| Summary: | 碩士 === 國防醫學院 === 生理學研究所 === 79 === The action potential (AP), twitch tension (TT), and intracellular sodium ion activity (aiNa) were measured simultaneously in isolated canine purkinje fiber and ventricular papillary muscle of guinea pig driven at 60 beats/min. Epinephrine enhanced TT and rate of tension generation, decreased the time to peak tension generation and aiNa in both canine purkinje fiber and guinea pig papillary muscle. purkinje fiber was more sensitive and showed a negative inotropy during recovery. The change of the AP included an elevated plateau a hyperpolarized maximal diastolic potential (MDP) and a prolonged or shortened duration. The maximum rate of upstroke of the action potential was suppressed in purkinje fiber. DBCAMP and forskolin had effects similar to epinephrine including a positive inotropy, an increase of rate of tension generation, a decrease in aiNa and a change of the action potential. Caffeine (3 mM) increased TT and aiNa, prolonged APD and tension duration. The AP showed a pronounced elevation of amplitude and plateau, and an elongated APD with depolarized MDP. ourbain (1 uM) inoreased. aiNa and TT in parallel, lowered amplitude, shortened duration, and depolarized MDP. The results in our study show that epinephrine, forskolin and DBCAMP have a common effect on subcellular level possibly through an augmented ICa, Ik and Na pump. Ouabain and caffeine both increase TT and aiNa that demonstrate the existance of Na+-Ca2+ exchange in regulation of tension generation.
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