Effects of acetaldehyde on membrane potentials of sinus node pacemaker fibers

The experiments reported here were performed to characterize the effects of acetaldehyde on membrane potentials (MP) of sinus node subsidiary pacemaker fibers in the absence and presence of adrenergic and cholinergic blockade. Guinea pig sinoatrial preparations were superfused with Tyrode's solution at 37 degrees C while electrically stimulated at 5 Hz. Intracellular microelectrodes were used to record the MP of sinus node subsidiary pacemaker fibers. Acetaldehyde 3 x 10(-6) M and 3 x 10(-3) M had no effect on maximum diastolic potential (MDP), while 3 x 10(-5) M and 3 x 10(-2) M exerted a depolarizing effect on the MDP, without affecting the overshoot (OS). The fall in MDP was associated with a reduction in the amplitude of the action potential (AAP) and the maximum velocity of phase 0 (Vmax 0). The depressant effect of acetaldehyde on MDP was not abolished by adrenergic blockers or atropine. Concentrations of acetaldehyde between 3 x 10(-5) and 3 x 10(-2) M prolonged the action potential duration (APD). Acetaldehyde 3 x 10(-3) M did not affect MDP even in the presence of atropine or propranolol. The APD-prolonging effect of acetaldehyde was not abolished by adrenergic blockers. In summary, the actions of acetaldehyde on MDP and APD were independent of adrenergic and cholinergic mechanisms.