Estimation of survival rate of the spiral ganglion cells by the electrically evoked middle latency responses

학위논문(박사)--서울대학교 대학원 :의학과 이비인후과학전공,1996.Docto

Action of angiotensin II on the vascular smooth muscle in isolated rabbit aorta

The activation mechanism of vascular smooth muscle by angiotensin 11 (A. 11) was studied in isolated aorta. Helical strips of arterial muscle were prepared from the descending thoracic aorta of rabbit. All experiments were performed in HCO-a-buffered Tyrode solution which was aerated with 3% CO,-97% 0, mixed gas and kept at 35°C. In the experiment for the effect of La' on the A. II-induced contraction, however, tris-buffered Tyrode solution aerated wih 100% 0, was used. Contractile response appeared from the concentration of 10-'M A. II, and reached a maximum level at 10-1M A. II. The amplitude of contraction was not altered, if helical strips were exposed repeatedly to A. II for 6 minutes every 30 minutes, showing that there was no tachyphylaxis for the action of angiotensin n. A. II produced a contraction even on the contracture induced by K-depolarization, and also in K· Tyrode solution pretreated with verapamil or La", In Call-free Tyrode solution, A. II induced a contraction, but the contraction was not sustained and decreased gradually. The amplitude of A. n·induced contraction was dependent on external bathing Call: The contraction increased dose-dependently, up to 2 mM Ca", but above that the amplitude was decreasing. The sustained contraction induced by 1O-8M A. II was suppressed significantly by the addition of «-blocker. The results of this experiment suggest that A. IIinduced contraetion was developed by its direct action on the smooth muscle and also the indirect action mediated through the adrenergic endings, and that A. II action is independent of changes in transmembrane potential and associated with promoting both transmembrane Ca*-influx and the mobilization of cellular Ca"

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