Impaired arachidonic acid-mediated activation of large-conductance Ca ²⁺-activated K⁺ channels in coronary arterial smooth muscle cells in Zucker Diabetic Fatty rats

We studied the arachidonic acid (AA)-mediated modulation of large-conductance Ca²⁺-activated K⁺ (BK) channels in coronary arterial smooth myocytes from lean control and Zucker Diabetic Fatty (ZDF) rats. A total of 1 μmol/l AA enhanced BK current by 274% in lean and by 98% in ZDF rats. After incubation with 10 μmol/l indomethacin, 1 μmol/l AA increased BK currents by 80% in lean and by 70% in ZDF rats. Vasoreactivity studies showed that the dilation of small coronary arteries produced by 1 μmol/l AA was reduced by 44% in ZDF rats. [³H]6-keto-prostagladin F_1α ([³H]6-keto-PGF_1α,), the stable metabolite of prostacyclin (PGI₂), was the major [³H]AA metabolite produced by coronary arteries of lean vessels, but ZDF vessels produced only 15% as much [³H]6-keto-PGF_1α. BK channel activation and vasorelaxation by iloprost were similar in lean and ZDF rats. Immunoblots showed a 73% reduction in PGI₂ synthase (PGIS) expression in ZDF vessels compared with lean vessels, and there was no change in cyclooxygenase (COX) and BK channel expressions. Real-time PCR studies showed that mRNA levels of PGIS, COX-1, and COX-2 were similar between lean and ZDF vessels. We conclude that PGI₂ is the major AA metabolite in lean coronaries, and AA-mediated BK channel activation is impaired in ZDF coronaries due to reduced PGIS activity.