Metabolic stress as a contributor to physiological opening of TRP channels in blowfly (Calliphora vicina)

Abstract

Abstract Purpose: TRP channels in blowflies can be reversibly activated by metabolic stress. Activation can be caused by hypoxia or mitochondrial uncoupling and results in membrane depolarization. The changes where traced as changes in extracellular ionic composition, photoreceptor membrane currents and changes in membrane potential. Idea of specific signaling pathway opening TRP channels was rejected with findings that impairment of PIP2 under lack of ATP, results in activation of TRP channels. Even though the mechanism of metabolic stress TRP channel activation is elucidated, it remained unanswered what rate of metabolic stress is needed to open the channels and whether under physiological conditions photoreceptor cells encounter the rate of metabolic stress that can significantly contribute to opening of TRP channels. Methods: Extracellular concentrations of [K+]o, [Na+]o and [Ca2+]o were measured using the ion‐selective microelectrodes. The redox states of respiratory pigments (flavoproteins and cytochromes) in the eyes of blowflies (Calliphora vicina) were measured with time‐resolved absorption spectroscopy and use of principal components analysis. Anoxia was reached in under 2s time. Results: Changes in [K+]o, [Na+]o and [Ca2+]o appeared with latency of 8.06 ± 1.38 s, 10.38 ± 2.48 s and 13.11 ± 3.09 s, respectively (mean ± s.e.m., n=7). First detectable changes in redox state of cytochrome c respiratory pigment started at 1.79 ± 0.19 s and reached 39.4% ± 5.4 % of the maximal reduction by the time changes in ionic composition were detectable. Conclusions: Our conclusion was that high degree of maximal redox state change is needed (39.4%) to open TRP channels, what is unlikely to happen under physiological conditions.