title: PP2 prevents β-adrenergic stimulation of cardiac pacemaker activity.
abstract: One of the main strategies for cancer therapy is to use tyrosine kinase inhibitors for inhibiting tumor proliferation. Increasing evidence has demonstrated the potential risks of cardiac arrhythmias (such as prolonged QT interval) of these drugs. We report here that a widely used selective inhibitor of Src tyrosine kinases, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), can inhibit and prevent β-adrenergic stimulation of cardiac pacemaker activity. First, in dissected rat sinus node, PP2 inhibited and prevented the isoproterenol-induced increase of spontaneous beating rate. Second, in isolated rat sinus node myocytes, PP2 suppressed the hyperpolarization-activated "funny" current (traditionally called cardiac pacemaker current, I(f)) by negatively shifting the activation curve and decelerating activation kinetics. Third, in isolated rat sinus node myocytes, PP2 decreased the Src kinase activity, the cell surface expression, and tyrosine phosphorylation of hyperpolarization-activated, cyclic nucleotide-modulated channel 4 (HCN4) channel proteins. Finally, in human embryonic kidney 293 cells overexpressing recombinant human HCN4 channels, PP2 reversed the enhancement of HCN4 channels by isoproterenol and inhibited 573x, a cyclic adenosine momophosphate-insensitive human HCN4 mutant. These results demonstrated that inhibition of Src kinase activity in heart by PP2 decreased and prevented β-adrenergic stimulation of cardiac pacemaker activity. These effects are mediated, at least partially, by a cAMP-independent attenuation of channel activity and cell surface expression of HCN4, the main channel protein that controls the heart rate.
authors.affiliation: *Center for Cardiovascular and Respiratory Science, and †Department of Physiology and Pharmacology, West Virginia University, Morgantown, WV; ‡Graduate Institute of Biotechnology, Chinese Culture University, Taipei, Taiwan; §Mary Babb Randolph Cancer Center and ¶Department of Neurobiology and Anatomy, West Virginia University, Morgantown, WV; and ‖Heart Institute of Health Sciences Center, West Virginia University, Morgantown, WV. J. Huang is now with the Department of Neurology, and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT; and Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT.
authors.forename: Jianying
authors.initials: J
authors.lastname: Huang
authors.forename: Yen-Chang
authors.initials: YC
authors.lastname: Lin
authors.forename: Stan
authors.initials: S
authors.lastname: Hileman
authors.forename: Karen H
authors.initials: KH
authors.lastname: Martin
authors.forename: Robert
authors.initials: R
authors.lastname: Hull
authors.forename: Han-Gang
authors.initials: HG
authors.lastname: Yu
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D057809:HEK293 Cells; D006801:Humans; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000096:biosynthesis; D009124:Muscle Proteins / Q000096:biosynthesis; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology; D015221:Potassium Channels / Q000096:biosynthesis; D011743:Pyrimidines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012849:Sinoatrial Node / Q000187:drug effects* / Q000201:enzymology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C412373:AG 1879; D000318:Adrenergic beta-Agonists; C119587:HCN4 protein, human; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D009124:Muscle Proteins; D015221:Potassium Channels; D011743:Pyrimidines; D019061:src-Family Kinases