ANGIOTENSIN-II RESPONSES OF VASCULAR SMOOTH-MUSCLE CELLS FROM HYPERTENSIVE RATS - ENHANCEMENT AT THE LEVEL OF P42 AND P44 MITOGEN-ACTIVATEDPROTEIN-KINASE

1 Stimulation of the AT1 receptor by angiotensin II (AII) gives a larg er mitogenic response in vascular smooth muscle cells from spontaneous ly hypertensive rats (SHR) compared to those from normotensive (WKY) c ontrols. Here we investigated whether the p42 and p44 mitogen activate d protein kinase (MAPK) pathway is differentially regulated in these c ells by AT(1) receptors. 2 We showed that there is a similar level of p42 and p44 MAPK immunoreactivity in the SHR and WKY derived cells. 3 However, by use of an antiserum specific for the tyrosine phosphorylat ed form of MAPK, and an assay with a nonapeptide MAPK substrate, we sh owed that AII (100 nM)-stimulated phosphorylation and activation of p4 2(mapk) and p44(mapk) are enhanced in the SHR derived cells. 4 This in creased MAPK activity in SHR derived cells was also seen on protein ki nase C activation with 100 nM phorbol myristate acetate (PMA). The siz e and time course of the response to PMA was the same as that to AII i n each cell type. 5 The protein kinase C inhibitor Ro 31-8220 attenuat ed the early (2 min) phase of AII stimulation of MAPK activity and the entire stimulation caused by PMA. At longer times of AII stimulation both p42(mapk) and p44(mapk) were activated by an Ro 31-8220-insensiti ve mechanism. 6 Agonist or PMA stimulation of MAPK activity was inhibi ted by the tyrosine kinase inhibitor genistein. AII stimulated tyrosin e protein phosphorylation to a greater degree in SHR than WKY cells. 7 These results show that the MAPK response of SHR derived cells is inc reased over that of WKY cells by mechanisms independent of the enhance d stimulation of phospholipase C; amplification at the level of sequen tial protein kinase C and tyrosine kinase steps leads to the enhanced responsiveness of MAPK in the SHR derived cells.