ADENOSINE INHIBITS THE L-TYPE CALCIUM CURRENT IN HUMAN ATRIAL MYOCYTES

The effects of adenosine on the L-type Ca2+ current (I-Ca) were studie d in human atrial myocytes using the whole-cell voltage clamp techniqu e. I-Ca was recorded under physiological calcium concentrations (1.8 m mol/l) at 37 degrees C. Under these conditions the current density of basal I-Ca averaged 4.0 pA/pF. Isoprenaline (1 mu mol/l) increased bas al I-Ca to 249.7%. Adenosine (100 mu mol/l) in the presence of isopren aline (1 mu mol/l) decreased I-Ca from the level obtained with isopren aline to 87.5% of basal I-Ca Adenosine (0.1 to 100 mu mol/l) also redu ced basal I-Ca, maximally to 64.5% of control. Activation and inactiva tion parameters of basal I-Ca were not significantly different between adenosine (100 mu mol/l) and control recordings. Our results show tha t adenosine affects both basal and isoprenaline stimulated I-Ca in hum an atrial myocytes. Although a considerable decrease of basal I-Ca was seen, we conclude that the action of adenosine on L-type Ca2+ current in human atrial myocytes is mainly antiadrenergic. Both effects may c ontribute to the antiarrhythmic properties of adenosine.