Elevation of the adenylate pool in rat cardiomyocytes by S-adenosyl-L-methionine

Rapid resynthesis of the adenylate pool in cardiac myocytes is important fo r recovery of contractility and normal function of regulatory mechanisms in the heart. Adenosine and adenine are thought to be the most effective subs trates for nucleotide synthesis, but the possibility of using other compoun ds has been studied very little in cardiomyocytes. In the present study, th e effect of S-adenosyl-L-methionine (SAM) on the adenylate pool of isolated cardiomyocytes was investigated and compared to the effect of adenine and adenosine. Adult rat cardiomyocytes were isolated using the collagenase per fusion technique. The cells were incubated in the presence of adenine deriv atives for 90 min followed by nucleotide determination by HPLC. The concent rations of adenine nucleotides expressed in nmol/mg of cell protein were in itially 22.1 +/- 1.4, 4.0 +/- 0.3 and 0.70 +/- 0.08 for ATP, ADP and AMP, r espectively (n = 10, +/-S.E.M.), and the total adenylate pool was 26.8 +/- 1.6, In the presence of 1.25 mM SAM in the medium, the adenylate pool incre ased by 5.2 +/- 0.4 nmol/mg of cell protein, but only if 1 mM ribose was ad ditionally present in the medium. No changes were observed with SAM alone. A similar increase (by 4.9 +/- 0.6 nmol/mg protein) was observed after incu bation with 1.25 mM adenine plus 1 mM ribose, but no increase was observed if ribose was omitted. Adenosine at 0.1 or 1.25 mM concentrations also caus ed an increase in the adenylate pool (by 5.2 +/- 1.0 and 5.2 +/- 0.9 nmol/m g protein, respectively), which in contrast to the SAM or adenine was indep endent of the additional presence of ribose. Thus, S-adenosyl-L-methionine could be used as a precursor of the adenylate pool in cardiomyocytes, which is as efficient in increasing the adenylate pool after 90 min of incubatio n as adenosine or adenine. Nucleotide synthesis from SAM involves the forma tion of adenine as an intermediate with its subsequent incorporation by ade nine phosphoribosyltransferase.