[Effects of dopexamine on the electrophysiologic changes during myocardial ischemia and comparison with fenoldopam...

The effects of dopexamine (DPX), a new dopamine receptor agonist, on transmembrane potential and effective refractory period (ERP) of isolated guinea pig ventricular muscle superfused either with hypoxia or mimic ischemia perfusates were investigated by using intracellular microelectrode technique and compared with fenoldopam (FODA) and procaterol. DPX (3 x 10(-6) mol.L-1) was found to significantly reduce both the extent of decrease of resting potential, action potential amplitude and maximal upstroke velocity and the degree of shortening of action potential duration caused by hypoxia or ischemia. These effects of DPX were significantly greater than those of FODA and procaterol albeit the latter showed effects similar to DPX. DPX could not only lengthen the abbreviated ERP resulting from hypoxia, but also shorten the prolonged ERP caused by ischemia. This action of DPX was more evident than that of FODA and procaterol. The results reveal the potential advantages of DPX over other dopaminergic agonists in the antiarrhythmic activity during myocardial ischemia.