Effects of sympathetic nerve stimulation on the sino-atrial node of the XXXX .

@entity840 @entity591 @entity1919 @entity460 @entity594 @entity1063
1. The effects of sympathetic nerve stimulation on the generation of pacemaker action potentials, recorded from the sino-atrial node of the @entity840 , were determined by using intracellular recording techniques. 2. Trains of stimuli applied to the right stellate ganglion led to an increase in heart rate after a delay of a few seconds. During the initial phase of the @entity591 the rate of discharge of pacemaker action potentials increased and the rate of diastolic depolarization increased, but both the peak diastolic potential and the maximum rate of rise of the action potentials were reduced. During the later phase of the @entity591 the peak diastolic potential, the amplitude of the action potentials, the maximum rate of rise and the rate of repolarization of the action potentials were increased. 3. When membrane potential recordings were made from sino-atrial node cells, in which beating had been abolished by adding the organic @entity460 antagonist @entity594 , sympathetic nerve stimulation initiated excitatory junction potentials (EJPs) which had time courses similar to those of the @entity591 recorded from beating preparations. 4. Although both the @entity591 produced by either sympathetic nerve stimulation or added @entity1063 were largely abolished by beta-adrenoceptor antagonists, the membrane potential changes recorded during the responses to sympathetic nerve stimulation or added @entity1063 were different. Bath-applied @entity1063 caused a @entity591 which was associated with an increase in the amplitudes of pacemaker action potentials, an increase in the peak diastolic potential and a shortening in the duration of pacemaker action potentials. 5. The addition of agents which cause the accumulation of @entity1919 in the cytoplasm of the cells produced a @entity591 which was associated with a similar sequence of changes in the membrane potentials to those produced by added @entity1063 ; again the membrane potential changes produced by these agents differed from those produced by sympathetic nerve stimulation. 6. The results are discussed in relation to the idea that neurally released @entity1063 activates a set of receptors which cause @entity591 by increasing inward current flow during diastole, whereas added @entity1063 activates a set of receptors that are linked to a @entity1919 -dependent pathway which modifies the properties of some of the voltage-dependent channels involved in pacemaking activity.
