May 1, 1997
View Full PaperInhibition of Myocardial Crossbridge Cycling by Hypoxic Endothelial Cells
Key Result
Hypoxic endothelial cells released an unidentified substance that induced rapid, potent, and reversible inhibition of isolated cardiac myocyte contraction and depressed cardiac myosin ATPase activity.
Structured PICO
Does acute moderate hypoxia induce endothelial cells to release factors that inhibit myocardial crossbridge cycling?
P
Population
Cultured endothelial cells from several vascular beds, isolated cardiac myocytes, human skinned soleus muscle fibers, and cardiac/smooth muscle myosin
E
Exposure
Superfusion with hypoxic physiological buffer solution (PO2, 40 to 50 mm Hg)
C
Comparator
Superfusion with normoxic physiological buffer solution (equilibrated with room air; PO2, approximately 160 mm Hg)
O
Outcome
Effect of endothelial cell superfusates on isolated cardiac myocyte contraction, cytosolic Ca2+ transients, unloaded shortening velocity, actin motility, and myosin ATPase activitysurrogate
Cultured endothelial cells respond to acute moderate hypoxia by releasing an unidentified substance that inhibits myocardial crossbridge cycling independent of Ca2+ signaling, suggesting a mechanism for regulating oxygen supply-demand balance in conditions like myocardial hibernation.
Abstract
Previous studies have shown that cardiac endothelial cells release substances that influence myocardial contraction. Since PO2 is an important stimulus that modulates endothelial function, we investigated the effects of acute moderate hypoxia and reoxygenation on the release of cardioactive factors by endothelial cells. Endothelial cells cultured from several vascular beds were superfused with normoxic (equilibrated with room air; PO2, approximately 160 mm Hg) or hypoxic (PO2, 40 to 50 mm Hg) physiological buffer solution, and the superfusates were reequilibrated to a PO2 of approximately 160 mm Hg and then tested for their effects on various myocardial assays. Endothelial cell viability and buffer ionic composition were unaltered after the superfusion procedures. The superfusates of hypoxic endothelial cells induced rapid, potent, reversible inhibition of isolated cardiac myocyte contraction without reducing cytosolic Ca2+ transients. This activity was not lost after heating (95 degrees C) and was present in low molecular weight (Mr, <500) superfusate fractions. Hypoxic endothelial superfusate reduced unloaded shortening velocity of human skinned soleus muscle fibers. It markedly depressed in vitro actin motility over cardiac myosin and reduced the rate of actin-activated cardiac myosin ATPase activity but had no effect on corresponding smooth muscle myosin assays. Reoxygenation of hypoxic endothelial cells resulted in loss of this inhibitory activity. These data indicate that cultured endothelial cells respond to acute moderate hypoxia by releasing an unidentified substance(s) that inhibits myocardial crossbridge cycling, independent of Ca2+ or other second messenger signaling pathways. Such a mechanism could have important implications for the regulation of oxygen supply-demand balance in the heart and be relevant to conditions such as myocardial hibernation.