Nature of Endogenous Substrates Used to Support Contractility of Isolated Rat Atria 1

Abstract

Summary

In the absence of exogenous substrate, bicarbonate-free medium produced a marked depressant effect on the force of contraction of isolated rat atria which was not reversed by 20 mM glucose. Since the negative inotropic effects of bicarbonate-free medium are due to an inhibition of phosphofructokinase (PFK) this indicates that endogenous substrate above the PFK step, probably glycogen, is very important for the contractile process, at least in the absence of exogenously supplied substrate. Citrate, another inhibitor of PFK, also produced a marked depressant action on the force of contraction in the absence of exogenous substrate. The nature of its inhibitory effect was different from that produced by bicarbonatefree medium since depression by citrate was partially overcome with 20 mM glucose. Since bicarbonate-free medium did not completely suppress the contractility of the atria, endogenous substrates below the PFK step, probably lipid and/or lactate, besides glycogen, can serve as a source of fuel for the contractile process in substrate-free medium.