NA-H+ EXCHANGE INHIBITORS DECREASE NEOINTIMAL FORMATION AFTER RAT CAROTID INJURY - EFFECTS ON SMOOTH-MUSCLE CELL-MIGRATION AND PROLIFERATION()

The presence of multiple growth stimuli at the sites of vascular injur y following angioplasty suggests that therapies targeted toward common growth pathways will be more effective than therapies that inhibit on ly a single growth factor. We tested this hypothesis using amiloride a nd ethyl isopropyl amiloride (EIPA), which are inhibitors of the Na+-H + exchanger, whose activity is required in many cells for proliferatio n and migration. In the rat carotid injury model, EIPA (100 mug/h for 15 days) significantly decreased intimal area and the ratio of intimal to medial area, whereas amiloride (25 mug/h) showed an inhibitory tre nd that was similar to that observed for captopril (80 mg/kg per day) and heparin (25 U/h). EIPA and amiloride inhibited rat vascular smooth muscle cell DNA synthesis, with IC50 values of 8.8 and 82.2 muM, resp ectively. Using platelet-derived growth factor as a chemoattractant, E IPA caused a concentration-dependent inhibition of migration (IC50, al most-equal-to 60 muM). Because amiloride and EIPA have nonspecific eff ects on cellular function (especially inhibition of tyrosine kinases), we sought to characterize the specific role of the Na+-H+ exchanger i n vascular smooth muscle cell proliferation and migration. We generate d a Na+-H+ exchanger-deficient mutant cell line [RNHE(-)]. Studies wit h these cells suggested that the inhibitory effects of EIPA and amilor ide were mediated only in part via Na+-H+ exchange because (1) RNHE(-) cells grew well at pH 6.8 to 7.5 in bicarbonate-containing medium, an d (2) there was no difference in migration in response to platelet-der ived growth factor in the RNHE(-) cells. In summary, these data indica te that amiloride and EIPA inhibit neointimal formation in the rat car otid after injury. However, the mechanism of inhibition is likely to i nvolve cellular events other than Na+-H+ exchange, such as an effect o n tyrosine kinases.