[The arrhythmogenicity of alpha 1-adrenergic stimulation following myocardial acidosis]

Ischemia is associated with myocardial acidosis which recovers upon reperfusion. In such conditions, alpha 1-adrenergic stimulation is arrhythmogenic. We used single cardiac myocytes loaded with the pH fluorescent dye, SNARF-1, to determine if a modulation of pH could explain the effect of alpha 1-adrenergic stimulation. Cells were exposed to acidosis (CO2 15%) for 15 min and then normocapnia restored. During acidosis, alpha 1-adrenergic stimulation caused an increase in pH which was abolished by blocking Na+/H+ exchange with ethylisopropylamiloride (EIPA). After removal of acidosis aftercontractions were manifest in 8 out of 10 and 1 out of 5 cells in the presence of an alpha 1-adrenergic agonist and in control, respectively (p < 0.001). EIPA abolished the occurrence of after contractions. Thus, the arrhythmogenicity of alpha 1-adrenergic stimulation depends on activation of Na+/H+ exchanger.