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Nucleotides가 세포막 투과도에 미치는 영향

Effects of Various Nucleotides on the Membrane Permeability

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The present study was designed to investigate i) the action of various nucleotides on membrane permeability of rat red blood cell and hepatocyte for Na<sup>+</sup> and Rb<sup>+</sup> ii) the characteristics of purinoceptors on these cell membranes. Blood from Sprague-Dawley rats was obtained by carotid arterial cannulation. Red blood cells were then washed 3 times with saline at 4˚C. Hepatic parenchymal cells were isolated from rat livers by using a modification of the Berry and Friend (1969) method. For the Na<sup>+</sup> influx studies, isolated RBC and hepatocyte were incubated in incubation medium containing <sup>22</sup>Na<sup>+</sup>0.2 μCi/ml at 37℃. After various time intervals samples were removed from the incubation flask and washed out 3 times with ice-cold washing solutions. Cells were destroyed by adding Triton X-100 and TCA solution. After centrifugation, the supernatants were assayed for <sup>22</sup>Na<sup>+</sup> by gamma counter. <sup>86</sup>Rb<sup>+</sup> was used to simulate K<sup>+</sup> in these K<sup>+</sup>efflux studies. Isolated hepatocytes were incubated for 60 min in the loading solution containing <sup>86</sup>Rb<sup>+</sup> 10 μCi/ml at 37℃. After loading, the cells washed out 3 times by centrifugation with washing solution. The cells were incubated in buffer solution at 37℃. At intervals thereafter, samples were removed and centrifuged. The supernatants were analyzed for <sup>86</sup>Rb<sup>+</sup> by liquid scintillation counter. The main results of the experiments were: 1) ATP and ATPP increased in both <sup>22</sup>Na<sup>+</sup> influx and <sup>86</sup>Rb<sup>+</sup> efflux in the red blood cell. Although ADP showed a tendency to increase in RBC membrane permeability for <sup>22</sup>Na<sup>+</sup> and <sup>86</sup>Rb<sup>+</sup>, the changes were not significantly different from the control. 2) The Significant changes in <sup>22</sup>Na<sup>+</sup> and <sup>86</sup>Rb<sup>+</sup> flux by ATP were also demonstrated in hepatocyte. ATPP and ADP showed a tendency to increase in hepatocyte membrane permeability for both ions. 3) Other nucleoside triphosphates-ITP, GTP and CTP-did not change in membrane permeability for <sup>22</sup>Na<sup>+</sup> and <sup>86</sup>Rb<sup>+</sup> in RBC and hepatocyte. In conclusion, not only ATP but also ATPP activate purinoceptors and change in membrane permeability for Na<sup>+</sup> and K<sup>+</sup>. In order to activate purinoceptors on the cell membrane, the nucleotides have to possess intact adenine moiety and three phosphates or more in its molecule.

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