[The pacemaker cells of the heart: their electrical activity and the effect of autonomic neuromediators].

The review is concerned with mechanisms of rhythmogenesis in pacemaker cells of the heart and with action of autonomic transmitters on these cells. Most attention is paid to background conditions in the action of transmitters and to secondary effects of their influences: on the basis of these background conditions and secondary effects are explained some of the mechanisms of many phenomena associated with neural influences on heart rate (vagal escape, "paradoxical" positive vagal effect, phase-dependent neural influences). Two types of transmitter influences on pacemaker cells are distinguished: the controlling influences and the modulating ones. The controlling influences can serve to set up the heart rate to a strictly determined level, and with the modulating ones only the limits of possible regulation of heart rate can be approximately shifted. The controlling influences are realized through the action of acetylcholine on IAch-channel, sensitive only to that transmitter: on the other hand, the modulating influences are performed through the actions of acetylcholine and catecholamines on voltage-dependent currents determining the rhythmogenesis in pacemaker cells--ICa, IK and Ih. Biochemical mechanisms of the two kinds of influences are discussed; the modulating ones are realized through some second-messenger systems.