Submitted on January 14, 2008
Revised on March 31, 2008
Accepted on April 10, 2008
Apelin Decreases the SR Ca2+ Content but Enhances the Amplitude of [Ca2+]i Transient and contractions during Twitches in Isolated Rat Cardiac Myocytes
Chen Wang, Jun-Feng Du, Feng Wu, and Hai-Chang Wang1*
1 Department of cardiology, Xijing Hospital, FMMU
* To whom correspondence should be addressed. E-mail: wanghc{at}fmmu.edu.cn.
Apelin has been reported to have a positive inotropic action in the isolated rat heart. However, the effect of apelin on SR Ca2+ content and its influence on intracellular Ca2+ transient during excitation-contraction (E-C) coupling remains poorly understood. In the present study, we determined the effect of apelin on Ca2+ transient and contractions in isolated rat cardiomyocytes. Compared with control, treatment with apelin caused a 55.7±13.9% increase in sarcomere fraction shortening (FS) and a 43.6±4.56% increase in amplitude of E[Ca2+]i transients (n=14,P<0.05). But SR Ca2+ content measured by caffeine-induced Ca2+ ([Ca2+]i) transient was decreased 8.41±0.92% in response to apelin (n=14,P<0.05). NCX function was increased since half-decay time (T50) of C[Ca2+]i was decreased 16.22±1.36% in response to apelin. Sarcoplasmic reticulum Ca2+-ATPase (SERCA) activity was also increased by apelin. These responses can be partially or completely blocked by chelerythrine chloride (CHE), a PKC inhibitor. In addition, to confirm our data, we used indo-1 as another Ca2+ indicator and rapid cooling(RC) as another way to measure SR Ca2+ content, and we got the similar results. So we conclude that apelin has positive inotropic effect on isolated myocytes, and increased amplitude of E[Ca2+]i is at least partially involved in the mechanism. NCX function and SERCA activity are increased by apelin, and the SR Ca2+ content is decreased by apelin during twitches. PKC played an important role in these signaling mechanisms.
