Phorbol ester and endothelin-1 alter functional expression of Na+/Ca2+ exchange, K+, and Ca2+ currents in cultured neonatal rat myocytes.
Endothelin-1 (ET-1) and activation of protein kinase C (PKC) have been implicated in alterations of myocyte function in cardiac hypertrophy and heart failure. Changes in cellular Ca2+ handling and electrophysiological properties also occur in these states and may contribute to mechanical dysfunction and arrhythmias. While ET-1 or PKC stimulation induces cellular hypertrophy in cultured neonatal rat ventricular myocytes (NRVMs), a system widely used in studies of hypertrophic signaling, there is little data about electrophysiological changes. Here we studied the effects of ET-1 (100 nM) or the PKC activator phorbol 12-myristate 13-acetate (PMA, 1 μM) on ionic currents in NRVMs. The acute effects of PMA or ET-1 (≤30 min) were small or insignificant. However, PMA or ET-1 exposure for 48-72 h increased cell capacitance by 100 or 25%, respectively, indicating cellular hypertrophy. ET-1 also slightly increased Ca2+ current density (T and L type). Na+/Ca2+ exchange current was increased by chronic pretreatment with either PMA or ET-1. In contrast, transient outward and delayed rectifier K+ currents were strongly downregulated by PMA or ET-1 pretreatment. Inward rectifier K+ current tended toward a decrease at larger negative potential, but time-independent outward K+ current was unaltered by either treatment. The enhanced inward and reduced outward currents also result in action potential prolongation after PMA or ET-1 pretreatment. We conclude that chronic PMA or ET-1 exposure in cultured NRVMs causes altered functional expression of cardiac ion currents, which mimic electrophysiological changes seen in whole animal and human hypertrophy and heart failure.
Cardiovascular Institute and Department of Medicine, Stritch School of Medicine, Loyola University Chicago, Maywood, IL, USA.
José L
JL
Puglisi
Weilong
W
Yuan
Valeriy
V
Timofeyev
Richard E
RE
Myers
Nipavan
N
Chiamvimonvat
Allen M
AM
Samarel
Donald M
DM
Bers
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D015220:Calcium Channels / Q000096:biosynthesis* / Q000187:drug effects; D048429:Cell Size; D002478:Cells, Cultured; D055724:Electrophysiological Phenomena; D019332:Endothelin-1 / Q000494:pharmacology*; D066298:In Vitro Techniques; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D015221:Potassium Channels / Q000096:biosynthesis* / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019831:Sodium-Calcium Exchanger / Q000096:biosynthesis*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D015220:Calcium Channels; D019332:Endothelin-1; D015221:Potassium Channels; D019831:Sodium-Calcium Exchanger; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate