Beilby M J, Bisson M A
Biophysics Department, School of Physics, University of New South Wales, Sydney 2052, Australia.
J Membr Biol. 1999 Sep 1;171(1):63-73. doi: 10.1007/s002329900559.
The current-voltage (I/V) profiles of Ventricaria (formerly Valonia) membranes were measured at a range of external potassium concentrations, K(+), from 0.1 to 100 mm. The conductance-voltage (G/V) characteristics were computed to facilitate better resolution of the profile change with time after exposure to different K(+). The resistance-voltage (R/V) characteristics were computed to attempt resolution of plasmalemma and tonoplast. Four basic electrophysiological stages emerged: (1) Uniform low resistance between -60 and +60 mV after the cell impalement. (2) High resistance between +50 and +150 for K(+) from 0.1 to 1.0 mm and hypotonic media. (3) High resistance between -150 and -20 mV for K(+) of 10 mm (close to natural seawater) and hypertonic media. (4) High resistance between -150 and +170 mV at K(+) of 100 mm. The changes between these states were slow, requiring minutes to hours and sometimes exhibiting spontaneous oscillations of the membrane p.d. (potential difference). Our analysis of the I/V data supports a previous hypothesis, that Ventricaria tonoplast is the more resistive membrane containing a pump, which transports K(+) into the vacuole to regulate turgor. We associate state (1) with the plasmalemma conductance being dominant and the K(+) pump at the tonoplast short-circuited probably by a K(+) channel, state (2) with the K(+) pump "off" or short-circuited at p.d.s more negative than +50 mV, state (3) with the K(+) pump "on, " and state (4) with the pump dominant, but affected by high K(+). A model for the Ventricaria membrane system is proposed.
在一系列外部钾离子浓度K⁺（从0.1到100 mM）下测量了海仙人掌（原伞藻属）细胞膜的电流-电压（I/V）曲线。计算了电导-电压（G/V）特性，以便更好地解析暴露于不同K⁺后随时间变化的曲线变化。计算了电阻-电压（R/V）特性，以尝试分辨质膜和液泡膜。出现了四个基本的电生理阶段：(1) 细胞穿刺后在-60至+60 mV之间呈现均匀的低电阻。(2) 对于K⁺从0.1到1.0 mM的情况以及低渗介质，在+50至+150之间呈现高电阻。(3) 对于10 mM的K⁺（接近天然海水）以及高渗介质，在-150至-20 mV之间呈现高电阻。(4) 在100 mM的K⁺时，在-150至+170 mV之间呈现高电阻。这些状态之间的变化很缓慢，需要数分钟到数小时，有时还会出现膜电位差（电势差）的自发振荡。我们对I/V数据的分析支持了先前的一个假设，即海仙人掌液泡膜是电阻更大的膜，含有一个将K⁺转运到液泡中以调节膨压的泵。我们将状态(1)与质膜电导占主导且液泡膜上的K⁺泵可能被一个K⁺通道短路相关联，状态(2)与K⁺泵“关闭”或在电势差比+50 mV更负时被短路相关联，状态(3)与K⁺泵“开启”相关联，状态(4)与泵占主导但受高K⁺影响相关联。提出了一个海仙人掌膜系统的模型。
