The protective action of tetrodotoxin and (±)-Kavain on anaerobic glycolysis, ATP content and intracellular Na+ and Ca2+ of anoxic brain vesicles

• Published in: Neuropharmacology Vol. 35; no. 12; pp. 1743 - 1752
• Main Authors: GLEITZ, J, TOSCH, C, BEILE, A, PETERS, T
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier 1996
• Subjects: Adenosine Triphosphate - metabolism; Anaerobiosis; Animals; Anticonvulsants - pharmacology; Benzofurans; Biological and medical sciences; Brain - drug effects; Brain - metabolism; Brain Ischemia - metabolism; Calcium - metabolism; Ethers, Cyclic; Fluorescent Dyes; Fura-2; Glycolysis - drug effects; Hypoxia, Brain - metabolism; Kinetics; Lactates - metabolism; Male; Medical sciences; NAD - metabolism; Neuropharmacology; Neuroprotective agent; Oxygen Consumption; Pharmacology. Drug treatments; Pyrones - pharmacology; Rats; Rats, Wistar; Sodium - metabolism; Sodium Channel Blockers; Tetrodotoxin - pharmacology; Anoxia; Rat; Rodentia; Central nervous system; Piperaceae; Ionic channel; Neuroprotective agent; In vitro; Prevention; Vertebrata; Mammalia; Calcium ion; Dicotyledones; Animal; Angiospermae; Sodium ion; Glycolysis; Spermatophyta; Antagonist; Mechanism of action; ATP; Brain (vertebrata)
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/S0028-3908(96)00106-2

Because recent reports point to Na+ channel blockers as protective agents directed against anoxia-induced neuronal damage including protection of anaerobic glycolysis, the influences of tetrodotoxin (TTX) and (+/-)-kavain on anoxic rat brain vesicles were investigated with respect to lactate synthesis, vesicular ATP content and cytosolic free Na+ and Ca2+ ([Na+]i, [Ca2+]i), both of the latter determined fluorometrically employing SBFI and FURA-2, respectively. After anoxia, basal lactate production was increased from 2.9 to 9.8 nmol lactate/min/mg protein. Although lactate synthesis seemed to be stable for at least 45 min of anoxia, as deduced from the linearity of lactate production, the ATP content declined continuously with a half life (tau 1/2) of 14.5 min, indicating that anaerobic glycolysis was insufficient to cover the energy demand of anoxic vesicles. Correspondingly, [Na+]i and [Ca2+]i increased persistently after anoxia by 22.1 mmol/l Na+ and 274.9 nmol/l Ca2+, determined 6.3 min after onset. An additional stimulation of vesicles with veratridine accelerated the drop of ATP (tau 1/2 = 5.1 min) and provoked a massive Na+ overload, which levelled off to 119 mmol/l Na+ within a few minutes. Concomitantly, [Ca2+]i increased linearly with a rate of 355 nmol Ca2+/l/min. Despite the massive perturbation of ion homeostasis, lactate production was unaffected during the first 8 min of veratridine stimulation. However, complete inhibition of lactate synthesis took place 30 min after veratridine was added. The Na+ channel blockers TTX and (+/-)-kavain, if applied before anoxia, preserved vesicular ATP content, diminished anoxia-induced increases in [Na+]i and [Ca2+]i and prevented both the veratridine-induced increases of [Na+]i and [Ca2+]i and the inhibition of lactate production. The data indicate a considerable Na+ influx via voltage-dependent Na+ channels during anoxia, which speeds up the decline in ATP and provokes an increase in [Ca2+]i. A massive Na+ and Ca2+ overload induced by veratridine failed to influence lactate synthesis directly, but initiated its inhibition.