Spermidine decreases Na+,K+-ATPase activity through NMDA receptor and protein kinase G activation in the hippocampus of rats

Fabiano B. Carvalho, Carlos F. Mello, Patricia C. Marisco, Raquel Tonello, Bruna A. Girardi, Juliano Ferreira, Mauro S. Oliveira, Maribel A. Rubin

Index: Eur. J. Pharmacol. 684(1-3) , 79-86, (2012)

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Abstract

Spermidine is an endogenous polyamine with a polycationic structure present in the central nervous system of mammals. Spermidine regulates biological processes, such as Ca2+ influx by glutamatergic N-methyl-d-aspartate receptor (NMDA receptor), which has been associated with nitric oxide synthase (NOS) and cGMP/PKG pathway activation and a decrease of Na+,K+-ATPase activity in rats' cerebral cortex synaptosomes. Na+,K+-ATPase establishes Na+ and K+ gradients across membranes of excitable cells and by this means maintains membrane potential and controls intracellular pH and volume. However, it has not been defined whether spermidine modulates Na+,K+-ATPase activity in the hippocampus. In this study we investigated whether spermidine alters Na+,K+-ATPase activity in slices of hippocampus from rats, and possible underlying mechanisms. Hippocampal slices and homogenates were incubated with spermidine (0.05–10μM) for 30min. Spermidine (0.5 and 1μM) decreased Na+,K+-ATPase activity in slices, but not in homogenates. MK-801 (100 and 10μM), a non-competitive antagonist of NMDA receptor, arcaine (0.5μM), an antagonist of the polyamine binding site at the NMDA receptor, and L-NAME (100μM), a NOS inhibitor, prevented the inhibitory effect of spermidine (0.5μM). ODQ (10μM), a guanylate cyclase inhibitor, and KT5823 (2μM), a protein kinase G inhibitor, also prevented the inhibitory effect of spermidine on Na+,K+-ATPase activity. Spermidine (0.5 and 1.0μM) increased NO2 plus NO3 (NOx) levels in slices, and MK-801 (100μM) and arcaine (0.5μM) prevented the effect of spermidine (0.5μM) on the NOx content. These results suggest that spermidine-induced decrease of Na+,K+-ATPase activity involves NMDA receptor/NOS/cGMP/PKG pathway.