Lysophosphatidylcholine potentiates vascular contractile responses by enhancing vasoconstrictor-induced increase in cytosolic free Ca2+ in rat aorta

We investigated the effects of palmitoyl-L-alpha-lysophosphatidylcholine on the contractile responses of the endothelium-denuded rat aorta to high KC, noradrenaline, UK14,304 (5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline) ( a selective alpha(2) adrenoceptor agonist) and phorbol 12-myristate 13-acet ate (PMA). Lysophosphatidylcholine at concentrations from 10(-6) M to 10(-4 ) M did not contract aortic strips. However, lysophosphatidylcholine strong ly potentiated the UK14,304-induced contraction. High K+- and PMA-induced c ontractions were also potentiated. In contrast, the noradrenaline-induced c ontraction was only slightly potentiated by 10(-5) M lysophosphatidylcholin e. In fura PE-3-loaded aortic strips, lysophosphatidylcholine (10(-5) M) ma rkedly augmented the increase in both cytosolic free Ca2+ ([Ca2+](i)) and c ontractile tension induced by UK14,304, high K+ and PMA. Nicardipine (10(-7 ) M) and 10(-6) M Ro-31-8220 ({1-[3-(amidinothio)propyl-1H-indoyl-3-yl]-3-( 1-methyl-1H-indoyl-3-yl)-maleimide-methane sulfate) strongly inhibited the increase in [Ca2+](i) and contractile tension induced by UK14,304 and in th e presence of these inhibitors, the enhancing effects of lysophosphatidylch oline were attenuated. However, the enhancing effect on high K+-induced con traction was not affected by Ro-31-8220. These results suggest that lysopho sphatidylcholine may cause an augmentation of the increase in [Ca2+](i) ind uced by UK14,301 which response is depend on protein kinase C activation an d in this way potentiate contractile responses in the rat aorta. Protein ki nase C independent mechanisms may also be involved in the enhancing effect of lysophosphatidylcholine an smooth muscle contraction. (C) 1998 Elsevier Science B.V. All rights reserved.