Transient acidosis induces a preconditioning chloride conductance that protects mouse nodose neurons from NMDA‐induced apoptosis (1132.13)

Abstract

Glutamate is a primary neurotransmitter expressed in nodose ganglia where the soma of baroreceptor and vagal afferent neurons are located. Excessive N‐methyl‐D‐aspartate (NMDA) receptor activation by glutamate initiates excitotoxicity and may cause nodose neuronal damage and apoptosis. In previous studies we showed that brief exposure to low pH induces activation of a novel prolonged Cl‐ conductance in nodose neurons. A similar Cl‐ conductance has been shown in cardiac myocytes to be protective from ischemic reperfusion damage (Diaz et al. 1999) . Here we tested the hypothesis that vagal sensory neurons may be protected from NMDA induced excitotoxicity and apoptosis by low pHo preconditioning.Nodose neurons of 3 months old mice were cultured and exposed to 3 brief pulses of low pH (6.0) solution each lasting 15 seconds with intervals of 10 seconds. After 20 minutes, 50 μM NMDA plus 10 μM Glycine (NMDA receptor co‐activator) were added to the cultures. Apoptotic nodose neurons were fluorescently detected by using Alexa Fluor 488 annexin V. Without preconditioning acidosis, the increases in apoptotic neurons as percentages of viable neurons during exposures to NMDA for 20, 40 and 60 minutes were 16 ± 1 (n=2346), 33 ± 4 (n=2056) and 40 ± 8% (n=2093) (p<0.01). After preconditioning acidosis at pH6.0 the increases in NMDA‐induced neuronal apoptosis became less, with levels of 6 ± 2% (n=1764), 10 ± 3% (n=1438) and 16 ± 3% (n=1678) of the total viable neurons. This pHo preconditioning effect was restored partially by 10 μM Tamoxifen, a non‐specific Cl‐ channel blocker, resulting in apoptosis levels of 12 ± 3% (n=831), 22 ± 2% (n=858) and 27 ± 2% (n=804). Thus a transient preconditioning Cl‐ conductance activated by low pHo reduced significantly the NMDA‐induced neuronal damage ( ANOVA, p<0.01). This work provides a putative molecular ionic basis for a neuronal protection during ischemic damage.Grant Funding Source: Supported by NIH with HL14388