Effects of acetaldehyde on the automaticity of the guinea pig sinus node.

The objective of this investigation was to characterize the effects of acetaldehyde (ACA) on sinus node automaticity (SNA). Guinea pig sinoatrial preparations superfused with Tyrode's solution at 37 degrees C were used. Intracellular microelectrodes were used to monitor SN rate (SNR). Acetaldehyde 3 X 10(-5) M had no effect on SNR, while 3 X 10(-3) M had a positive chronotropic action. The increase in SNR was associated with an increase in the slope of the slow diastolic depolarization (SDD) of subsidiary pacemaker fibers, with no change in the maximum diastolic potential (MDP). Acetaldehyde 3 X 10(-2) M exerted a biphasic effect: the SNR was enhanced and then depressed. Propranolol blocked the positive component of this chronotropic action. The negative component was not modified by propranolol, phentolamine, or atropine. It is concluded that ACA exerts both positive and negative chronotropic actions on the guinea pig sinus node. The positive component of this biphasic effect is mediated through a beta-adrenergic mechanism and it is associated with an increase in the SDD. The negative component is not due to alpha- or beta-adrenergic or muscarinic stimulation.