Responses to sympathetic drugs in the ammocoete heart: Probable influence of the small intensely fluorescent (SIF) cells

Abstract

We analysed overflow of catecholamines from ammocoete heart and the action of sympathetic drugs on the superfused ventricle. Experiments were carried out on spontaneously beating and electrically driven ventricular strips. This was done to examine the possible role of small intensely fluorescent cells in lamprey heart. Large adrenaline content in and overflow from auricle and ventricle were observed. Reserpine and adrenergic inhibitors had powerful negative chronotropic and inotropic effects. Tyramine had tachyphylactic chronotropic effects, a reserpine-sensitive positive effect at low concentrations and a negative one at high concentrations. Isoprenaline, neosynephrine, adrenaline and noradrenaline had only a weak action in standard saline solution. However, positive chronotropic and inotropic effects could be recorded after reserpine treatment and in modified saline solutions, particularly in low Ca 2+ ones. Uptake inhibitors were not efficient. Our results show (1) a tyramine-induced release and a large spontaneous release of adrenaline from the small intensely fluorescent cells in lamprey heart and (2) the occurrence of beta and perhaps alpha-adrenoceptors in the myocardium. The weak actions of exogenous catecholamines are likely to be related to the large basal release of adrenaline as the powerful effects of reserpine and adrenergic inhibitors are.