Participation of PI3K and atypical PKC in Na1-K1-pump stimulation by IGF-I in VSMC

Li, Dailin, Gary Sweeney, Qinghua Wang, and Amira Klip. Participation of PI3K and atypical PKC in Na1-K1pump stimulation by IGF-I in VSMC. Am. J. Physiol. 276 (Heart Circ. Physiol. 45): H2109–H2116, 1999.—The activity of the Na1-K1-pump is intricately linked to the maintenance of vascular tone. Here we demonstrate that insulin-like growth factor I (IGF-I) increases Na1-K1-pump activity in the vascular smooth muscle cell (VSMC) clone A7r5 in a timeand dose-dependent manner. This stimulatory effect of IGF-I was prevented by the tyrosine kinase inhibitor genistein (5 μM) and by the specific phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin (100 nM) and LY-294002 (25 μM). IGF-I activated a wortmannin-sensitive PI3K and its purported effector, the atypical protein kinase C (PKC)-z. Stimulation of PKC-z was prevented by the generic PKC inhibitor GF109203x (bisindolylmaleimide, 10 μM). Downregulation of diacylglycerol-sensitive (conventional and novel) PKCs by 24-h pretreatment with 1 μM phorbol 12-myristate 13acetate had no effect on IGF-I-stimulated Na1-K1-pump activity. Similarly, inhibition of only conventional and novel PKCs with GF109203x (1 μM) had no effect on IGF-Istimulated Na1-K1-pump activity. In contrast, a concentration of GF109203x (10 μM) that also inhibits the atypical PKCs abolished Na1-K1-pump stimulation by IGF-I. Neither the Na1-K1-2Cl2 cotransporter inhibitor bumetanide (100 μM) nor the Na1/H1 exchanger inhibitor HOE-694 (5 μM) affected the Na1-K1-pump stimulation by IGF-I, suggesting that a rise in intracellular Na1 concentration is not necessary for increased Na1-K1-pump activity. These results suggest that IGF-I directly stimulates the Na1-K1 pump via a signaling pathway involving PI3K and atypical PKC (z).