Figure 1.

Depolarization preconditioning protects against hypoxia. A. Schematic of preconditioning/hypoxic exposure paradigm. B. Photomicrographs from a single experiment demonstrating depolarization protection. Upper left: brightfield image from a normoxic control stained with trypan blue 24 hr post-preconditioning with 4 hr of 30 mM NaCl (control preconditioning) and 2.5 hr sham hypoxia. Upper right: A field from a dish preconditioned with 30 mM NaCl and subjected to 2.5 hr hypoxia. Trypan blue positive pyknotic nuclei are apparent. Lower left: a field from a dish preconditioned with 30 mM KCl for 4 hr and then subjected to 2.5 hr hypoxia. Lower right: a protection control in which 1 μM NBQX and 100 μM D-APV, ionotropic glutamate receptor (GluR) antagonists, were included in the hypoxia media. C. Summary of experiments like that depicted in panel B, showing protection afforded by KCl depolarization preconditioning. Cell survival is expressed as the percentage of trypan blue negative cells averaged over ten fields evaluated with a 20x objective (n=7 independent experiments). Asterisks designate p < 0.05 compared with NaCl hypoxia (unpaired, two-tailed t-tests with Bonferroni correction for multiple comparisons). Gray bar emphasizes the major hypothesized result of KCl preconditioning protection.