- 作者: Jung-Mou Yang kou-Toung chung Shuh-Tsong Yang zSan-Nan Yang
- 作者服務機構: Department of Physiology and Biophysics, National Defense Medical Center, Taipei, Taiwan, ROC
- 中文摘要: --
- 英文摘要: In this study, the effects of carbachol(CCh)on twitch ten-sion, intracellular Na activity(a ), and action potentialwere simultaneously measured in canine cardiac Pur-kinje fibers in orderto examine the regulation of inotropythrough muscarinic receptors and its relation to a . Infibers driven at 1 Hz, CCh(10μM) initially and transientlydecreased and then increased the twitch tension by 36±8%. The action potential showed a significant elevationof the plateau and a significant shortening of the dura-tion at 90%repolarization (APD ), from 403±7 to 389±7 ms. The a decreased from 7.4±0.4 to 6.7±0.3 mM(n=23, p<0.05). Atropine(1μM)decreased the twitchtension by 21±6%(n=7, p<0.05) without significanteffects on the action potential and a , and inhibited theeffects of CCh. Cs (20 mM)increased the plateau heightand APD9o, enhanced the twitch tension by 66±24%,but decreased aiNa from 7.3±0.3 to 6.3±0.4 mM(n=6,p<0.05). In the presence of 20 mM Cs , some fibers gen-erated slow responses. The addition of 10 pM CCh fur-ther increased the twitch tension and APD , and de-creased a from 6.3±0.4 to 5.3±0.3 mM. Ouabain(0.3μM)increased the twitch tension and a , and inhib-ited the CCh-induced decrease of a .In the presence ofouabain, 20 mM Cs depolarized the fiber and generatedslow responses with a decreased a . The addition of10μM CCh enhanced the slow action potential, andincreased a although there was a transient decreaseduring early exposure. These results suggest that activa-tion of muscarinic receptors in canine Purkinje fibersresults in an enhancement of the Na -K pump activityand a biphasic inotropic response, probably via differentreceptor subtypes. The inhibitory effect, most likelythrough M receptors, is associated with the activation ofK channels. The stimulatory effect, on the other hand, isprobably due to the action on the M, receptors, resultingin increases in Caz+currents.
- 中文關鍵字: --
- 英文關鍵字: Purkinje fiber. Muscarinic Receptor. Na+, cellular