Local anesthetic lidocaine decelerates cytoplasmic streaming in Egeria densa via altered actin dynamics and reactive oxygen species generation

Local anesthetics (LAs) block voltage-gated Na+ channels in mammals, but they also affect cytoplasmic streaming in plant cells. Although certain LAs inhibit streaming in algae such as Chara, the underlying mechanisms remain unclear. This study aimed to elucidate how LAs reduce cytoplasmic streaming velocity, focusing on the actomyosin system and oxidative stress responses, using lidocaine as a representative LA. Streaming velocity in Egeria densa leaves decreased reversibly after lidocaine treatment and recovered following a washout procedure. Confocal laser scanning microscopy of fluorescently stained actin filaments revealed that lidocaine disrupted F-actin structures. Electron spin resonance analysis showed that lidocaine induced reactive oxygen species (ROS) production in a dose-dependent manner, and spatiotemporal fluorescence analysis with ROS-sensitive probes demonstrated that ROS accumulated near the plasma membrane and increased over time; this process appeared to be mediated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and Ca2+ influx. Application of antioxidants attenuated the lidocaine-induced reduction in streaming velocity. In conclusion, lidocaine slows cytoplasmic streaming in E. densa by eliciting a reversible, multifaceted response involving NADPH oxidase–derived ROS, Ca2+ influx, and actomyosin remodeling, offering mechanistic insight into the still poorly understood phenomenon of local anesthetic action in plants.