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Effects of brief vagal stimulation on the rabbit sinoatrial node activity
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A PROTECTIONMECHANISMOF SINUS NODEPACEMAKER AGAINST STRETCH. A. Kamiyama, H. Sugi Department of Physiology, School of Medicine, Teikyo University, Tokyo, Japan When the spacimens of sinus nodal tissue from rabbit heart were stretched by 50-80% and then held at the stretched length, the pacemaker frequency increased during stretch, and then gradually decreased roughly in parallel with the decay of tension developed by stretch. If, on the other hand, they were stretched by applying constant loads of 5-log, the pacemaker frequency increased by the resulting stretch, and then was found to be maintained at least for 5min. These results suggest that the pacemaker region is surrounded by more compliant tissues, which serve to protect the pacemaker against sudden stretches. The above possibility was proved by recording the length changes at different parts of the spacimen during and after stretch with a 16mmhigh-speed cinecamera at 50-150framesfsec; the perinodal region was always observed to be more compliant than the nodal pacemaker region.
64 EFFECTSOF BRIEF VAGALSTIMULATION ON THE RABBIT SINOJ. Goto, I. Kodama, J. Toyama, ATRIAL NODEACTIVITY. of Environmental Medicine K. Yamada. Research Institute Nagoya, Japan 9 Nagoya University, Phase related effects of vagal stimulation on the rabbit sino-atria1 (S-A) node activity were studied. Impulse trains, subthreshold for excitation of myocardial cells were applied to the S-A node preparation. Transmembrane potentials were recorded by conventional microelectrode techniques. Stimuli delivered at the early portion of phase 4 of a cycle of sinus excitation induced membrane hyperpolarization and prolonged that cycle. Latency of this hyperpolarization was about 80 msec from the onset of the stimulation. Stimuli delivered at the late portion of phase 4 was not effective in prolonging that cycle but effective in prolonging the subsequent cycle. These effects were abolished by atropine. It was suggested that this phase related effects of vagal stimulation might be due to the properties of the muscarinic ACh receptor.
A PROTECTIONMECHANISMOF SINUS NODEPACEMAKER AGAINST STRETCH. A. Kamiyama, H. Sugi Department of Physiology, School of Medicine, Teikyo University, Tokyo, Japan When the spacimens of sinus nodal tissue from rabbit heart were stretched by 50-80% and then held at the stretched length, the pacemaker frequency increased during stretch, and then gradually decreased roughly in parallel with the decay of tension developed by stretch. If, on the other hand, they were stretched by applying constant loads of 5-log, the pacemaker frequency increased by the resulting stretch, and then was found to be maintained at least for 5min. These results suggest that the pacemaker region is surrounded by more compliant tissues, which serve to protect the pacemaker against sudden stretches. The above possibility was proved by recording the length changes at different parts of the spacimen during and after stretch with a 16mmhigh-speed cinecamera at 50-150framesfsec; the perinodal region was always observed to be more compliant than the nodal pacemaker region.
64 EFFECTSOF BRIEF VAGALSTIMULATION ON THE RABBIT SINOJ. Goto, I. Kodama, J. Toyama, ATRIAL NODEACTIVITY. of Environmental Medicine K. Yamada. Research Institute Nagoya, Japan 9 Nagoya University, Phase related effects of vagal stimulation on the rabbit sino-atria1 (S-A) node activity were studied. Impulse trains, subthreshold for excitation of myocardial cells were applied to the S-A node preparation. Transmembrane potentials were recorded by conventional microelectrode techniques. Stimuli delivered at the early portion of phase 4 of a cycle of sinus excitation induced membrane hyperpolarization and prolonged that cycle. Latency of this hyperpolarization was about 80 msec from the onset of the stimulation. Stimuli delivered at the late portion of phase 4 was not effective in prolonging that cycle but effective in prolonging the subsequent cycle. These effects were abolished by atropine. It was suggested that this phase related effects of vagal stimulation might be due to the properties of the muscarinic ACh receptor.