TY - JOUR
T1 - Phospholemman-phosphorylation mediates the β-adrenergic effects on Na/K pump function in cardiac myocytes
AU - Despa, Sanda
AU - Bossuyt, Julie
AU - Han, Fei
AU - Ginsburg, Kenneth S.
AU - Jia, Li Guo
AU - Kutchai, Howard
AU - Tucker, Amy L.
AU - Bers, Donald M.
PY - 2005/8/5
Y1 - 2005/8/5
N2 - Cardiac sympathetic stimulation activates β-adrenergic (β-AR) receptors and protein kinase A (PKA) phosphorylation of proteins involved in myocyte Ca regulation. The Na/K-ATPase (NKA) is essential in regulating intracellular [Na] ([Na]i), which in turn affects [Ca]i via Na/Ca exchange. However, how PKA modifies NKA function is unknown. Phospholemman (PLM), a member of the FXYD family of proteins that interact with NKA in various tissues, is a major PKA substrate in heart. Here we tested the hypothesis that PLM phosphorylation is responsible for the PKA effects on cardiac NKA function using wild-type (WT) and PLM knockout (PLM-KO) mice. We measured NKA-mediated [Na]i decline and current (IPump) to assess β-AR effects on NKA function in isolated myocytes. In WT myocytes, 1 μmol/L isoproterenol (ISO) increased PLM phosphorylation and stimulated NKA activity mainly by increasing its affinity for internal Na (Km decreased from 18.8± 1.4 to 13.6 ± 1.5 mmol/L), with no significant effect on the maximum pump rate. This led to a significant decrease in resting [Na]i (from 12.5 ± 1.8 to 10.5 ± 1.4 mmol/L). In PLM-KO mice under control conditions Km (14.2 ± 1.5 mmol/L) was lower than in WT, but comparable to that for WT in the presence of ISO. Furthermore, ISO had no significant effect on NKA function in PLM-KO mice. ATPase activity in sarcolemmal vesicles also showed a lower K m(Na) in PLM-KO versus WT (12.9 ± 0.9 versus 16.2 ± 1.5). Thus, PLM inhibits NKA activity by decreasing its [Na]i affinity, and this inhibitory effect is relieved by PKA activation. We conclude that PLM modulates the NKA function in a manner similar to the way phospholamban affects the related SR Ca-ATPase (inhibition of transport substrate affinity, that is relieved by phosphorylation).
AB - Cardiac sympathetic stimulation activates β-adrenergic (β-AR) receptors and protein kinase A (PKA) phosphorylation of proteins involved in myocyte Ca regulation. The Na/K-ATPase (NKA) is essential in regulating intracellular [Na] ([Na]i), which in turn affects [Ca]i via Na/Ca exchange. However, how PKA modifies NKA function is unknown. Phospholemman (PLM), a member of the FXYD family of proteins that interact with NKA in various tissues, is a major PKA substrate in heart. Here we tested the hypothesis that PLM phosphorylation is responsible for the PKA effects on cardiac NKA function using wild-type (WT) and PLM knockout (PLM-KO) mice. We measured NKA-mediated [Na]i decline and current (IPump) to assess β-AR effects on NKA function in isolated myocytes. In WT myocytes, 1 μmol/L isoproterenol (ISO) increased PLM phosphorylation and stimulated NKA activity mainly by increasing its affinity for internal Na (Km decreased from 18.8± 1.4 to 13.6 ± 1.5 mmol/L), with no significant effect on the maximum pump rate. This led to a significant decrease in resting [Na]i (from 12.5 ± 1.8 to 10.5 ± 1.4 mmol/L). In PLM-KO mice under control conditions Km (14.2 ± 1.5 mmol/L) was lower than in WT, but comparable to that for WT in the presence of ISO. Furthermore, ISO had no significant effect on NKA function in PLM-KO mice. ATPase activity in sarcolemmal vesicles also showed a lower K m(Na) in PLM-KO versus WT (12.9 ± 0.9 versus 16.2 ± 1.5). Thus, PLM inhibits NKA activity by decreasing its [Na]i affinity, and this inhibitory effect is relieved by PKA activation. We conclude that PLM modulates the NKA function in a manner similar to the way phospholamban affects the related SR Ca-ATPase (inhibition of transport substrate affinity, that is relieved by phosphorylation).
KW - Ion channels
KW - Na pump
KW - Phospholemman
KW - Signal transduction
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U2 - 10.1161/01.RES.0000176532.97731.e5
DO - 10.1161/01.RES.0000176532.97731.e5
M3 - Article
C2 - 16002746
AN - SCOPUS:23344445947
SN - 0009-7330
VL - 97
SP - 252
EP - 259
JO - Circulation Research
JF - Circulation Research
IS - 3
ER -