Poly(adenosine diphosphate ribose) metabolism and regulation of myocardial cell growth by oxygen

Abstract

Control of the rate of cardiac cell division by oxygen occurs most probably by altering the redox state of a control substance, e.g. NAD+⇌NADH. NAD+(and not NADH) forms poly(ADP-ribose), an inhibitor of DNA synthesis, in a reaction catalysed by poly(ADP-ribose) polymerase. Lower partial pressure of oxygen, which increases the rate of division, would shift NAD+→NADH, decrease poly(ADP-ribose) synthesis, and increase DNA synthesis. Chick-embryo heart cells grown in culture in 20% O2 (in which they divide more slowly than in 5% O2) did exhibit greater poly(ADP-ribose) polymerase activity (+83%, P<0.001) than when grown in 5% O2. Reaction product was identified as poly(ADP-ribose) by its insensitivity to deoxyribonuclease, ribonuclease, NAD glycohydrolase, Pronase, trypsin and micrococcal nuclease, and by its complete digestion with snake-venom phosphodiesterase to phosphoribosyl-AMP and AMP. Isolation of these digestion products by Dowex 1 (formate form) column chromatography and paper chromatography allowed calculation of average poly(ADP-ribose) chain length, which was 15–26% greater in 20% than in 5% O2. Thus in 20% O2 the increase in poly(ADP-ribose) formation results from chain elongation. Formation of new chains also occurs, probably to an even greater degree than chain elongation. Additionally, poly(ADP-ribose) polymerase has very different Km and Vmax. values and pH optima in 20% and 5% O2. These data suggest that poly(ADP-ribose) metabolism participates in the regulation of heart-cell division by O2, probably by several different mechanisms.