Effects of prostaglandins E1 and E2 on cultured smooth muscle cells and strips of rat aorta.

Using patch-clamp and Indo-1AM techniques, we studied the effects of prostaglandins (PG) E1 and E2 on transmembrane ionic currents and cytosolic calcium concentration ([Ca2+]i) in cultured rat aortic smooth muscle cells (SMC) and on isotonic contraction-relaxation of strips of the rat thoracic aorta. In voltage-clamped at -70 mV single SMC PGE1 and PGE2 in concentration 100 nM evoked inward and outward currents. The inward current was unaffected by the Cl channel blocker DIDS (0.1 mM). The outward current was blocked by internal Cs+ and external Ba2+ and was likely due to increased Ca2+ activated K+ conductance. Application of PGE1 and PGE2 in the bath solution evoked relaxation of aortic strips in a concentration-dependent manner. In both cases indomethacin was ineffective. The rise in [Ca2]i evoked by PGEs was observed in single cells loaded with Indo-1AM. Whole-cell voltage-activated T- and L-type Ca2+ currents were reduced by both PGE1 and PGE2. The results obtained in this work indicate that in cultured rat aortic SMC PGE1 and PGE2 increase [Ca2+]i with subsequent activation of Ca(2+)-dependent K+ currents, block voltage-activated Ca2+ currents, and at the same time induce relaxation of aortic strips.