Effects of nicotine on automaticity of sinoatrial node in rabbit heart

The electro-physiological effects of nicotine on sinoatrial node cells in rabbit heart were studied using intracellular microelectrodes. When superfused with nicotine 604.0, 60.4, 6.0 or 0.6 mumol/L the spontaneous rate stopped or decreased for 20 s and then increased, eventually surpassing the control values 50 +/- 13, 45 +/- 12, 23 +/- 10 and 14 +/- 6%, respectively. The inhibitory phase was blocked by atropine and the excitatory phase was eliminated by tubocurarine chloride, hexamethonium bromide or pindolol. These results suggest that the effects observed may be related to cholinergic system and caused by nicotine induced catecholamine release.