Electrophysiological recordings and calcium measurements in striatal largeaspiny interneurons in response to combined O-2/glucose deprivation

Electrophysiological recordings and calcium measurements in striatal large aspiny interneurons in response to combined O-2/glucose deprivation. J. Neu rophysiol. 81: 2508-2516, 1999. The effects of combined O-2/glucose depriva tion were investigated on large aspiny (LA) interneurons recorded from a st riatal slice preparation by means of simultaneous electrophysiological and optical recordings. LA interneurons were visually identified and impaled wi th sharp microelectrodes loaded with the calcium (Ca2+)-sensitive dye bis-f ura-2. These cells showed the morphological, electrophysiological, and phar macological features of large striatal cholinergic interneurons; O-2/glucos e deprivation induced a membrane hyperpolarization coupled to a concomitant increase in intracellular Ca2+ concentration ([Ca2+](i)). Interestingly, t his [Ca2+], elevation was more pronounced in dendritic branches rather than in the somatic region. The O-2/glucose-deprivation-induced membrane hyperp olarization reversed its polarity at the potassium (K+) equilibrium potenti al. Both membrane hyperpolarization and [Ca2+], rise were unaffected by TTX or by a combination of ionotropic glutamate receptors antagonists, D-2-ami no-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione. Sulfon ylurea glibenclamide, a blocker of ATP-sensitive K+ channels, markedly redu ced the O-2 glucose-depdvation-induced membrane hyperpolarization but faile d to prevent the rise in [Ca2+](i). Likewise, charybdotoxin, a large K+ cha nnel(BK) inhibitor, abolished the membrane hyperpolarization but did not pr oduce detectable changes of [Ca2+](i) elevation. A combination of high-volt age-activated Ca2+ channel blockers significantly reduced both the membrane hyperpolarization and the rise in [Ca2+],. In a set of experiments perform ed without dye in the recording electrode, either intracellular bis-(o-amin ophenoxy)-N,N,N-1,N-1-tetraacetic acid or external barium abolished the mem brane hyperpolarization induced by O-2/glucose deprivation. The hyperpolari zing effect on membrane potential was mimicked by oxotremorine, an M2-like muscarinic receptor agonist, and by baclofen, a GABA, receptor agonist. How ever, this membrane hyperpolarization was not coupled to an increase but ra ther to a decrease of the basal [Ca2+],. Furthermore glibenclamide did not reduce the oxotremorine- and baclofen-induced membrane hyperpolarization. I n conclusion, the present results suggest that in striatal LA cells, O-2/gl ucose deprivation activates a membrane hyperpolarization that does not invo lve ligand-gated K+ conductances but is sensitive to barium, glibenclamide, and charybdotoxin. The increase in [Ca2+](i) is partially due to influx th rough voltage-gated high-voltage-activated Ca2+ channels.