Evidence for the presence of endothelin ET A receptors in endothelial cells in situ on the aortic side of porcine aortic valve

1 In the present study, we determined whether ET A receptors are present on endothelial cells in situ , by use of front‐surface fluorometry of fura‐2‐loaded porcine aortic valvular strips and reverse transcription polymerase chain reaction (RT‐PCR). 2 Although endothelin‐1 (ET‐1) and endothelin‐3 (ET‐3) induced maximum elevations of cytosolic Ca 2+ concentrations ([Ca 2+ ] i ) at 10 −7 m , the peak elevations of [Ca 2+ ] i induced by ET‐1 were much greater than those induced by ET‐3. 3 The application of ET‐1 after ET‐3 induced an additional increase in [Ca 2+ ] i , while the application of ET‐3 after ET‐1 had no effect. A selective ET A receptor antagonist, BQ‐123, partially inhibited the ET‐1‐induced Ca 2+ transient but had no effect on ET‐3‐induced Ca 2+ transients. These experiments indicated the presence of functioning ET A receptors in addition to ET B receptors in endothelial cells in situ.4 The sequence of pig lung ET A receptor complimentary DNA (cDNA) was determined by PCR. RT‐PCR, using specific primers for pig ET A receptor sequence and total RNA from endothelial cells on the aortic side of the aortic valve, gave the expected size of band. This PCR product was sequenced and was found to be identical to the sequence of the pig lung ET A receptor. 5 The partial sequence of the pig lung ET B receptor was also determined. RT‐PCR for the pig ET B receptor revealed that endothelial cells of the aortic valve express ET B receptor messenger RNA (mRNA). 6 We confirmed that functioning ET A receptors and expression of ET A receptor mRNA exist in the endothelial cells on the aortic side of porcine aortic valves.