%0 Journal Article %1 Desp_2007_321 %A Despa, Sanda %A Bers, Donald M %D 2007 %J Am. J. Physiol. Cell Physiol. %K /&/ ATPase, Animals; Cardiac, Dose-Response Drug; Enzyme Factors Formamides, Heart Inhibitors, Isoenzymes, Membrane Myocytes, Ouabain, Potentials; Rats; Relationship, Sarcolemma, Sodium, Sodium-Potassium-Exchanging Time Ventricles, antagonists cytology/enzymology; drug effects/enzymology; inhibitors/metabolism; metabolism; pharmacology; %N 1 %P C321--C327 %R 10.1152/ajpcell.00597.2006 %T Functional analysis of Na$^+$/K$^+$-ATPase isoform distribution in rat ventricular myocytes. %U http://dx.doi.org/10.1152/ajpcell.00597.2006 %V 293 %X The Na$^+$/K$^+$-ATPase (NKA) is the main route for Na$^+$ extrusion from cardiac myocytes. Different NKA alpha-subunit isoforms are present in the heart. NKA-alpha1 is predominant, although there is a variable amount of NKA-alpha2 in adult ventricular myocytes of most species. It has been proposed that NKA-alpha2 is localized mainly in T-tubules (TT), where it could regulate local Na$^+$/Ca$^2+$ exchange and thus cardiac myocyte Ca$^2+$. However, there is controversy as to where NKA-alpha1 vs. NKA-alpha2 are localized in ventricular myocytes. Here, we assess the TT vs. external sarcolemma (ESL) distribution functionally using formamide-induced detubulation of rat ventricular myocytes, NKA current (I(Pump)) measurements and the different ouabain sensitivity of NKA-alpha1 (low) and NKA-alpha2 (high) in rat heart. Ouabain-dependent I(Pump) inhibition in control myocytes indicates a high-affinity NKA isoform (NKA-alpha2, K(1/2) = 0.38 +/- 0.16 microM) that accounts for 29.5 +/- 1.3\% of I(Pump) and a low-affinity isoform (NKA-alpha1, K(1/2) = 141 +/- 17 microM) that accounts for 70.5\% of I(Pump). Detubulation decreased cell capacitance from 164 +/- 6 to 120 +/- 8 pF and reduced I(Pump) density from 1.24 +/- 0.05 to 1.02 +/- 0.05 pA/pF, indicating that the functional density of NKA is significantly higher in TT vs. ESL. In detubulated myocytes, NKA-alpha2 accounted for only 18.2 +/- 1.1\% of I(Pump). Thus, approximately 63\% of I(Pump) generated by NKA-alpha2 is from the TT (although TT are only 27\% of the total sarcolemma), and the NKA-alpha2/NKA-alpha1 ratio in TT is significantly higher than in the ESL. The functional density of NKA-alpha2 is approximately 4.5 times higher in the T-tubules vs. ESL, whereas NKA-alpha1 is almost uniformly distributed between the TT and ESL.

@article{Desp_2007_321, abstract = {The {N}a$^{+}$/{K}$^{+}$-ATPase (NKA) is the main route for {N}a$^{+}$ extrusion from cardiac myocytes. Different NKA alpha-subunit isoforms are present in the heart. NKA-alpha1 is predominant, although there is a variable amount of NKA-alpha2 in adult ventricular myocytes of most species. It has been proposed that NKA-alpha2 is localized mainly in T-tubules (TT), where it could regulate local {N}a$^{+}$/{C}a$^{2+}$ exchange and thus cardiac myocyte {C}a$^{2+}$. However, there is controversy as to where NKA-alpha1 vs. NKA-alpha2 are localized in ventricular myocytes. Here, we assess the TT vs. external sarcolemma (ESL) distribution functionally using formamide-induced detubulation of rat ventricular myocytes, NKA current (I(Pump)) measurements and the different ouabain sensitivity of NKA-alpha1 (low) and NKA-alpha2 (high) in rat heart. Ouabain-dependent I(Pump) inhibition in control myocytes indicates a high-affinity NKA isoform (NKA-alpha2, K(1/2) = 0.38 +/- 0.16 microM) that accounts for 29.5 +/- 1.3\% of I(Pump) and a low-affinity isoform (NKA-alpha1, K(1/2) = 141 +/- 17 microM) that accounts for 70.5\% of I(Pump). Detubulation decreased cell capacitance from 164 +/- 6 to 120 +/- 8 pF and reduced I(Pump) density from 1.24 +/- 0.05 to 1.02 +/- 0.05 pA/pF, indicating that the functional density of NKA is significantly higher in TT vs. ESL. In detubulated myocytes, NKA-alpha2 accounted for only 18.2 +/- 1.1\% of I(Pump). Thus, approximately 63\% of I(Pump) generated by NKA-alpha2 is from the TT (although TT are only 27\% of the total sarcolemma), and the NKA-alpha2/NKA-alpha1 ratio in TT is significantly higher than in the ESL. The functional density of NKA-alpha2 is approximately 4.5 times higher in the T-tubules vs. ESL, whereas NKA-alpha1 is almost uniformly distributed between the TT and ESL.}, added-at = {2009-06-03T11:20:58.000+0200}, author = {Despa, Sanda and Bers, Donald M}, biburl = {https://www.bibsonomy.org/bibtex/2ab05764408065e802391d90fadc786f3/hake}, description = {The whole bibliography file I use.}, doi = {10.1152/ajpcell.00597.2006}, file = {Desp_2007_321.pdf:Desp_2007_321.pdf:PDF}, institution = {Dept. of Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave., Maywood, IL 60153, USA.}, interhash = {772b8f649bd1b5d3d59f29e21632a9d8}, intrahash = {ab05764408065e802391d90fadc786f3}, journal = {Am. J. Physiol. Cell Physiol.}, keywords = {/&/ ATPase, Animals; Cardiac, Dose-Response Drug; Enzyme Factors Formamides, Heart Inhibitors, Isoenzymes, Membrane Myocytes, Ouabain, Potentials; Rats; Relationship, Sarcolemma, Sodium, Sodium-Potassium-Exchanging Time Ventricles, antagonists cytology/enzymology; drug effects/enzymology; inhibitors/metabolism; metabolism; pharmacology;}, month = Jul, number = 1, pages = {C321--C327}, pdf = {Desp_2007_321.pdf}, pii = {00597.2006}, pmid = {17392375}, timestamp = {2009-06-03T11:21:09.000+0200}, title = {Functional analysis of {N}a$^{+}$/{K}$^{+}$-ATPase isoform distribution in rat ventricular myocytes.}, url = {http://dx.doi.org/10.1152/ajpcell.00597.2006}, volume = 293, year = 2007 }