Phosphatidylinositol 3-kinase modulates vascular smooth muscle contraction by calcium and myosin light chain phosphorylation-independent and -dependent pathways.
Regulation of smooth muscle contraction involves a number of signaling mechanisms that include both kinase and phosphatase reactions. The goal of the present study was to determine the role of one such kinase, phosphatidylinositol (PI)3-kinase, in vascular smooth muscle excitation-contraction coupling. Using intact medial strips of the swine carotid artery, we found that inhibition of PI3-kinase by LY-294002 resulted in a concentration-dependent decrease in the contractile response to both agonist stimulation and membrane depolarization-dependent contractions and a decrease in Ca(2+)-dependent myosin light chain (MLC) phosphorylation, the primary step in the initiation of smooth muscle contraction. Inhibition of PI3-kinase also depressed phorbol dibutyrate-induced contractions, which are not dependent on either Ca(2+) or MLC phosphorylation but are dependent on protein kinase C. To determine the Ca(2+)-dependent site of action of PI3-kinase, we determined the effect of several inhibitors of calcium metabolism on LY-294002-dependent inhibition of contraction. These inhibitors included nifedipine, SK&F-96365, and caffeine. Only SK&F-96365 blocked the LY-294002-dependent inhibition of contraction. Interestingly, all compounds blocked the LY-294002-dependent inhibition of MLC phosphorylation. Our results suggest that activation of PI3-kinase is involved in a Ca(2+)- and MLC phosphorylation-independent pathway for contraction likely to involve protein kinase C. In addition, our results also suggest that activation of PI3-kinase is involved in Ca(2+)-dependent signaling at the level of receptor-operated calcium channels.
Su
Xiaoling
X
Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
Smolock
Elaine M
EM
Marcel
Kristi N
KN
Moreland
Robert S
RS
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002339:Carotid Arteries / Q000502:physiology*; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D009025:Morpholines / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011189:Potassium Chloride / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D013552:Swine
D002110:Caffeine; D002118:Calcium; D002867:Chromones; D004791:Enzyme Inhibitors; D006632:Histamine; D009025:Morpholines; D018994:Myosin Light Chains; D009219:Myosin-Light-Chain Kinase; D009543:Nifedipine; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011189:Potassium Chloride; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one