RT Journal Article
SR Electronic
T1 Stimulated Tyrosine Phosphorylation of Phosphatidylinositol 3-Kinase Causes Acidic pH-Induced Contraction in Spontaneously Hypertensive Rat Aorta
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 1255
OP 1264
DO 10.1124/jpet.102.041475
VO 303
IS 3
A1 Dileep Kumar Rohra
A1 Tohru Yamakuni
A1 Ken-Ichi Furukawa
A1 Noe Ishii
A1 Takashi Shinkawa
A1 Toshiaki Isobe
A1 Yasushi Ohizumi
YR 2002
UL http://jpet.aspetjournals.org/content/303/3/1255.abstract
AB Acidic pH induced a contraction (APIC) in isolated aortas from spontaneously hypertensive (SHR) and Wistar Kyoto rats, but failed to produce any response in age-matched Wistar rat aorta. This study was conducted to test the hypothesis that tyrosine phosphorylation of proteins is a molecular mechanism underlying the APIC. Tyrosine kinase inhibitors, genistein and tyrphostin 23 inhibited the APIC in a concentration-dependent manner. APIC was inhibited by phosphatidylinositol 3-kinase (PI3-kinase) inhibitors, LY-294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride] and wortmannin. Consistent with the results from tension measurement experiments, Western blot analysis showed that acidic pH induced an appreciable increment of tyrosine phosphorylation of 85-kDa protein (p85) in SHR aorta, which was completely inhibited by tyrphostin 23, whereas in Wistar rat aorta, the protein tyrosine phosphorylation was not observed. Further investigations using immunoprecipitation followed by Western blotting confirmed an increase in the tyrosine phosphorylation of p85. Analysis by SDS-polyacrylamide gel electrophoresis followed by silver staining of the gel revealed that amounts of multiple proteins with molecular sizes of 120, 130, 210, and 225 kDa were increased at acidic pH, which were immunoprecipitated with anti-phosphotyrosine antibody. Western blotting using a specific anti-PI3-kinase antibody identified the p85 as the regulatory subunit of PI3-kinase, whereas 120-, 130-, and 225-kDa proteins were identified by mass spectrometry as pro-α2 (I) collagen, collagen α1 (I) chain, and fibernectin I, respectively. As assayed by Western blotting using anti-myosin light chain (MLC) antibody, acidic pH induced a stimulation of MLC phosphorylation, and the stimulated MLC phosphorylation was abolished by tyrphostin 23 and LY-294002. These results suggest that acidic pH induces an increase in tyrosine phosphorylation of PI3-kinase, resulting in the MLC phosphorylation-dependent contraction of SHR aorta.