Fig. 6.

Extracellular PP_i accumulation in VSMC cultures is modulated by time postplating. A: extracellular levels of PP_i (top, linear scale) and ATP (bottom, log scale) following transfer of cultured VSMC to basal saline assay medium in the absence (▪, control) and presence (□) of 300 μM MeATP. Data points represent means ± SE from the triplicates of a representative experiment repeated three times using passage 2 VSMC at 3 days postplating (dpp). B: VSMC from the same preparation as in A, but cultured 6 additional days before the analysis of PP_i and ATP accumulation. Data points represent means ± SE from the triplicates of a representative experiment repeated three times. C: VSMC from the same preparation as in A and assayed for PP_i and ATP levels following transfer of basal saline assay medium alone (▪, control; −ATP) or assay medium supplemented with 500 nM exogenous ATP (□) or with 500 nM ATP plus 300 μM MeATP (•). Data represent means ± SE from the triplicates of a representative experiment repeated three times. D: statistical analysis of net PP_i generation (ΔPP_i) by VSMC as a function of passage number and days postplating. Data points represent means ± SE from 3 separate experiments (each performed in triplicate) with different VSMC preparations. *P < 0.05, two-way ANOVA with the Bonferroni post hoc test. ΔPP_i = [PP_i]_{120 min} − [PP_i]_{3 min}.