title: Reduction of I(to) causes hypertrophy in neonatal rat ventricular myocytes.
abstract: Prolonged action potential duration (APD) and decreased transient outward K+ current (I(to)) as a result of decreased expression of K(v4.2) and K(v4.3) genes are commonly observed in heart disease. We found that treatment of cultured neonatal rat ventricular myocytes with Heteropoda Toxin3, a blocker of cardiac I(to), induced hypertrophy as measured using cell membrane capacitance and (3)H-leucine uptake. To dissect the role of specific I(to)-encoding genes in hypertrophy, I(to) was selectively reduced by overexpressing mutant dominant-negative (DN) transgenes. I(to) amplitude was reduced equally (by about 50%) by overexpression of DN K(v1.4) (K(v1.4)N) or DN K(v4.2) (either K(v4.2)N or K(v4.2)W362F), but only DN K(v4.2) prolonged APD duration (at 1 Hz) and induced myocyte hypertrophy. This hypertrophy was prevented by coexpressing wild-type K(v4.2) channels (K(v4.2)F) with the DN K(v4.2) genes, suggesting the hypertrophy is due to I(to) reduction and not nonspecific effects of transgene overexpression. The hypertrophy caused by reductions of K(v4.x)-based I(to) was associated with increased activity of the calcium-dependent phosphatase, calcineurin, and could be prevented by coinfection with Ad-CAIN, a specific calcineurin inhibitor. The hypertrophy and calcineurin activation induced by K(v4.2)N infection were prevented by blocking Ca2+ entry and excitability with verapamil or high [K+]o. Our studies suggest that reductions of K(v4.2/3)-based I(to) play a role in hypertrophy signaling by activation of calcineurin.
authors.affiliation: Department of Physiology, Heart and Stroke/Richard Lewar Center, University of Toronto, Toronto, Canada.
authors.forename: Zamaneh
authors.initials: Z
authors.lastname: Kassiri
authors.forename: Carsten
authors.initials: C
authors.lastname: Zobel
authors.forename: The-Tin T
authors.initials: TT
authors.lastname: Nguyen
authors.forename: Jeffery D
authors.initials: JD
authors.lastname: Molkentin
authors.forename: Peter H
authors.initials: PH
authors.lastname: Backx
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000235:genetics; D019943:Amino Acid Substitution; D000818:Animals; D000831:Animals, Newborn; D051017:Apoptosis Regulatory Proteins; D019703:Calcineurin / Q000378:metabolism; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D006332:Cardiomegaly / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology; D002478:Cells, Cultured; D015870:Gene Expression; D005799:Genes, Dominant; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051665:Kv1.4 Potassium Channel; D016297:Mutagenesis, Site-Directed; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D017207:Rats, Sprague-Dawley; D051672:Shal Potassium Channels; D013111:Spider Venoms / Q000494:pharmacology; D019076:Transgenes
chemical_list: D051017:Apoptosis Regulatory Proteins; C113573:Cabin1 protein, rat; D065095:Calcineurin Inhibitors; D002121:Calcium Channel Blockers; D002352:Carrier Proteins; C496979:Kcna4 protein, rat; D051665:Kv1.4 Potassium Channel; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051672:Shal Potassium Channels; D013111:Spider Venoms; D019703:Calcineurin; D011188:Potassium; D002118:Calcium