Schnabel P, Gäs H, Nohr T, Camps M, Böhm M
Klinik III für Innere Medizin, Universität zu Köln, Germany.
J Mol Cell Cardiol. 1996 Dec;28(12):2419-27. doi: 10.1006/jmcc.1996.0235.
The generation of the second messengers inositol 1,4,5-trisphosphate (InsP3) and diacylglycerol (DAG) by phosphoinositide-specific phospholipases C (PLCs) is a key mechanism by which many cellular functions such as intracellular calcium handling or growth and differentiation are modulated. In the myocardium, PLC plays a role in the mediation of positive inotropic effects and is possibly involved in the pathogenesis of myocardial hypertrophy. Among the variety of PLC isozymes known, the PLC beta family is regulated by heterotrimeric G proteins. The aim of the present study was to identify and to characterize the PLC beta isoform present in human myocardium. PLC activity in human myocardial membranes was dependent on the presence of Ca2+. Interestingly, PLC was markedly stimulated by GTP gamma S, used as an activator of G proteins. This stimulation was completely abolished by GDP. However, purified alpha-subunits from retinal transducin (alpha 1), used as scavengers of free beta gamma-subunits, did not abolish this effect indicating GTP gamma S stimulation being mediated by G protein alpha-subunits. PLC activity was also stimulated by G protein beta gamma-subunits purified from bovine retina (beta gamma t). This stimulation was completely blocked by addition of purified alpha t. Reverse transcriptions and polymerase chain reactions (RT-PCR) provided evidence for PLC beta 1 mRNA being expressed in human myocardium, whereas PCR products corresponding to PLC beta 2 and PLC beta 3 mRNAs were not detected. It is concluded that PLC beta 1 mRNA is expressed in human myocardium. The functional properties of human myocardial PLC activity correspond well to the properties established for PLC beta 1, i.e. sensitivity to G protein alpha-as well as beta gamma-subunits. The presence of other as yet unidentified PLC isozymes is nevertheless possible. The identification of the PLC beta isozyme present in human myocardium and the understanding of its regulation by G protein subunits sets the stage for the investigation of possible involvement of this system in the pathophysiology of myocardial hypertrophy.
磷酸肌醇特异性磷脂酶C（PLCs）生成第二信使肌醇1,4,5-三磷酸（InsP3）和二酰基甘油（DAG）是一种关键机制，通过该机制可调节许多细胞功能，如细胞内钙处理或生长与分化。在心肌中，PLC在介导正性肌力作用中发挥作用，并且可能参与心肌肥大的发病机制。在已知的多种PLC同工酶中，PLCβ家族受异源三聚体G蛋白调节。本研究的目的是鉴定和表征人心肌中存在的PLCβ同工型。人心肌膜中的PLC活性依赖于Ca2+的存在。有趣的是，PLC被用作G蛋白激活剂的GTPγS显著刺激。这种刺激被GDP完全消除。然而，用作游离βγ亚基清除剂的视网膜转导素（α1）纯化α亚基并未消除这种效应，表明GTPγS刺激是由G蛋白α亚基介导的。PLC活性也受到从牛视网膜纯化的G蛋白βγ亚基（βγt）的刺激。加入纯化的αt可完全阻断这种刺激。逆转录和聚合酶链反应（RT-PCR）提供了证据，证明PLCβ1 mRNA在人心肌中表达，而未检测到与PLCβ2和PLCβ3 mRNA相对应的PCR产物。得出的结论是，PLCβ1 mRNA在人心肌中表达。人心肌PLC活性的功能特性与为PLCβ1确定的特性非常吻合，即对G蛋白α亚基以及βγ亚基敏感。然而，仍有可能存在其他尚未鉴定的PLC同工酶。鉴定人心肌中存在的PLCβ同工型并了解其受G蛋白亚基的调节，为研究该系统可能参与心肌肥大的病理生理学奠定了基础。
