J Mol Cell Cardiol 32, 2349–2359 (2000) doi:10.1006/jmcc.2000.1265, available online at http://www.idealibrary.com on Regional Expression of Protein Phosphatase Type 1 and 2A Catalytic Subunit Isoforms in the Human Heart Hartmut Lu ¨ ss 1 , Oliver Klein-Wiele 1 , Peter Boknı ´k 1 , Stefan Herzig 3 , Jo ¨rg Knapp 1 , Bettina Linck 1 , Frank U. Mu ¨ ller 1 , Hans H. Scheld 2 , Christof Schmid 2 , Wilhelm Schmitz 1 and Joachim Neumann 1 1 Institut fu ¨r Pharmakologie und Toxikologie and 2 Klinik und Poliklinik fu ¨r Herz-, Thorax- und Gefa ¨ßchirurgie, Westfa ¨lische Wilhelms-Universita ¨t Mu ¨nster, Germany, 3 Institut fu ¨r Pharmakologie, Universita ¨t Ko ¨ln, Germany (Received 17 March 2000, accepted in revised form 22 September 2000, published electronically 2 November 2000) H. L ¨ , O. K-W,P.Bı ´, S. H, J. K, B. L, F. U. M ¨ , H. H. S, C. S, W. S J. N. Regional Expression of Protein Phosphatase Type 1 and 2A Catalytic Subunit Isoforms in the Human Heart. Journal of Molecular and Cellular Cardiology (2000) 32, 2349–2359. In mammalian species, including man, the duration of myocardial contraction is shorter in atria than ventricles. Total contraction time depends at least in part on phosphorylation and dephosphorylation of cardiac regulatory proteins. De- phosphorylation reactions are mediated by protein phosphatases. In the mammalian heart more than 90% of the protein phosphatase (PP) activity consists of PP1 and PP2A. Therefore, the aim of this study was to investigate which isoforms of PP1 and PP2A are present in human myocardium and whether their expression is regionally different. RT-PCR and Northern blotting revealed that all isoforms of PP1 and PP2A presently known are expressed in the human heart. Expression levels of PP1, , and as well as 2A were higher in right ventricles than in right atria. However, there was no such difference for PP2A. At the protein level PP1 was unchanged, whereas PP2A was by 56% higher in right ventricles compared to atria. The phosphorylation state of TnI was lower in right ventricle than in right atrium. Thus, lower protein expression of PP2A in atrium could contribute to the faster relaxation by increasing the phosphorylation state of TnI. We conclude that expression of PP1 and PP2A isoforms is regionally regulated in the human heart. 2000 Academic Press K W: Atrium; Calcium; Contractility; Gene expression; Human; Isoforms; Phospholamban; Phospho- protein phosphatases; Sarcoplasmic reticulum; Inhibitory subunit of troponin; Ventricle. than 90% of the protein phosphatase (PP) activity Introduction consists of PP1 and PP2A. 2,3 These PPs regulate myocardial contractile function: for instance The initiation of myocardial contraction depends on the rapid increase in intracellular cytosolic free PP1 and PP2A can dephosphorylate myocardial phospholamban, a regulatory phosphoprotein. 3,4 calcium (Ca 2+ ) during the systole. Relaxation is determined by the velocity of diastolic re-uptake of its dephosphorylated form phospholamban inhibits the activity of the sarco-endoplasmic Ca 2+ into the sarcoplasmic reticulum (SR). Both processes are regulated by phosphorylation and reticulum calcium ATPase 2a (SERCA), leading to diminished diastolic re-uptake of Ca 2+ into dephosphorylation of cardiac regulatory proteins. 1 Dephosphorylation reactions are catalyzed by pro- the SR. 5 Thus, the duration of contraction is prolonged when phospholamban is dephosphory- tein phosphatases. In the mammalian heart more Please address all correspondence to: Hartmut Lu ¨ ss, Institut fu ¨r Pharmakologie und Toxikologie, Westfa ¨lische Wilhelms-Universita ¨t Mu ¨ nster, Domagkstraße 12, D-48149 Mu ¨nster, Germany. E-mail: luss@uni-muenster.de 0022–2828/00/122349+11 $35.00/0 2000 Academic Press