Wiedmann R T, Tan R C, Joyner R W
Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Am J Physiol. 1996 Oct;271(4 Pt 2):H1507-16. doi: 10.1152/ajpheart.1996.271.4.H1507.
Conduction through the cardiac syncytium varies from being nearly continuous, with very well coupled cells, to being clearly discontinuous, with significant conduction delays over very short distances. The Purkinje-ventricular muscle junction (PVJ) sites on the endocardial surface have characteristic delays of conduction and the presence of discrete groups of cells that suggest significant discontinuities of the conduction process at PVJ sites, as compared with the more nearly continuous conduction within either the Purkinje or the ventricular muscle layers of the papillary muscle. The purpose of the present study was to examine the relative sensitivity of conduction at PVJ sites versus conduction within the Purkinje or the ventricular muscle layer of the canine papillary muscle to agents that modulate L-type calcium current. We have used cadmium as a relatively specific blocker of L-type calcium current and isoproterenol as an agent to increase L-type calcium current to test the hypothesis that discontinuous conduction at the PVJ sites would be more sensitive to these agents than would continuous conduction within either the Purkinje layer or the ventricular muscle layer of a canine papillary muscle. Conduction delay at the PVJ sites was significantly increased by cadmium, with some PVJ sites reversibly becoming nonjunctional at 200-400 microM cadmium. Isoproterenol significantly decreased PVJ delay, and this effect was attenuated by carbachol. All of the effects on conduction delay at the PVJ sites were much greater than the effects for the same agents on conduction velocity within either the Purkinje or the ventricular muscle layer of the papillary muscle.
通过心脏肌纤维网的传导情况各不相同，从细胞耦合良好时几乎连续，到明显不连续，在很短距离内就存在显著的传导延迟。心内膜表面的浦肯野 - 心室肌连接（PVJ）部位具有特征性的传导延迟，并且存在离散的细胞群，这表明与乳头肌的浦肯野层或心室肌层内更接近连续的传导相比，PVJ部位的传导过程存在显著的不连续性。本研究的目的是检验PVJ部位的传导相对于犬乳头肌的浦肯野层或心室肌层内的传导对调节L型钙电流的药物的相对敏感性。我们使用镉作为L型钙电流的相对特异性阻滞剂，异丙肾上腺素作为增加L型钙电流的药物，以检验以下假设：PVJ部位的不连续传导对这些药物的敏感性高于犬乳头肌的浦肯野层或心室肌层内的连续传导。镉显著增加了PVJ部位的传导延迟，在200 - 400微摩尔镉浓度下，一些PVJ部位可逆地变为非连接状态。异丙肾上腺素显著降低了PVJ延迟，并且这种作用被卡巴胆碱减弱。所有对PVJ部位传导延迟的影响都远大于相同药物对乳头肌的浦肯野层或心室肌层内传导速度的影响。
