AJP - Heart and Circulatory Physiology, Vol 256, Issue 1 74-H84, Copyright © 1989 by American Physiological Society
Role of acetylcholine in induction of repetitive activity in human atrial fibers
Z. Y. Hou, C. I. Lin, M. Vassalle, B. N. Chiang and K. K. Cheng
Department of Medicine, Veterans General Hospital, Taipei, Republic of China.
The actions of acetylcholine and its interactions with epinephrine were
studied in human atrial tissues by recording transmembrane potentials and
contractile force. Acetylcholine (0.55-5.5 microM) reduced force, shortened
the duration and shifted to more negative values the plateau of action
potentials, abolished phase 4 depolarization, and suppressed the activity
of spontaneous fibers. During the recovery, often there was a rebound
increase in some parameters of the action potential and in force.
Epinephrine (0.3-2.8 microM) induced oscillatory potentials and
aftercontractions and acetylcholine abolished them. However, during the
washout of acetylcholine in the presence of epinephrine, the oscillatory
potentials and aftercontractions were larger than before acetylcholine, and
repetitive activity was often induced. The inhibitory and excitatory
effects of acetylcholine were mimicked by methacholine (5.1 microM) and
abolished by atropine (1.5 microM). The postacetylcholine rebound was also
potentiated by theophylline (0.6-2 mM) but was not blocked by propranolol
(1-3.4 microM), prazosin (1 microM), and diltiazem (0.1 microM). It is
concluded that in human atrial fibers acetylcholine has inhibitory as well
as excitatory effects that are exaggerated in the presence of epinephrine
and are mediated by the activation of the muscarinic receptor. The
interaction between acetylcholine and epinephrine involves an antagonism at
an intracellular level.
