Na(+)-K(+)-ATPase and Ca(2+) clearance proteins in smooth muscle: a functional unit.
The Na(+)-K(+)-ATPase (NKA) can affect intracellular Ca(2+) concentration regulation via coupling to the Na(+)-Ca(2+) exchanger and may be important in myogenic tone. We previously reported that in mice carrying a transgene for the NKA alpha(2)-isoform in smooth muscle (alpha(2sm+)), the alpha(2)-isoform protein as well as the alpha(1)-isoform (not contained in the transgene) increased to similar degrees (2-7-fold). Aortas from alpha(2sm+) mice relaxed faster from a KCl-induced contraction, hypothesized to be related to more rapid Ca(2+) clearance. To elucidate the mechanisms underlying this faster relaxation, we therefore measured the expression and distribution of proteins involved in Ca(2+) clearance. Na(+)-Ca(2+) exchanger, sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), and plasma membrane Ca(2+)-ATPase (PMCA) proteins were all elevated up to approximately fivefold, whereas actin, myosin light chain, and calponin proteins were not changed in smooth muscle from alpha(2sm+) mice. Interestingly, the corresponding Ca(2+) clearance mRNA levels were unchanged. Immunocytochemical data indicate that the Ca(2+) clearance proteins are distributed similarly in wild-type and alpha(2sm+) aorta cells. In studies measuring relaxation half-times from a KCl-induced contraction in the presence of pharmacological inhibitors of SERCA and PMCA, we estimated that together these proteins were responsible for approximately 60-70% of relaxation in aorta. Moreover, the percent contribution of SERCA and PMCA to relaxation rates in alpha(2sm+) aorta was not significantly different from that in wild-type aorta. The coordinate expressions of NKA and Ca(2+) clearance proteins without change in the relative contributions of each individual protein to smooth muscle function suggest that NKA may be but one component of a larger functional Ca(2+) clearance system.
Pritchard
Tracy J
TJ
Molecular and Cellular Physiology, Univ. of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0576, USA.
Bowman
Peggy Sue
PS
Jefferson
Andrew
A
Tosun
Metiner
M
Lynch
Ronald M
RM
Paul
Richard J
RJ
D000818:Animals; D001692:Biological Transport; D001794:Blood Pressure; D002118:Calcium / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology*; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014661:Vasoconstriction; D014664:Vasodilation
D027682:Cation Transport Proteins; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D019831:Sodium-Calcium Exchanger; D053499:Plasma Membrane Calcium-Transporting ATPases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C497344:Atp1a1 protein, mouse; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium