Apelin decreases the SR Ca2+ content but enhances the amplitude of [Ca2+]i transient and contractions during twitches in isolated rat cardiac myocytes.
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.
Wang
Chen
C
Department of Cardiology, Xi Jing Hospital, the Fourth Military Medical University, Xi'an, People's Republic of China.
Du
Jun-Feng
JF
Wu
Feng
F
Wang
Hai-Chang
HC
D000818:Animals; D053119:Benzophenanthridines / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D048429:Cell Size; D003080:Cold Temperature; D004558:Electric Stimulation; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D013997:Time Factors
D053119:Benzophenanthridines; D036341:Intercellular Signaling Peptides and Proteins; D047428:Protein Kinase Inhibitors; D019831:Sodium-Calcium Exchanger; D002110:Caffeine; C016299:chelerythrine; D011493:Protein Kinase C; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases