Low concentrations of sphingosylphosphorylcholine enhance pulmonary artery vasoreactivity -: The role of protein kinase Cδ and Ca2+ entry

Sphingosylphosphorylcholine ( SPC) is a powerful vasoconstrictor, but in vitro its EC50 is approximate to 100-fold more than plasma concentrations. We examined whether subcontractile concentrations of SPC (<= 1 mu mol/ L) modulated vasoreactivity of rat intrapulmonary arteries using myography and measurement of intracellular [ Ca2+]. SPC ( 1 mu mol/ L) had no effect on force or intracellular [Ca2+] on its own, but dramatically potentiated constrictions induced by approximate to 25 mmol/ L [K+], such that at 40 minutes, force and intracellular [Ca2+] ( Fura PE3 340/ 380 ratio) were increased by 429 +/- 96% and 134 +/- 26%, respectively. The potentiation was stereospecific, apparent at concentrations > 100 nmol/ L of SPC, and independent of the endothelium, 2-aminoethoxydiphenylborane-sensitive Ca2+ entry, and Rho kinase. It was abolished by the phospholipase C inhibitor U73122, the broad spectrum protein kinase C ( PKC) inhibitor Ro31-8220, and the PKC delta inhibitor rottlerin, but not by Go6976, which is ineffective against PKC delta. The potentiation could be attributed to enhancement of Ca2+ entry. SPC also potentiated the responses to prostaglandin F-2 alpha and U436619, which activate a 2-aminoethoxydiphenylborane sensitive nonselective cation channel in intrapulmonary arteries. In this case, potentiation was partially inhibited by diltiazem but abolished by 2-aminoethoxydiphenylborane, Ro31- 8220, and rottlerin. SPC ( 1 mu mol/ L) caused translocation of PKC delta to the perinuclear region and cytoskeleton of cultured intrapulmonary artery smooth muscle cells. We present the novel finding that low, subcontractile concentrations of SPC potentiate Ca2+ entry in intrapulmonary arteries through both voltage-dependent and independent pathways via a receptor-dependent mechanism involving PKC delta. This has implications for the physiological role of SPC, especially in cardiovascular disease, where SPC is reported to be elevated.