Application of near infra-red laser light increases current threshold in optic nerve consistent with increased Na < sup > + < /sup > -dependent transport

Pflugers Arch. 2024 Feb 29. doi: 10.1007/s00424-024-02932-1. Online ahead of print.ABSTRACTIncreases in the current threshold occur in optic nerve axons with the application of infra-red laser light, whose mechanism is only partly understood. In isolated rat optic nerve, laser light was applied near the site of electrical stimulation, via a flexible fibre optic. Paired applications of light produced increases in threshold that were reduced on the second application, the response recovering with increasing delays, with a time constant of 24 s. 3-min duration single applications of laser light gave rise to a rapid increase in threshold followed by a fade, whose time-constant was between 40 and 50 s. After-effects were sometimes apparent following the light application, where the resting threshold was reduced. The increase in threshold was partially blocked by 38.6 mM Li+ in combination with 5 μ M bumetanide, a manoeuvre increasing refractoriness and consistent with axonal depolarization. Assessing the effect of laser light on the nerve input resistance ruled out a previously suggested fall in myelin resistance as contributing to threshold changes. These data appear consistent with an axonal membrane potential that partly relies on temperature-dependent electroneutral Na+ influx, and where fade in the response to the laser may be caused by a gradually diminishing Na+ pump-induced hyperpolarization, in response to falling intracellular [Na+].PMID:38421407 | DOI:10.1007/s00424-02...

Source: Pflugers Archiv : European Journal of Physiology - February 29, 2024 Category: Physiology Authors: Hin Heng Lo Tawan Munkongcharoen Rosa M Muijen Ritika Gurung Anjali G Umredkar Mark D Baker Source Type: research