OBJECTIVE: Short infrared (IR) laser pulses have been used to stimulate action potentials in neurons both in vivo and in vitro. However, the mechanism(s) underlying this phenomenon has remained elusive. In vitro studies have found that pulsed IR exposure generates a nearly instant change in capacitance in the plasma membrane, characterized by inward rectification, a common feature in pore-forming exposures, such as electrical pulses and acoustic shock waves. Based on this similarity, we hypothesize that the mechanism of IR stimulation is the formation of short-lived nanopores in the plasma membrane. These transient, small-diameter pores allow the influx of extracellular ions that lead to action potential generation, possibly through activation of secondary messenger pathways or depolarization of the cell membrane resulting in activation of voltage-gated ion channels. APPROACH: A variety of fluorescent markers are used to observe the cell response to IR stimulation to monitor for effects indicative of nanoporation in other modalities. MAIN RESULTS: We observe rapid, transient rises in intracellular Ca(2+), influx of YO-PRO-1 and propidium iodide into the cell signifying membrane permeabilization, cellular blebbing and swelling, and activation of the intracellular phosphoinositides lipid signaling pathway. SIGNIFICANCE: This conclusion better explains the experimental observations and limitations of IR-induced neurological stimulation and represents a distinct theoretical shift in the understanding of the mechanism of IR-induced stimulation.
OBJECTIVE: Short infrared (IR) laser pulses have been used to stimulate action potentials in neurons both in vivo and in vitro. However, the mechanism(s) underlying this phenomenon has remained elusive. In vitro studies have found that pulsed IR exposure generates a nearly instant change in capacitance in the plasma membrane, characterized by inward rectification, a common feature in pore-forming exposures, such as electrical pulses and acoustic shock waves. Based on this similarity, we hypothesize that the mechanism of IR stimulation is the formation of short-lived nanopores in the plasma membrane. These transient, small-diameter pores allow the influx of extracellular ions that lead to action potential generation, possibly through activation of secondary messenger pathways or depolarization of the cell membrane resulting in activation of voltage-gated ion channels. APPROACH: A variety of fluorescent markers are used to observe the cell response to IR stimulation to monitor for effects indicative of nanoporation in other modalities. MAIN RESULTS: We observe rapid, transient rises in intracellular Ca(2+), influx of YO-PRO-1 and propidium iodide into the cell signifying membrane permeabilization, cellular blebbing and swelling, and activation of the intracellular phosphoinositides lipid signaling pathway. SIGNIFICANCE: This conclusion better explains the experimental observations and limitations of IR-induced neurological stimulation and represents a distinct theoretical shift in the understanding of the mechanism of IR-induced stimulation.
Authors: William G A Brown; Karina Needham; James M Begeng; Alexander C Thompson; Bryony A Nayagam; Tatiana Kameneva; Paul R Stoddart Journal: Biomed Opt Express Date: 2020-03-27 Impact factor: 3.732