Cardiac effects of diinosine tetraphosphate, a putative dinucleotide receptor antagonist

The cardiac electrophysiological and vasomotor effects of diinosine tetraph osphate (Ip(4)I, 10 nM and 1 muM) were examined in guinea pig isolated hear ts together with its ability to antagonize the effects oi diadenosine tetra phosphate (Ap(4)A, 1 nM and 1 muM). Ip(4)I had no effects on action potenti al duration or refractory period and attenuated the electrophysiological ef fects of Ap4A at both concentrations. Although Ip(4)I increased coronary pe rfusion pressure, the vasomotor effects of Ap(4)A were resistant to antagon ism by Ip(4)I. These observations support data from neural tissues and indi cate that diinosine polyphosphates may antagonize cardiac electrophysiologi cal effects of diadenosine polyphosphates. (C) 2001 Wiley-Liss, Inc.