cSrc is a major cytosolic tyrosine kinase in vascular tissue

We are interested in identifying, in vascular tissue, nonreceptor tyrosine kinases that may be responsible for the contractile actions of G-protein-co upled agonists such as angiotensin II. By using a series of chromatographic steps, including ion exchange, hydrophobic, and affinity chromatography, w e have isolated a major fraction of tyrosine kinase activity from the cytos olic fraction of porcine aorta tissue. According to (i) its immunologic cro ss-reactivity with the monoclonal anti-cSrc antibody, m327, and with the N- terminally directed monoclonal cSrc2-17 antibody, (ii) its inhibition by th e C-terminal cSrc kinase, CSK, and (iii) its specificity for phosphorylatin g tyrosine 15 in the cdc2(6-20) peptide kinase substrate, we conclude that the kinase we have isolated represents porcine cSrc. A substantial proporti on of the enzyme (>70%) was recovered in the cytoplasmic fraction from aort a tissue. The profile of inhibition of the human and porcine cSrc enzymes b y a spectrum of tyrosine kinase inhibitors (PP1 much greater than AG82 > AG 490 congruent to genistein > AG10) was compared with the profile of inhibit ion of angiotensin II mediated contraction in a porcine coronary vascular p reparation (AGIO much greater than genistein greater than or equal to AG82 greater than or equal to AG490; PPI inactive). The different inhibitory pro files indicated that cSrc does not represent the vascular tyrosine kinase r esponsible for the contractile actions of angiotensin II. We suggest, nonet heless, that cSrc plays a key role for other actions of angiotensin II in i ntact vascular tissue, such as the regulation of mitogen-activated protein kinase activity and gene transcription.