EFFECTS OF INTRACELLULAR CA2+ CHELATING ON NORADRENALINE RELEASE IN NORMOXIC AND ANOXIC HEARTS

1. Ischaemia and anoxia induce excessive noradrenaline (NA) release in the heart by a mechanism independent of both nerve activity and extra cellular Ca2+, The present study was designed to examine the potential role of intracellular Ca2+ mobilization in anoxic NA release in the h eart by chelating intracellular free Ca2+. 2. In normoxic hearts, prel oading with an intracellular free Ca2+ chelator (BAPTA) reduced neuron al NA release by 65%, confirming the effectiveness of the loading prot ocol, Release of NA independent of nerve activity occurred in hearts s ubjected to a 40 min period of anoxic, substrate-free and nominal Ca2-free perfusion. Loading hearts with BAPTA prior to anoxia failed to r educe NA overflow (1561+/-147 vs 1496+/-206 pmol/g over 40 min), Infus ion with BAPTA (20 mu mol/L) during the first 25 min of the anoxic per iod reduced the quantity of anoxic NA release by approximately 25% fro m 2013+/-124 to 1476+/-207 pmol/g (P<0.05). 3. Our results confirm tha t anoxic NA release is predominantly a Ca2+-independent process with C a2+ mobilization from endogenous storage playing only a minor contribu ting role.