Lu C, Zhang D Q, McMahon D G
Department of Physiology, University of Kentucky, Lexington 40536-0084, USA.
Vis Neurosci. 1999 Sep-Oct;16(5):811-8. doi: 10.1017/s0952523899165015.
Electrical coupling between H2 horizontal cell pairs isolated from the hybrid bass retina was studied using dual whole-cell, voltage-clamp technique. Voltage-dependent inactivation of junctional currents in response to steps in transjunctional voltage (Vj) over a range of +/-100 mV was characterized for 89 cell pairs. Approximately one-quarter of the pairs exhibited strongly voltage-dependent junctions (>50% reduction in junctional current at +/-100 mV), another quarter of the pairs exhibited voltage-independent junctional current (<5% reduction at +/-100 mV), and the remainder of the pairs exhibited intermediate values for voltage inactivation. We focused on further characterizing the Vj-independent junctions of horizontal cells, which have not been described previously in detail. When Lucifer Yellow dye was included in one recording pipette, pairs exhibiting Vj-independent coupling showed no (9/12), or limited (3/12), passage of dye. Vj-independent coupling was markedly less sensitive to the modulators SNP (100-300 microM, -9% reduction in coupling) and dopamine (100-300 microM, -6%) than were Vj-dependent junctions (-45% and -44%). However, simultaneous application of both SNP and dopamine significantly reduced Vj-independent coupling (-56%). Both Vj-independent and Vj-dependent junctions were blocked by DMSO (1-2%), but Vj-independent junctions were not blocked by heptanol. Single-channel junctional conductances of Vj-independent junctions range from 112-180 pS, versus 50-60 pS for Vj-dependent junctions. The results reveal that Vj-independent coupling in a subpopulation of horizontal cells from the hybrid bass retina is mediated by cellular junctions with physiological and pharmacological characteristics distinct from those previously described in fish horizontal cells.
利用双全细胞电压钳技术研究了从杂交鲈鱼视网膜分离出的H2水平细胞对之间的电耦合。对89个细胞对的跨结电压（Vj）在±100 mV范围内阶跃时，连接电流的电压依赖性失活进行了表征。大约四分之一的细胞对表现出强烈的电压依赖性连接（在±100 mV时连接电流降低>50%），另外四分之一的细胞对表现出电压非依赖性连接电流（在±100 mV时降低<5%），其余细胞对表现出电压失活的中间值。我们专注于进一步表征水平细胞的Vj非依赖性连接，此前尚未对其进行详细描述。当在一个记录微管中加入荧光黄染料时，表现出Vj非依赖性耦合的细胞对没有（9/12）或仅有有限的（3/12）染料通过。与Vj依赖性连接（分别降低-45%和-44%）相比，Vj非依赖性耦合对调节剂SNP（100 - 300 μM，耦合降低-9%）和多巴胺（100 - 300 μM，降低-6%）的敏感性明显较低。然而，同时应用SNP和多巴胺会显著降低Vj非依赖性耦合（-56%）。Vj非依赖性和Vj依赖性连接都被DMSO（1 - 2%）阻断，但Vj非依赖性连接不被庚醇阻断。Vj非依赖性连接的单通道连接电导范围为112 - 180 pS，而Vj依赖性连接为50 - 60 pS。结果表明，杂交鲈鱼视网膜水平细胞亚群中的Vj非依赖性耦合是由细胞连接介导的，其生理和药理学特性与鱼类水平细胞中先前描述的不同。
