Electrophysiological recordings and calcium measurements in striatal large aspiny interneurons in response to combined O2/glucose deprivation

Electrophysiological recordings and calcium measurements in striatal large aspiny interneurons in response to combined O-2/glucose deprivation. J. Neurophysiol. 81: 2508-2516, 1999. The effects of combined O-2/glucose deprivation were investigated on large aspiny (LA) interneurons recorded from a striatal slice preparation by means of simultaneous electrophysiological and optical recordings. LA interneurons were visually identified and impaled with sharp microelectrodes loaded with the calcium (Ca2+)-sensitive dye bis-fura-2. These cells showed the morphological, electrophysiological, and pharmacological features of large striatal cholinergic interneurons; O-2/glucose deprivation induced a membrane hyperpolarization coupled to a concomitant increase in intracellular Ca2+ concentration ([Ca2+](i)). Interestingly, this [Ca2+], elevation was more pronounced in dendritic branches rather than in the somatic region. The O-2/glucose-deprivation-induced membrane hyperpolarization reversed its polarity at the potassium (K+) equilibrium potential. Both membrane hyperpolarization and [Ca2+], rise were unaffected by TTX or by a combination of ionotropic glutamate receptors antagonists, D-2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione. Sulfonylurea glibenclamide, a blocker of ATP-sensitive K+ channels, markedly reduced the O-2 glucose-depdvation-induced membrane hyperpolarization but failed to prevent the rise in [Ca2+](i). Likewise, charybdotoxin, a large K+ channel(BK) inhibitor, abolished the membrane hyperpolarization but did not produce detectable changes of [Ca2+](i) elevation. A combination of high-voltage-activated Ca2+ channel blockers significantly reduced both the membrane hyperpolarization and the rise in [Ca2+],. In a set of experiments performed without dye in the recording electrode, either intracellular bis-(o-aminophenoxy)-N,N,N-1,N-1-tetraacetic acid or external barium abolished the membrane hyperpolarization induced by O-2/glucose deprivation. The hyperpolarizing effect on membrane potential was mimicked by oxotremorine, an M2-like muscarinic receptor agonist, and by baclofen, a GABA, receptor agonist. However, this membrane hyperpolarization was not coupled to an increase but rather to a decrease of the basal [Ca2+],. Furthermore glibenclamide did not reduce the oxotremorine- and baclofen-induced membrane hyperpolarization. In conclusion, the present results suggest that in striatal LA cells, O-2/glucose deprivation activates a membrane hyperpolarization that does not involve ligand-gated K+ conductances but is sensitive to barium, glibenclamide, and charybdotoxin. The increase in [Ca2+](i) is partially due to influx through voltage-gated high-voltage-activated Ca2+ channels.