Effect of cardiazol on sodium-potassium-activated adenosine triphosphatase of the rat brain in vivo

SHORT COMMUNICATIONS

413

Effect of cardiazol on sodium.potassium-activated adenosine triphosphatase of the rat brain in vivo In the course of an investigation on the effects ofintracranial injection ofouabain in the rat and the guinea-pig ~-3, a marked decrease of sodium-potassium-activated adenosine triphosphatasc activky was found in the i~ected brain 7. In view of the frequent occurrence of seizures in animals treated with ouabain, convulsions were induced in rats with cardiazol (pentylenetetrazol), and the Na +, K + ATPase activity was subsequently estimated. This experiment showed that the activity of this enzyme is actually increased. Cardiazol (pentylenetetrazol) was injected intraperitoneally in 20 adult SpragueDawley rats at a convulsant dose (50 mg per kg). At the end of the convulsions the animals promptly recovered. The rats were decapitated at different time intervals after the injection (5-15 rain, 2 h, 7 days). The cerebral cortex was dissected and homogenated in distilled water. The homogenate was lyophilized at - - 2 0 ° and stored at ~ 1 1 °. The activity of total ATPase, Mg 2+ and Na +, K + ATPase was assayed according to Bonting et al. 4. Three ml of substrate media containing 0.5 mg of dried homogenate were incubated with ATP*. Two samples of homogenate were assayed in most animals. Twelve adult Sprague-Dawley rats were used as controls.

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Fig. 1. ATPase activity of the rat cerebral cortex after intraperitoneal injection of cardiazol (50 mg per kg). Activities expressed in m M ATP split/h/g dry wt of whole tissue at 37 °. Heavy black line and triangles: Mg2 + ATPase (MgA). Heavy black and white line and open circles: N a +, K + ATPase (NaKA). Black circles: Total A T P a s e / T A ) . Light continuous and broken lines: A T P ~ e activity in controls. Dotting represents the standard error ( p = 95 %). * Adenosine 5'.triphosphate, disodium salt (SIGMA, Chemical Co., St. Louis, Mo.).

Brain Research, 1 (1966) 413-414

414

SHORT COMMUNICATIONS

The N a +, K + activity in the brain was already increased 5 min after the injection of cardiazol. In the first 15 rain the increase varied from animal to animal; after 2 h it became constant ( + 2 0 % ) and was still at the same level 2 days after the injection. Seven days after the injection the Na +, K + activity of the brain had returned to r, ormal (Fig. 1). Total ATPase activity (Mg 2+ and N a +, K + ATPase) was not increased: in brains showing increased N a +, K + activity the Mg 2+ ATPase activity was proportionately decreased. A marked drop in the electrical conductivity of the cerebral cortex has been observed during cardiazol-induced seizures in the rabbit 5. This drop in conductivity was interpreted as indicating a transport of electrolytes into neuronal elements. An increase in the membrane potential of neurones has been observed in snails following intracellular injection of sodium ions °. This hyperpolarization was inhibited by ouabain and was considered to be the result of a stimulation of an electrogenic sodium p u m p in the nerve cell. In view of these findings our results may indicate that a passage of sodium into cellular elements during cardiazol-induced convulsions enhances the N a +, K + activity of the cerebral cortex. This enzyme is now considered to be responsible for the active transport of ions across the cell membrane s . The mechanism whereby certain compounds enhance the activities of microsomal enzymes is not known. An interesting finding in our experiment was the decrease in the activity of M g 2+ ATPase, which parallels the increase in N a ÷, K + activity. It is not known whether activity with Mg 2+ alone is due to a different enzyme, or whether it is a part of the same enzyme system s. Istituto di Anatomia Comparata "G. B. Grassr, Universitd di Roma Roma (Italy)

AMICO BIGNAMI GUIDO PALLADINI GIORGIO "'IENTURINI

| BIGNAMI, A., AND PALLADINI, G., Ricerche sull'inibizione in vivo dell'ATPasi di membrana. Riproduzione sperimentale dello stato spongioso cerebrale e di scariche elettroencefalografiche pseudoritmiche continue, Rend. Ace. naz. Lincei, VIII, 38 (1965) 253-258. 2 BIGNA.'m,A., ANDPALLADrN,,G., Experimental~y produced cerebral status spongiosus and continuous pseudorhythmic electroencephalographic discharges with a membrane ATPase inhibitor in the rat, Nature, 209 (1966) 413-414. 3 BIGNAMI,A., AND PALLADIm,G., Subacute spongiform encephalopathy. An experimental study. Proc. 5th Int. Congr. Neuropath., Ziirich, 1965, in press. 4 BONTING, S. L., SIMON,K. A., AND HAWKINS, N. M., Studies on sodium-potassium-activated adenosine triphosphatase, Arch. Biochem. Biophys., 95 (1961) 416-423. 5 HARREVELDVAN,A., ANDSCHAD[,J. P., Changes in the electrical conductivity of cerebral cortex during seizure activity, Exp. Neurol., 5 (1962) 383-399. 6 KERKtrr, G. A., AND THOMAS,R. C., An electrogenic sodium pump in snail nerve-cells, Comp. Biochem. Physiol., 14 (1965) 167-183. 7 PALLADINI,G., BIGNAMI,A., AND VENTURINI, G., Prime osservazioni biochimiche sull'inibizione dell'ATPasi di membrana nel ratto in vivo, Rend. Acc. Naz. Lincei, VIII, 39 (1965) 372-374. 8 SKOU,J. C., Enzymatic basis for active transport of Na + and K + across cell membrane, Physiol. Rev., 45 (1965) 596-617. (Received March 1l th, 1966) Brain Research, 1 (1966)413-414