PYK2 expression and phosphorylation in neonatal and adult cardiomyocytes

Prolin-rich tyrosine kinase (PYK2) is a Ca2+-dependcnt, non-receptor protein tyrosine kinase involved in growth factor signaling. Although PYK2 is ex-pressed in a variety of tissues, it has not yet been identified in cardiac muscle, Therefore, immunocytochemical and Western blotting techniques were used to examine PYK2 expression and phosphorylation ill neonatal and adult rat ventricular cardiomyocytes (NRVM and ARVM, respectively). PYK2 concentration was much greater in neonatal, than in adult ventricular tissue and cardiomyocytes, In cultured cells, PYK2 expression was highly dependent on [Ca2+](i) transients and contractile activity. Non-contracting, low-density NRVM in serum-free culture expressed very low levels of PYK2. While high-density, spontaneously contracting NRVM showed a similar to 12-fold increase in PYK2 expression. Conversely, high-density NRVM treated with nifedipine (10 muM, 48 h) to block spontaneous [Ca2-](i) transients and contractile activity resulted in a 2.6-fold decrease in PYK2 levels. Similarly, overnight culture of quiescent ARTM I markedly reduced PYK2 levels. Chronic treatment (48 h) of cultured NRVM with the hypertrophic agonist endothelin-1 (10-300 nM) did not significantly increase PYK2 levels, but strongly shifted the ratio of phosphorylated to total PYK2. indicating that PYK2 phosphorylation accompanies cardiomyocyte hypertrophy. Endothelin-1 also acutely activated PYK2 in both cultured NRM. and in freshly isolated ARVM. These results suggest that PYK2 is involved in the generation of certain aspects uf cardiomyocyte hypertrophy. (C) 2001 Academic Press.