Characterization of electrogenic Na/K pump in rat neostriatal neurons |
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Authors: | Mitsutoshi Munakata Mika Fujimoto Young-Ho Jin Norio Akaike |
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Institution: | a Department of Pediatrics, Tohoku University School of Medicine, Sendai 980-77, Japan b Department of Neurology and Physiology, Faculty of Medicine, Kyushu University, Fukuoka 812-82, Japan |
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Abstract: | The electrogenic Na/K pump current (Ip) was studied in the dissociated neostriatal neurons of the rat by using the nystatin-perforated patch recording mode. The Ip was activated by external K+ in a concentration-dependent manner with an EC50 of 0.7 mM at a holding potential (VH) of ?40 mV. Other monovalent cations also caused Ip and the order of potency was Tl+>K+, Rb+>NH4+, Cs+>>>Li+. The Ip decreased with membrane hyperpolarization in an external solution containing 150 mM Na+, while the Ip did not show such voltage dependency without external Na+. Ouabain showed a steady-state inhibition of Ip in a concentration- and temperature-dependent manner at a VH of ?40 mV. The IC50 values at 20 and 30°C were 7.1×10?6 and 1.3×10?6 M, respectively. The decay of Ip after adding ouabain well fitted with a single exponential function. At a VH of ?40 Mv, the association (k+1) and dissociation (k?1) rate constants estimated from the time constant of the current decay at 20°C were 4.0×102 s?1 M?1 and 6.3×10?3 s?1, respectively. At 30°C, k+1 increased to 2.8×103 s?1 M?1 while k?1 showed no such change with a value of 1.8×10?3 s?1. A continuous Na+ influx was demonstrated by both the Na+-dependent leakage current and tetrodotoxin-sensitive Na+ current, which resulted in the continuous activation of the Na/K pump. It was thus concluded that the Na/K pump activity was well-maintained in the dissociated rat neostriatal neurons with distinct functional properties and that the activity of the pump was tightly connected with Na+ influxes. |
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Keywords: | Na/K pump Voltage dependency Neostriatal neuron |
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