Within only 2-3 min of brain ischemia, extracellular K+ concentrations ([K+])o reach 60 - 80 mM, which implies that the excitotoxic action of glutamate during ischemia is executed at highly elevated [K+]o. The proposed research will study whether such high [K+]o affects mechanisms of glutamate excitotoxicity. The hypothesis """"""""High [K+]o reduces the electrochemical Ca2+ driving force (ECDF) in neurons exposed to glutamate receptor agonists"""""""" will be tested in Aim 1: """"""""Study the effects of various [K+]o on the plasma membrane potential (Em) and the cytoplasmic Ca2+ concentration ([Ca2+]c) in cultured cortical and cerebellar neurons exposed to glutamate receptor agonists"""""""". To this end, neurons will be loaded with Em- and Ca2+-sensitive fluorescent probes. This hypothesis, if true, predicts that high [K+]o may prevent excitotoxicity by decreasing the glutamate mediated Ca2+ influx across the plasma membrane. It is also possible, however, that glutamate may collapse the Na+ and K+ concentration gradients across the plasma membrane and, consequently, set Em close to zero regardless of [K+]o. To test whether this is the case, the cytoplasmic Na+ and K+ concentrations will be measured in parallel experiments in neurons loaded with Na+- and K+-sensitive fluorescent probes. An alternative hypothesis, will be tested in Aim 2: """"""""Determine whether increasing [K+]o may inhibit the glutamate-mediated Ca2+ influx in a manner not related to the plasma membrane depolarization"""""""". To this end, the effects of [K+]o on Ca2+ accumulation stimulated by glutamate receptor agonists will be studied in neurons depolarized by a Na+ and K+ ionophore, gramicidin. Finally, in Aim 3: """"""""Test whether restoration of low [K+]o following ischemia in vitro causes a delayed Ca2+ accumulation and compromises neuronal survival"""""""", it will be studied whether [K+]o during the postischemic period affects Ca2+ homeostasis and is related to improved or compromised neuronal survival during the next 24 hours. These studies may yield a new target for pharmacological intervention to decrease neuronal death following ischemia or hypoglycemia, namely, to prevent excessive K+ loss from the brain during reperfusion.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
5R29NS037390-02
Application #
6139561
Study Section
Special Emphasis Panel (ZRG1-BDCN-3 (01))
Program Officer
Behar, Toby
Project Start
1999-01-01
Project End
2003-12-31
Budget Start
2000-01-01
Budget End
2000-12-31
Support Year
2
Fiscal Year
2000
Total Cost
$103,711
Indirect Cost
Name
University of Illinois at Chicago
Department
Psychiatry
Type
Schools of Medicine
DUNS #
121911077
City
Chicago
State
IL
Country
United States
Zip Code
60612