Oxidized-Ldl Enhances Coronary Vasoconstriction by Increasing the Activity of α and ε Protein Kinase C Isoforms
Oxidized low density lipoprotein (ox-LDL) plays a critical role in the development of atherosclerotic coronary vasospasm; however, the cellular mechanisms involved are not fully understood. We tested the hypothesis that ox-LDL enhances coronary vasoconstriction by increasing the activity of specific protein kinase C (PKC) isoforms in coronary smooth muscle. Active stress was measured in de-endothelialized porcine coronary artery strips, [Ca2+]i was monitored in single coronary smooth muscle cells loaded with fura-2, and the whole tissue, cytosolic and particulate fractions were examined for PKC activity and reactivity with isoform-specific anti-PKC antibodies using Western blot analysis. Ox-LDL (100 μg/ml) caused a slow but significant increase in active stress to 1.2±0.2 x103N/m2, that was completely inhibited by the PKC inhibitors staurosporine and calphostin C, with no significant increase in [Ca2+]i. Ox-LDL enhanced coronary contraction to increasing concentrations of 5-hydroxytryptamine (5-HT) and extracellular KCl with no additional increases in [Ca2+]i. Direct activation of PKC by phorbol 12,13-dibutyrate (PDBu, 0.1 μM) caused a contraction similar in magnitude and time course to ox-LDL induced contraction. PDBu also enhanced 5-HT and KCl-induced contraction with no additional increases in [Ca2+]i. Both ox-LDL and PDBu caused an increase in PKC activity in the particulate fraction and a decrease in the cytosolic fraction and increased the particulate/cytosolic PKC activity ratio. Western blot analysis revealed α-, δ-, ε- and ζ-PKC isoforms. In unstimulated tissue, α- and ε-PKC were mainly cytosolic, δ-PKC was mainly in the particulate fraction, while ζ-PKC was equally distributed in the cytosolic and particulate fractions. Ox-LDL and PDBu caused translocation of α- and ε-PKC from the cytosolic to particulate fraction, with minimal effect on the distribution of δ-PKC and ζ-PKC. Native LDL did not significantly affect coronary contraction, [Ca2+]i or PKC activity. These results suggest that ox-LDL enhances coronary vasoconstriction via activation and translocation of α- and ε-PKC isoforms in coronary smooth muscle.