Am J Physiol Cell Physiol AJP: Cell Physiology
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Am J Physiol Cell Physiol 259: C987-C994, 1990;
0363-6143/90 $5.00
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AJP - Cell Physiology, Vol 259, Issue 6 C987-C994, Copyright © 1990 by American Physiological Society

ARTICLES

Synthesis, transfer, and phosphorylation of phosphoinositides in cardiac membranes

R. A. Wolf
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.

Compartmentation of phosphoinositide synthesis and transfer of endogenous phosphatidylinositol (PI) were characterized in membrane fractions prepared from rabbit myocardium. De novo synthesis of PI was highly enriched in free sarcoplasmic reticulum (551 pmol.mg-1. min-1) compared with that in sarcolemma (26.8 pmol.mg-1. min-1) and junctional sarcoplasmic reticulum (178 pmol.mg-1. min-1). In contrast, PI phosphorylation was highly enriched in sarcolemma (2.69 nmol.mg-1.min-1) compared with that in free sarcoplasmic reticulum (0.22 nmol.mg-1.min-1) and junctional sarcoplasmic reticulum (0.38 nmol.mg-1.min-1). Phosphorylation of endogenous phosphatidylinositol 4-phosphate to phosphatidylinositol 4,5-bisphosphate was also enriched in sarcolemma (38.5 pmol.mg-1.min-1) compared with that in free sarcoplasmic reticulum (less than 5.0 pmol.mg-1.min-1) and junctional sarcoplasmic reticulum (6.5 pmol.mg-1.min-1). Transfer of endogenous PI was characterized as a mechanism to overcome compartmentation of PI synthesis in cardiac membranes. A 29-kDa PI transfer protein was purified 1,500-fold from cytosol of rabbit myocardium. Both cytosol and purified PI transfer protein catalyzed the transfer of endogenous PI from microsomal sites of synthesis to sarcolemma. In conclusion, synthesis of PI is highly enriched in free sarcoplasmic reticulum, whereas phosphorylation of phosphoinositides is highly enriched in sarcolemma. A 29-kDa PI transfer protein in myocardial cytosol can mediate in vitro transfer of de novo-synthesized PI to the sarcolemma.


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C. Nasuhoglu, S. Feng, Y. Mao, I. Shammat, M. Yamamato, S. Earnest, M. Lemmon, and D. W. Hilgemann
Modulation of cardiac PIP2 by cardioactive hormones and other physiologically relevant interventions
Am J Physiol Cell Physiol, July 1, 2002; 283(1): C223 - C234.
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