title: Hyperglycemia reduces functional expression of astrocytic Kir4.1 channels and glial glutamate uptake.
abstract: Diabetics are at risk for a number of serious health complications including an increased incidence of epilepsy and poorer recovery after ischemic stroke. Astrocytes play a critical role in protecting neurons by maintaining extracellular homeostasis and preventing neurotoxicity through glutamate uptake and potassium buffering. These functions are aided by the presence of potassium channels, such as Kir4.1 inwardly rectifying potassium channels, in the membranes of astrocytic glial cells. The purpose of the present study was to determine if hyperglycemia alters Kir4.1 potassium channel expression and homeostatic functions of astrocytes. We used q-PCR, Western blot, patch-clamp electrophysiology studying voltage and potassium step responses and a colorimetric glutamate clearance assay to assess Kir4.1 channel levels and homeostatic functions of rat astrocytes grown in normal and high glucose conditions. We found that astrocytes grown in high glucose (25 mM) had an approximately 50% reduction in Kir4.1 mRNA and protein expression as compared with those grown in normal glucose (5mM). These reductions occurred within 4-7 days of exposure to hyperglycemia, whereas reversal occurred between 7 and 14 days after return to normal glucose. The decrease in functional Kir channels in the astrocytic membrane was confirmed using barium to block Kir channels. In the presence of 100-μM barium, the currents recorded from astrocytes in response to voltage steps were reduced by 45%. Furthermore, inward currents induced by stepping extracellular [K(+)]o from 3 to 10mM (reflecting potassium uptake) were 50% reduced in astrocytes grown in high glucose. In addition, glutamate clearance by astrocytes grown in high glucose was significantly impaired. Taken together, our results suggest that down-regulation of astrocytic Kir4.1 channels by elevated glucose may contribute to the underlying pathophysiology of diabetes-induced CNS disorders and contribute to the poor prognosis after stroke.
authors.affiliation: Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA. Electronic address: david.rivera11@upr.edu.
authors.forename: D E
authors.initials: DE
authors.lastname: Rivera-Aponte
authors.affiliation: Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA. Electronic address: miguel.mendez3@upr.edu.
authors.forename: M P
authors.initials: MP
authors.lastname: Méndez-González
authors.affiliation: Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA. Electronic address: aixafernanda@gmail.com.
authors.forename: A F
authors.initials: AF
authors.lastname: Rivera-Pagán
authors.affiliation: Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA. Electronic address: k_yurii@hotmail.com.
authors.forename: Y V
authors.initials: YV
authors.lastname: Kucheryavykh
authors.affiliation: Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA. Electronic address: kuc-lilia@mail.ru.
authors.forename: L Y
authors.initials: LY
authors.lastname: Kucheryavykh
authors.affiliation: Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA; Department of Physiology, Universidad Central del Caribe, Bayamón, PR, USA. Electronic address: sergueis64@gmail.com.
authors.forename: S N
authors.initials: SN
authors.lastname: Skatchkov
authors.affiliation: Department of Biochemistry, Universidad Central del Caribe, Bayamón, PR, USA. Electronic address: misty.eaton@uccaribe.edu.
authors.forename: M J
authors.initials: MJ
authors.lastname: Eaton
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D003124:Colorimetry; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects*; D005947:Glucose / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D019579:Neocortex / Q000166:cytology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013549:Sweetening Agents / Q000494:pharmacology*; D013997:Time Factors; D000098854:Kcnj10 Channel
chemical_list: D000098854:Kcnj10 Channel; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D013549:Sweetening Agents; D018698:Glutamic Acid; D005947:Glucose; D011188:Potassium
keywords: Kir4.1 potassium channels; astrocytes; diabetes; glutamate clearance; hyperglycemia