Cyclic GMP-dependent protein kinase stimulates the plasmalemmal Ca2+ pump of smooth muscle via phosphorylation of phosphatidylinositol.
The effect of phosphorylation by cyclic GMP-dependent protein kinase (G-kinase) on the activity of the plasmalemmal Ca2+-transport ATPase was studied on isolated plasma membranes and on the ATPase purified from pig erythrocytes and from the smooth muscle of pig stomach and pig aorta. Incubation with G-kinase resulted, in both smooth-muscle preparations, but not in the erythrocyte ATPase, in a higher Ca2+ affinity and in an increase in the maximal rate of Ca2+ uptake. Cyclic AMP-dependent protein kinase (A-kinase) did not exert such an effect. The stimulation of the (Ca2+ + Mg2+)-dependent ATPase activity of the purified Ca2+ pump reconstituted in liposomes depended on the phospholipid used for reconstitution. The stimulation of the (Ca2+ + Mg2+)-ATPase activity by G-kinase was only observed in the presence of phosphatidylinositol (PI). G-kinase, but not A-kinase, stimulated the phosphorylation of PI to phosphatidylinositol phosphate (PIP) in a preparation of (Ca2+ + Mg2+)-ATPase obtained by calmodulin affinity chromatography from smooth muscle, but not in a similar preparation from erythrocytes. Adenosine inhibited both the phosphorylation of PI and the stimulation of the (Ca2+ + Mg2+)-ATPase by G-kinase. In the absence of G-kinase the (Ca2+ + Mg2+)-ATPase was stimulated by the addition of PIP, but not by PI. In contrast with previous results of Furukawa & Nakamura [(1987) J. Biochem (Tokyo) 101, 287-290], no convincing evidence for a phosphorylation of the (Ca2+ + Mg2+)-ATPase was found. Evidence is presented showing that the apparent phosphorylation occurs in a contaminant protein, possibly myosin light-chain kinase. It is proposed that G-kinase stimulates the plasmalemmal Ca2+ pump of smooth-muscle cells indirectly via the phosphorylation of an associated PI kinase.
Vrolix
M
M
Laboratory of Physiology, Katholieke Universiteit Leuven, Belgium.
Raeymaekers
L
L
Wuytack
F
F
Hofmann
F
F
Casteels
R
R
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000493:pharmacokinetics*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D006152:Cyclic GMP / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects / Q000201:enzymology; D015151:Immunoblotting; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism* / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000494:pharmacology*; D013268:Stimulation, Chemical; D013552:Swine
D010716:Phosphatidylinositols; D010750:Phosphoproteins; D011494:Protein Kinases; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D006152:Cyclic GMP; D002118:Calcium