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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Role of transporters and ion channels in neuronal injury under hypoxia

Departments of ¹Pediatrics and ²Neuroscience, University of California San Diego, La Jolla; and ³The Rady Children's Hospital, San Diego, California

Submitted 23 July 2007 ; accepted in final form 25 October 2007

The aims of the current study were to 1) examine the effects of hypoxia and acidosis on cultured cortical neurons and 2) explore the role of transporters and ion channels in hypoxic injury. Cell injury was measured in cultured neurons or hippocampal slices following hypoxia (1% O₂) or acidosis (medium pH 6.8) treatment. Inhibitors of transporters and ion channels were employed to investigate their roles in hypoxic injury. Our results showed that 1) neuronal damage was apparent at 5–7 days of hypoxia exposure, i.e., 36–41% of total lactate dehydrogenase was released to medium and 2) acidosis alone did not lead to significant injury compared with nonacidic, normoxic controls. Pharmacological studies revealed 1) no significant difference in neuronal injury between controls (no inhibitor) and inhibition of Na⁺-K⁺-ATP pump, voltage-gated Na⁺ channel, ATP-sensitive K⁺ channel, or reverse mode of Na⁺/Ca²⁺ exchanger under hypoxia; however, 2) inhibition of NBCs with 500 µM DIDS did not cause hypoxic death in either cultured cortical neurons or hippocampal slices; 3) in contrast, inhibition of Na⁺/H⁺ exchanger isoform 1 (NHE1) with either 10 µM HOE-642 or 2 µM T-162559 resulted in dramatic hypoxic injury (+95% for HOE-642 and +100% for T-162559 relative to normoxic control, P < 0.001) on treatment day 3, when no death occurred for hypoxic controls (no inhibitor). No further damage was observed by NHE1 inhibition on treatment day 5. We conclude that inhibition of NHE1 accelerates hypoxia-induced neuronal damage. In contrast, DIDS rescues neuronal death under hypoxia. Hence, DIDS-sensitive mechanism may be a potential therapeutic target.

sodium/hydrogen exchanger 1; HCO₃^– transporters; disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate; neuronal protection