Angiotensin type 2 receptor neuroprotection against chemical hypoxia is dependent on the delayed rectifier K+ channel, Na+/Ca2+ exchanger and Na+/K+ ATPase in primary cortical cultures

We have previously reported that angiotensin 11 (Ang 11) protects cortical neurons from chemical-induced hypoxia through activation of the angiotensin type 2 (AT,) receptor. Here, we show in mouse primary neuronal cultures that the AT(2) receptor neuroprotection results from the activation of the delayed rectifier K+ channel as well as the involvement of the Na+/Ca2+ exchanger (NCX) and Na+/K+ ATPase (ATPase). Roles of the K+ channel. NCX and ATPase were determined using the specific blockers a-dendrotoxin, KB-R7943 and ouabain, respectively. Sodium azide (10 mM) induced apoptosis in 40% of neurons. Inhibition of the AT, receptor with losartan (I muM) facilitated angiotensin 11 mediated neuroprotection by reducing sodium azide-induced apoptosis 61.8 +/- 5.6%, while inhibition of the AT(2) receptor with PD123319 (1 muM) showed no neuroprotection. These results suggest that angiotensin 11 neuroprotection is mediated through the AT(2) receptor and requires inhibition of the AT, receptor in order to facilitate its effect. To determine the roles of delayed rectifier K+ channel, NCX and ATPase cultures were pretreated with alpha-dendrotoxin (10 nM), KB-R7943 (100 nM) and ouabain (100 nM), which significantly attenuated AT(2) receptor mediated neuroprotection. These findings further suggest that the mechanism of AT(2) receptor mediated neuroprotection is coupled to activation of the delayed rectifier K+ channel, NCX and ATPase. (C) 2004 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.