Li X, Simard J M
Departments of Neurosurgery and Physiology, University of Maryland School of Medicine, Baltimore, MD, USA.
Circ Res. 1999 Jun 11;84(11):1277-84. doi: 10.1161/01.res.84.11.1277.
Three connexins, Cx43, Cx40, and Cx37, have been found by protein or mRNA analysis to be prominent in mammalian blood vessels, but electrophysiological characterization of gap junction channels in freshly isolated vascular smooth muscle cells (SMCs) has not previously been reported. We used a dual-perforated patch-clamp technique to study gap junction conductances in SMC pairs from rat basilar arteries. Macroscopic junctional conductance (Gj) measured in 98 cell pairs with either Cs+ or K+ ranged between 0.68 and 24.8 nS. In weakly coupled cells (Gj<5 nS), single-channel currents were readily resolved without pharmacological uncoupling agents, allowing identification of 4 major unitary conductances. Two of these conductances, 80 to 120 pS and 150 to 200 pS, corresponded to the major conductance states for homotypic channels formed from Cx43 or Cx40, which we confirmed were present in smooth muscle by immunofluorescence analysis. Two other conductances, 220 to 280 pS and >300 pS, were identified that have not been previously reported in vascular SMCs. Macroscopic recordings revealed currents that deactivated incompletely over a broad range of transjunctional potentials. In about half of the pairs, we identified macroscopic as well as single-channel currents that exhibited marked voltage asymmetry, consistent with nonhomotypic, ie, either heterotypic or heteromeric channels. Our data indicate that basilar artery SMCs are coupled in vivo in a richly complex manner, involving Cx43, Cx40, and other large-conductance channels, and that a significant number of couplings involve putative nonhomotypic channels.
通过蛋白质或mRNA分析发现，三种连接蛋白Cx43、Cx40和Cx37在哺乳动物血管中含量丰富，但此前尚未报道过对新鲜分离的血管平滑肌细胞（SMC）中缝隙连接通道的电生理特性研究。我们使用双穿孔膜片钳技术研究大鼠基底动脉SMC对中的缝隙连接电导。在98个细胞对中，用Cs⁺或K⁺测量的宏观连接电导（Gj）范围为0.68至24.8 nS。在弱耦合细胞（Gj<5 nS）中，无需药理学解偶联剂即可轻松分辨单通道电流，从而识别出4种主要的单位电导。其中两种电导，80至120 pS和150至200 pS，对应于由Cx43或Cx40形成的同型通道的主要电导状态，我们通过免疫荧光分析证实其存在于平滑肌中。另外两种电导，220至280 pS和>300 pS，此前尚未在血管SMC中报道过。宏观记录显示，电流在很宽的跨连接电位范围内不完全失活。在大约一半的细胞对中，我们识别出宏观电流以及单通道电流，它们表现出明显的电压不对称，这与非同型通道（即异型或异聚体通道）一致。我们的数据表明，基底动脉SMC在体内以高度复杂的方式耦合，涉及Cx⁴³、Cx⁴⁰和其他大电导通道，并且大量耦合涉及假定的非同型通道。
