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This Article Full Text Full Text (PDF) All Versions of this Article: 294/6/H2540    most recent 00046.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Wang, C. Articles by Wang, H.-C. PubMed PubMed Citation Articles by Wang, C. Articles by Wang, H.-C.

Apelin decreases the SR Ca²⁺ content but enhances the amplitude of [Ca²⁺]_i transient and contractions during twitches in isolated rat cardiac myocytes

Departments of ¹Cardiology and ²Gastrointestinal Surgery, Xi Jing Hospital, the Fourth Military Medical University, Xi'an, People's Republic of China

Submitted 14 January 2008 ; accepted in final form 10 April 2008

Apelin has been reported to have a positive inotropic action in the isolated rat heart. However, the effect of apelin on sarcoplasmic reticulum (SR) Ca²⁺ content and its influence on intracellular Ca²⁺ transient during excitation-contraction coupling remains poorly understood. In the present study, we determined the effect of apelin on Ca²⁺ transient and contractions in isolated rat cardiomyocytes. When compared with control, treatment with apelin caused a 55.7 ± 13.9% increase in sarcomere fraction shortening and a 43.6 ± 4.56% increase in amplitude of electrical-stimulated intracellular Ca²⁺ concentration (E[Ca²⁺]_i) transients (n = 14, P < 0.05). But SR Ca²⁺ content measured by caffeine-induced [Ca²⁺]_i (C[Ca²⁺]_i) transient was decreased 8.41 ± 0.92% in response to apelin (n = 14, P < 0.05). Na⁺/Ca²⁺ exchanger (NCX) function was increased since half-decay time of C[Ca²⁺]_i was decreased 16.22 ± 1.36% in response to apelin. Sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) activity was also increased by apelin. These responses can be partially or completely blocked by chelerythrine chloride, a PKC inhibitor. In addition, to confirm our data, we used indo-1 as another Ca²⁺ indicator and rapid cooling as another way to measure SR Ca²⁺ content, and we observed similar results. So we conclude that apelin has a 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.

excitation-contraction coupling; intracellular calcium concentration; positive inotropic action; protein kinase C; sarcoplasmic reticulum