Accentuated antagonism in vagal heart rate control mediated through muscarinic potassium channels.
Although muscarinic K(+) (K(ACh)) channels contribute to a rapid heart rate (HR) response to vagal stimulation, whether background sympathetic tone affects the HR control via the K(ACh)channels remains to be elucidated. In seven anesthetized rabbits with sinoaortic denervation and vagotomy, we estimated the dynamic transfer function of the HR response by using random binary vagal stimulation (0-10 Hz). Tertiapin, a selective K(ACh) channel blocker, decreased the dynamic gain (to 2.3+/- 0.9 beats.min(-1).Hz(-1), from 4.6+/- 1.1, P < 0.01, mean+/- SD) and the corner frequency (to 0.05+/- 0.01 Hz, from 0.26+/- 0.04, P < 0.01). Under 5 Hz tonic cardiac sympathetic stimulation (CSS), tertiapin decreased the dynamic gain (to 3.6+/- 1.0 beats.min(-1).Hz(-1), from 7.3+/- 1.1, P < 0.01) and the corner frequency (to 0.06+/- 0.02 Hz, from 0.23+/- 0.06, P < 0.01). Two-way analysis of variance indicated significant interaction between the tertiapin and CSS effects on the dynamic gain. In contrast, no significant interactions were observed between the tertiapin and CSS effects on the corner frequency and the lag time. In conclusion, although a cyclic AMP-dependent mechanism has been well established, an accentuated antagonism also occurred in the direct effect of ACh via the K(ACh) channels. The rapidity of the HR response obtained by the K(ACh) channel pathway was robust during the accentuated antagonism.
Department of Cardiovascular Dynamics, Advanced Medical Engineering Center, National Cardiovascular Center Research Institute, Osaka, Japan. m-mizuno@ri.ncvc.go.jp
Masaki
M
Mizuno
Atsunori
A
Kamiya
Toru
T
Kawada
Tadayoshi
T
Miyamoto
Shuji
S
Shimizu
Toshiaki
T
Shishido
Masaru
M
Sugimachi
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001514:Bee Venoms / Q000494:pharmacology; D004558:Electric Stimulation; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D011976:Receptors, Muscarinic / Q000378:metabolism*; D013564:Sympathetic Nervous System / Q000502:physiology; D013997:Time Factors; D014628:Vagotomy; D014630:Vagus Nerve / Q000187:drug effects / Q000378:metabolism*
D001514:Bee Venoms; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011976:Receptors, Muscarinic; C029738:tertiapin; D000109:Acetylcholine