列本脲对从小鼠（UBSM-J，5-9 周龄）和成年（UBSM-A，6-18 月龄）雄性豚鼠分离的 UBSM 条带的相位收缩的影响。与 UBSM-J 相比，UBSM-A 的总 TRPM4 蛋白表达减少了 50-70%，而两组的表面到细胞内表达比（通道转运）保持不变。与 UBSM-A 中总 TRPM4 蛋白表达减少一致，9-菲咯啉对自发和 20 mM KCl 诱导的相位收缩的幅度和肌肉力的抑制作用在 UBSM-A 中的效力和/或最大效力均低于 UBSM-J。与 9-菲咯啉相比，格列本脲也减弱了自发性和 KCl 诱导的收缩，但在 UBSM-A 和 UBSM-J 中差异作用不明显。在两个年龄组中，无论 UBSM-A 中的总 TRPM4 蛋白表达总体减少，细胞表面 TRPM4 蛋白表达（80%）均超过其细胞内部分（20%），表明向细胞膜的通道转运机制得以保留。总的来说，这项研究报告了新的发现，阐明了 TRPM4 通道在 UBSM 功能中的基本生理作用随年龄而波动。
