Evidence for increased myofilament Ca2+ sensitivity in norepinephrine-activated vascular smooth muscle.
The agonist-induced change in Ca2+ sensitivity of smooth muscle myofilaments was investigated in intact and permeabilized vascular preparations isolated from the rat and the rabbit. In intact rat mesenteric artery, membrane depolarization by 80 mM K+ solution or alpha-adrenergic stimulation by norepinephrine (NE) increased tension monotonically with increasing extracellular Ca2+ concentration ([Ca2+]e). The [Ca2+]e-tension curve generated during activation by NE was located to the left of that during activation by high K+. The protein kinase C (PKC) activator 12-O-tetradecanoylphorbol-13-acetate (TPA) shifted the high K+ [Ca2+]e-tension curve to the left but did not affect the NE curve. In rat mesenteric artery permeabilized by alpha-toxin, tension was measured while the intracellular free Ca2+ concentration ([Ca2+]i) was controlled using 2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N'N'-tetraacetic acid and Ca2+ buffer solutions. The alpha-toxin-permeabilized fibers developed tension as a function of Ca2+ concentration. TPA and guanosine 5'-[gamma-thio]triphosphate (GTP gamma S, a nonhydrolyzable GTP analogue) significantly shifted the pCa-tension curve to the left. In intact rabbit inferior vena cava, tension was recorded simultaneously with [Ca2+]i as measured by fura-2. TPA caused a gradual increase in tension without change in [Ca2+]i. In rabbit mesenteric artery permeabilized by alpha-toxin, the tissue still responded to NE, indicating that alpha-adrenergic receptors remained intact. The response to NE was augmented by GTP and inhibited by guanosine 5'-[beta-thio]diphosphate (GDP beta S, a nonhydrolyzable GDP analogue) suggesting that a G protein is coupled with the alpha-adrenergic receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
Nishimura
J
J
Department of Pharmacology, University of Miami School of Medicine, Florida 33101.
Khalil
R A
RA
Drenth
J P
JP
van Breemen
C
C
D008841:Actin Cytoskeleton / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003599:Cytoskeleton / Q000187:drug effects*; D004533:Egtazic Acid; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D011921:Rats, Inbred WKY; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D010738:Type C Phospholipases / Q000494:pharmacology
D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D006160:Guanosine Triphosphate; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D009638:Norepinephrine