Intracellular Ca2+ elevation and contraction due to prostaglandin F2alpha in rat aorta

Prostaglandin F2alpha was tested to determine (a) whether its effect on intracellular Ca2+ levels ([Ca2+]i) and force in vascular smooth muscle was mediated through activation of the thromboxane A2 and/or prostaglandin receptor, and (b) the relative roles of Ca2+ influx via L-type and non-L-type Ca2+ channels in prostaglandin receptor-mediated contraction. [Ca2+]i and force were measured simultaneously in fura-2-loaded rat aortic strips. The thromboxane A2 receptor antagonist, SQ29548 ([1S]-1a,2b(5Z),3b,4a-7-(3-[2-[(phenylamino)carbonyl] hydrazinomethyl)-7-oxobicyclo-[2.2.1]hept-2-yl-5-heptenoic acid), prevented the prostaglandin F2alpha-induced plateau [Ca2+]i elevation and force by 80-90%, while abolishing these responses due to the thromboxane A2 receptor agonist, U46619 (9,11-dideoxy-9alpha,11alpha-methanoepoxy prostaglandin F2alpha). Prostaglandin F2alpha (+ SQ29548)-induced plateau [Ca2+]i elevation and force were not inhibited by verapamil. Ni2+, a non-selective cation channel blocker, in the presence of verapamil, abolished the prostaglandin F2alpha (+ SQ29548)-elevated [Ca2+]i, while the contraction was only partially inhibited. These results suggest that, in rat aorta, (1) elevated [Ca2+]i and force due to high prostaglandin F2alpha concentrations largely results from thromboxane A2 receptor activation, and (2) the prostaglandin component of the prostaglandin F2alpha-induced contraction is dependent on Ca2+ influx via non-L-type channels.