CHOLINESTERASE AFFECTS DYNAMIC TRANSDUCTION PROPERTIES FROM VAGAL-STIMULATION TO HEART-RATE

Recent investigations in our laboratory using a Gaussian white noise t echnique showed that the transfer function representing the dynamic pr operties of transduction from vagus nerve activity to heart rate had c haracteristics of a first-order low-pass filter. However, the physiolo gical determinants of those characteristics remain to be elucidated. I n this study, we stimulated the vagus nerve according to a Gaussian wh ite noise pattern to estimate the transfer function from vagal stimula tion to the heart rate response in anesthetized rabbits and examined h ow changes in acetylcholine kinetics affected the transfer function. W e found that although increases in the mean frequency of vagal stimula tion from 5 to 10 Hz did not change the characteristics of the transfe r function, administration of neostigmine (30 mu g . kg(-1) . h(-1) iv ), a cholinesterase inhibitor, increased the dynamic gain from 8.19 +/ - 3.66 to 11.7 +/- 4.88 beats . min(-1) . Hz(-1) (P < 0.05), decreased the corner frequency from 0.12 +/- 0.05 to 0.04 +/- 0.01 Hz (P < 0.01 ), and increased the lag time from 0.17 +/- 0.12 to 0.27 +/- 0.08 s (P < 0.05). These results suggest that the rate of acetylcholine degrada tion at the neuroeffector junction, rather than the amount of availabl e acetylcholine, plays a key role in determining the dynamic propertie s of transduction from vagus nerve activity to heart rate.