DIFFERENTIAL EFFECT OF 3 COMMERCIAL HEPARINS ON NA+ H+ EXCHANGE AND GROWTH OF PASMC/

Heparin preparations vary in chemical content and in antiproliferative activity for pulmonary artery smooth muscle cells (PASMC). Intracellu lar alkalinization via stimulation of the Na+/H+ antiporter appears to be a permissive event for proliferation of PASMC. We wondered whether the variable effect of heparin preparations on PASMC growth might be due to different degrees of inhibition of the Na+/H+ antiporter and wh ether variations in chemical formulation might correlate with the inhi bition. Fluorescent microscopy of bovine PASMC was done using a dye wi th which fluorescence varies directly with intracellular pH (pH(i)). B ovine PASMC were preincubated with three heparin preparations previous ly shown to vary in antiproliferative activity at 1.0 mu g/ml for 24 h . Platelet-derived growth factor (PDGF; 60 ng/ml) on PASMC without hep arin resulted in a rise in pH(i) of 0.27 +/- 0.02 pH units. The rise i n pH units in heparin-treated PASMC was 0.34 +/- 0.03 with Choay, 0.21 +/- 0.02 with Elkins-Sinn, and 0.07 +/- 0.02 with Upjohn (+/- SE; all P < 0.05; n = 5). Upjohn heparin incubation for as little as 15 min s till impeded the rise in pH induced by PDGF. Heparin did not block the Na+/H+ exchanger directly, as it still restored pH(i) in response to an acid load. Compared with PASMC proliferation induced by 60 ng/ml PD GF, 1 mu g/ml of Choay, Elkins-Sinn, and Upjohn heparin produced -4 +/ - 7.4, 1.4 +/- 4.8, and 48 +/- 2.2% inhibition of PDGF control, respec tively (P < 0.05 for Upjohn compared with PDGF and Choay). The heparin s varied in protein content and amino acid composition. However, amino acid and glucosamine composition total sulfation, and extent of 3-O-s ulfation did not predict their activity. Thus inhibition of PDGF activ ation of the Na+/H+ antiporter by a given heparin preparation correlat ed well with its ability to inhibit PASMC proliferation.