%0 Journal Article %1 Desp_2003_4157 %A Despa, Sanda %A Bers, Donald M %D 2003 %J Biophys. J. %K 12770918 ATPase, Adaptation, Animals, Biological, Calcium, Capacitance, Cardiac, Cell Cells, Comparative Computer Cultured, Diffusion, Distribution, Electric Gov't, H.S., Heart Intracellular Membrane Models, Muscle Myocytes, Non-U.S. P., P.H.S., Physiological, Potentials, Rabbits, Rats, Research Sarcolemma, Simulation, Size, Sodium, Space, Study, Support, Tissue U.S. Ventricles, {N}a$^{+}$-{K}$^{+}$-Exchanging %N 6 %P 4157--4166 %T Na/K pump current and Na(i) in rabbit ventricular myocytes: local Na(i) depletion and Na buffering. %U http://www.biophysj.org/cgi/content/full/84/6/4157 %V 84 %X Na/K pump current (I(pump)) and intracellular Na concentration (Na(i)) were measured simultaneously in voltage-clamped rabbit ventricular myocytes, under conditions where Na(i) is controlled mainly by membrane transport. Upon abrupt pump reactivation (after 10-12 min blockade), I(pump) decays in two phases. Initially, I(pump) declines with little Na(i) change, whereas the second phase is accompanied by Na(i) decline. Initial I(pump) sag was still present at external K = 15 mM, but prevented by Na(i) approximately 100 mM. Initial I(pump) sag might be explained by subsarcolemmal Na(i) (Na(SL)) depletion produced by rapid Na extrusion and I(pump). Brief episodes of pump blockade allowed Na(SL) repletion, since peak postblockade I(pump) exceeded I(pump) at the end of previous activation (without appreciably altered global Na(i)). The apparent K(m) for Na(i) was higher for continuous I(pump) activation than peak I(pump) (14.1 +/- 0.2 vs. 11.2 +/- 0.2 mM), whereas that based on dNa(i)/dt matched peak I(pump) (11.6 +/- 0.3 mM). Na(SL) depletion (vs. Na(i)) could be as high as 3 mM for Na(i) approximately 18-20 mM. A simple diffusion model indicates that such Na(SL) depletion requires a Na diffusion coefficient 10(3)- to 10(4)-fold below that expected in bulk cytoplasm (although this could be subsarcolemmal only). I(pump) integrals and Na(i) decline were used to estimate intracellular Na buffering, which is slight (1.39 +/- 0.09).

@article{Desp_2003_4157, abstract = {Na/K pump current (I(pump)) and intracellular Na concentration ([Na](i)) were measured simultaneously in voltage-clamped rabbit ventricular myocytes, under conditions where [Na](i) is controlled mainly by membrane transport. Upon abrupt pump reactivation (after 10-12 min blockade), I(pump) decays in two phases. Initially, I(pump) declines with little [Na](i) change, whereas the second phase is accompanied by [Na](i) decline. Initial I(pump) sag was still present at external [K] = 15 mM, but prevented by [Na](i) approximately 100 mM. Initial I(pump) sag might be explained by subsarcolemmal [Na](i) ([Na]({SL})) depletion produced by rapid Na extrusion and I(pump). Brief episodes of pump blockade allowed [Na]({SL}) repletion, since peak postblockade I(pump) exceeded I(pump) at the end of previous activation (without appreciably altered global [Na](i)). The apparent K(m) for [Na](i) was higher for continuous I(pump) activation than peak I(pump) (14.1 +/- 0.2 vs. 11.2 +/- 0.2 mM), whereas that based on d[Na](i)/dt matched peak I(pump) (11.6 +/- 0.3 mM). [Na]({SL}) depletion (vs. [Na](i)) could be as high as 3 mM for [Na](i) approximately 18-20 mM. A simple diffusion model indicates that such [Na]({SL}) depletion requires a Na diffusion coefficient 10(3)- to 10(4)-fold below that expected in bulk cytoplasm (although this could be subsarcolemmal only). I(pump) integrals and [Na](i) decline were used to estimate intracellular Na buffering, which is slight (1.39 +/- 0.09).}, added-at = {2009-06-03T11:20:58.000+0200}, author = {Despa, Sanda and Bers, Donald M}, biburl = {https://www.bibsonomy.org/bibtex/2dc029921d4f2214b96ef12a0d8acc8bb/hake}, description = {The whole bibliography file I use.}, file = {Desp_2003_4157.pdf:Desp_2003_4157.pdf:PDF}, interhash = {9ce127ab4d882f2f38718d044cbb39b7}, intrahash = {dc029921d4f2214b96ef12a0d8acc8bb}, journal = {Biophys. J.}, key = 67, keywords = {12770918 ATPase, Adaptation, Animals, Biological, Calcium, Capacitance, Cardiac, Cell Cells, Comparative Computer Cultured, Diffusion, Distribution, Electric Gov't, H.S., Heart Intracellular Membrane Models, Muscle Myocytes, Non-U.S. P., P.H.S., Physiological, Potentials, Rabbits, Rats, Research Sarcolemma, Simulation, Size, Sodium, Space, Study, Support, Tissue U.S. Ventricles, {N}a$^{+}$-{K}$^{+}$-Exchanging}, month = Jun, number = 6, pages = {4157--4166}, pmid = {12770918}, timestamp = {2009-06-03T11:21:09.000+0200}, title = {Na/K pump current and [Na](i) in rabbit ventricular myocytes: local [Na](i) depletion and Na buffering.}, url = {http://www.biophysj.org/cgi/content/full/84/6/4157}, volume = 84, year = 2003 }