13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

RT-52

Arrhythmogenic actions of norepinephrine and acetylcholine in sheep cardiac purkinje fibers

Ennio Aceto, Mario Vassalle.
Department of Physiology, State University of New York, New York, USA

This work was supported by a grant from the Am Heart Association, NY Affiliate.

Introduction

It is well known that in the sino-atrial node, norepinephrine (NE) has excitatory actions, whereas acetylcholine (ACh) has inhibitory actions. In addition, the inhibitory effects of ACh prevail over the excitatory actions of NE. However, these findings do not necessarily apply to other cardiac pacemakers, since ACh can induce spontaneous activity in sheep Purkinje fibers that are either quiescent¹ or have been driven (overdrive excitation)². Both neuromediators affect the activity of the Na⁺-K⁺ pump (Na pump), but NE stimulates³ and ACh may inhibit¹ it. Since the Na pump creates an outward current⁴, a change in its activity may shift DD away from or toward the threshold.

The aim of the present experiments was to study in sheep cardiac Purkinje fibers the actions of NE and ACh (singly and together) on spontaneous activity and on drive patterns to determine modalities and mechanisms of the changes induced. Tests were also carried in low and high [Ca²⁺]_o.