[Peripheral mechanisms of vagal sinus arrhythmia: a role of typical affiliation of cardiac M-cholinoreceptors]

Abstract

Salvo impulses on the vagus nerve of a cat with a varying in each cardiocycle interval after ECG P wave led to recurrent variations of ECG interval P-P manifesting as sinus arrhythmia. A chronotropic effect of the vagus nerve experienced moderate changes in dislocation of the vagus stimulus position in the beginning of cardiocycle lasting about 200 ms after ECG P wave and in ECG segment T-P. Distinct (in the range 100-300 ms) variations of the interval ECG P-P lengthening took place in the change of the vagus stimulus generation moment in the narrow zone of cardiocycle of 40-70 ms duration. The zone location corresponded to the end of ECG T wave. Metoctramine or gallamine block of M2-cholinoreceptors reduced maximal lengthening of the interval P-P and severity of cycle changes of P-P interval in arrhythmia and its variation amplitude under changing moment of vagus stimulus generation in the zone of cardiocycle showing marked shifts of a chronotropic effect. M1-cholinoreceptor block with pirenzepin or receptors of M3-subtype in the action of 4-DAMP produced an opposite effect enhancing these parameters.