Medical and Biological Physics, Department of Physics, Technical University Dortmund, Otto-Hahn-Str. 4, 44227 Dortmund, Germany.
Biochim Biophys Acta Biomembr. 2023 Jan 1;1865(1):184073. doi: 10.1016/j.bbamem.2022.184073. Epub 2022 Oct 12.
Ever since the pioneering studies in the 1960s and 70s, the importance of order transitions for cell membrane functions has remained a matter of debate. Recently, it has been proposed that the nonlinear stimulus-response curve of excitable cells, which manifests in all-or-none pulses (action potentials (AP)), is due to a transition in the cell membrane. Indeed, evidence for transitions has accumulated in plant cells and neurons, but studies with other excitable cells are expedient in order to show if this finding is of a general nature. Herein, we investigated intact, motile specimens of the "swimming neuron" Paramecium. The cellular membranes were labelled with the solvatochromic fluorophores LAURDAN or Di-4-ANEPPDHQ. Subsequently, a cell was trapped in a microfluidic channel and investigated by fluorescence spectroscopy. The generalized polarization (GP) of the fluorescence emission from cell cortical membranes (probably plasma and alveolar membranes) was extracted by an edge-finding algorithm. The thermo-optical state diagram, i.e. the dependence of GP on temperature, exhibited clear indications for a reversible transition. This transition had a width of ~10-15 °C and a midpoint that was located ~4 °C below the growth temperature. The state diagrams with LAURDAN and Di-4-ANEPPDHQ had widely identical characteristics. These results suggested that the cortical membranes of Paramecium reside in an order transition regime under physiological growth conditions. Based on these findings, membrane potential fluctuations, spontaneous depolarizing spikes, and thermal excitation of Paramecium was interpreted.
自 20 世纪 60 年代和 70 年代的开创性研究以来，细胞膜功能的有序转变的重要性一直存在争议。最近，有人提出，可兴奋细胞的非线性刺激-反应曲线，表现在全有或全无脉冲（动作电位 (AP)）中，是由于细胞膜的转变。事实上，在植物细胞和神经元中已经积累了证据表明存在转变，但进行其他可兴奋细胞的研究是很有必要的，以证明这一发现是否具有普遍性。在此，我们研究了“游动神经元”草履虫的完整、能动标本。细胞膜用溶剂化变色荧光染料 LAURDAN 或 Di-4-ANEPPDHQ 标记。随后，将一个细胞困在微流控通道中，并通过荧光光谱法进行研究。通过边缘检测算法提取细胞皮质膜（可能是质膜和肺泡膜）的荧光发射的广义极化（GP）。热光学状态图，即 GP 对温度的依赖性，清楚地表明存在可逆转变。该转变的宽度约为 10-15°C，中点位于生长温度以下约 4°C。LAURDAN 和 Di-4-ANEPPDHQ 的状态图具有广泛相同的特征。这些结果表明，在生理生长条件下，草履虫的皮质膜处于有序转变状态。基于这些发现，对草履虫的膜电位波动、自发去极化尖峰和热激发进行了解释。
