1. Genistein is a tyrosine kinase inhibitor which interferes with the activity of several ionic channels either by altering modulatory phosphorylating processes or by direct binding. In whole-cell conditions, genistein induces a partial inhibition of the pacemaker (I f) current recorded in cardiac sinoatrial and ventricular myocytes. 2. We investigated the mechanism of action of genistein (50 μM) on the I f current in whole-cell, cell-attached, and inside-out configurations, and the measured fractional inhibitions were similar: 26.6, 27.2, and 33.6%, respectively. 3. When ATP was removed from the whole-cell pipette solution no differences were revealed in the effect of the drug when compared to metabolically active cells. Genistein fully maintained its blocking ability even when herbimycin, a tyrosine kinase inhibitor, was added to the whole-cell ATP-free pipette solution. 4. Genistein-induced block was independent of the gating state of the channel and did not display voltage or current dependence; this independence distinguishes genistein from all other f-channel blockers. 5. When inside-out experiments were performed to test for a direct interaction with the channel, genistein, superfused on the intracellular side of the membrane, decreased the maximal I f conductance, and slightly shifted the current-activation curve to the left. Furthermore, the effect of genistein was independent of cAMP modulation. 6. We conclude that, in addition to its tyrosine kinase-inhibitory properties, genistein also blocks I f by directly interacting with the channel, and thus cannot be considered a valuable pharmacological tool to investigate phosphorylation-dependent modulatory pathways of the I f current and of cardiac rhythm.
|Titolo:||Direct inhibition of the pacemaker (If) current in rabbit sinoatrial node cells by genistein|
FERRONI, ARNALDO (Penultimo)
BARUSCOTTI, MIRKO (Ultimo)
|Settore Scientifico Disciplinare:||Settore BIO/09 - Fisiologia|
|Data di pubblicazione:||2006|
|Digital Object Identifier (DOI):||10.1038/sj.bjp.0706433|
|Appare nelle tipologie:||01 - Articolo su periodico|