Phosphatidylinositol-bisphosphate regulates intercellular coupling in cardiac myocytes.
Changes in the lipid composition of cardiac myocytes have been reported during cardiac hypertrophy, cardiomyopathy, and infarction. Because a recent study indicates a relation between low phosphatidylinositol-bisphosphate (PIP(2)) levels and reduced intercellular coupling, we tested the hypothesis that agonist-induced changes in PIP(2) can result in a reduction of the functional coupling of cardiomyocytes and, consequently, in changes in conduction velocity. Intercellular coupling was measured by Lucifer Yellow dye transfer in cultured neonatal rat cardiomyocytes. Conduction velocity was measured in cardiomyocytes grown on microelectrode arrays. Intercellular coupling was reduced by angiotensin II (43.7 +/- 9.3%, N = 11) and noradrenaline (58.0 +/- 10.7%, N = 11). To test if reduced intercellular coupling after agonist stimulation was caused by PIP(2)-depletion, myocytes were stimulated by angiotensin II (57.3 +/- 5.7%, N = 14) and then allowed to recover in medium with or without wortmannin (an inhibitor of PIP(2) synthesis). Intercellular coupling fully recovered in control medium (102.1 +/- 8.9%, N = 10), whereas no recovery occurred in the presence of wortmannin (69.3 +/- 7.8%, N = 12). Inhibition of PKC, calmodulin, or arachidonic acid production did not affect the response to either angiotensin II or noradrenaline. Furthermore, decreasing or increasing PIP(2) also decreased and increased intercellular coupling, respectively. This supports the role of PIP(2) in the regulation of intercellular coupling. In beating myocytes, conduction velocity was reduced by angiotensin II stimulation, and recovery after wash out was prevented by inhibition of PIP(2) production. Reductions in PIP(2) inhibit intercellular coupling in cardiomyocytes, and stimulation by physiologically relevant agonists reduces intercellular coupling by this mechanism. The reduction in intercellular coupling lowered conduction velocity.
Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.
Johannes P
JP
Hofgaard
Kathrin
K
Banach
Sarah
S
Mollerup
Helene Korvenius
HK
Jørgensen
Søren Peter
SP
Olesen
Niels-Henrik
NH
Holstein-Rathlou
Morten Schak
MS
Nielsen
D000730:Androstadienes / Q000494:pharmacology; D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D016718:Arachidonic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002450:Cell Communication / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism*; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D000077191:Wortmannin
D000730:Androstadienes; D018129:Phosphatidylinositol Phosphates; D047428:Protein Kinase Inhibitors; D044140:Receptor, Angiotensin, Type 1; D018342:Receptors, Adrenergic, beta-1; D000804:Angiotensin II; D016718:Arachidonic Acid; D011493:Protein Kinase C; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D002118:Calcium; D009638:Norepinephrine; D000077191:Wortmannin