ABSTRACT
Spontaneous slow action potentials of aortic vestibule of isolated guinea pig heart were intracellularlly recorded. Electrophysiological parameters examined are: maximal diastolic potential (MDP), amplitude of action potential (APA), maximal rate of depolarization of phase 0 (V(max)), velocity of diastolic depolarization of phase 4 (VDD), duration of 50% and 90% repolarization (APD(50) and APD(90)) and rate of pacemaker firing (RPF). It was found that (1) 0.5 micromol/L nisoldipine (Nis) significantly decreased APA, V(max), VDD and RPF (P<0.01); (2) 1.2 mmol/L tetrodotoxin (TTX) significantly decreased APA and V(max) (P<0.05), but VDD and RPF were significantly slowed down as compared with control (P<0.01); (3) 2 mmol/L 4-aminopyridine (4-AP) elicited a decrease in MDP, APA and V(max) (P<0.01), but an increase in VDD and RPF (P<0.01); (4) when 1.5 mmol/L CsCl was perfused for 5 min, the VDD and RPF were significantly decreased (P<0.05); and (5) under the condition of hypoxia and perfusion with deprived glucose content for 15 min, the VDD and RPF were decreased (P<0.01). The above results suggest that (1) in addition to Ca(2+), Na(+) current contributes to generation of 0 phase of depolarization of slow response activity in aortic vestibule mainly, and (2) in addition to the inward Ca(2+) and Na(+) current and attenuated K(+) current, I(f) current also plays some role in phase 4 of depolarization.
Subject(s)
Calcium Channels/metabolism , Sodium Channels/metabolism , Taurine/analogs & derivatives , Taurine/physiology , Acamprosate , Action Potentials , Animals , Calcium/metabolism , Female , Guinea Pigs , In Vitro Techniques , Male , Potassium/metabolism , Sodium/metabolismABSTRACT
The automatic activity of aortic vestibule was studied in 82 guinea-pig heart preparations with intracellular microelectrode. Spontaneous activity could be recorded in 16 preparations (19.5%), while in 61 preparations (74.4%) automatic activity could be induced by electrical stimulation. Of these preparations, they were all found a very small region below the right and the poster valves, the response showed a slow and low rising phase and a marked spontaneous depolarization in phase 4. The response could be blocked by Mn2+ and nifedipine. Outside of the specialized valve region, all recorded vestibule action potentials pertain to the fast type. Light and electron microscopic examination showed that the structure of the specialized local aortic vestibule region was similar to that of ordinary myocardium possessing slow automatic activity instead of the ordinary ventricular musculature.
Subject(s)
Aorta, Thoracic/anatomy & histology , Aorta, Thoracic/physiology , Action Potentials/drug effects , Animals , Electric Stimulation , Female , Guinea Pigs , Male , Microelectrodes , Nifedipine/pharmacologyABSTRACT
The effect of atrial natriuretic factor (ANF) on sinoatrial (SA) node cells in guinea pig heart was studied by using intracellular microelectrodes. When the heart superfused with ANF 0.025 and 0.05 mumol/L for 7 min respectively, the spontaneous rate showed no significant changes, but 0.1 mumol/L ANF resulted in a definite decrease by 7% (P less than 0.01). However, when ANF (0.025, 0.05 and 0.1 mumol/L) was superfused along with 0.5 mumol/L isoproterenol, the spontaneous rate was respectively depressed by 4, 12 and 22%. These results indicate that ANF can depress the positive chronotropic effect of isoproterenol. The mechanism of this action may be related to the blocking effect of ANF on T-type calcium channel of SA node.
