Calcium-independent activation of contractile apparatus in smooth muscle by calyculin-A.
Calyculin-A (CL-A), a novel marine toxin isolated from Discodermia calyx, caused contraction in the smooth muscle of guinea pig taenia ceci and rat aorta in the presence or absence (with 1 mM ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid) of external Ca++ at concentrations ranging from 1 X 10(-8) to 1 X 10(-6) M. In the presence of external Ca++, the contraction induced by CL-A was accompanied by an increase in the cytosolic free Ca++ concentration [( Ca++]cyt) as measured by the fluorescence indicator fura-2. Verapamil (3 X 10(-6) M) inhibited the increase in [Ca++]cyt, but not tension development caused by CL-A. In the absence of external Ca++, CL-A still caused contraction without changing [Ca++]cyt. Thus, from studies with intact smooth muscle it was demonstrated that, in the absence of external Ca++, CL-A can induce a contraction that was not accompanied by an increase in [Ca++]cyt. In permeabilized taenia, CL-A caused contraction in the absence of Ca++ (with 2 mM ethylene glycol bis(beta-aminoethyl ether)N,N'-tetraacetic acid) at concentrations similar to those required to contract intact tissue. This contraction was inhibited by the nonselective kinase inhibitors such as amiloride (1 X 10(-3) M) and K-252a (2 X 10(-5) M). Low concentrations of Ca++ (approximately 1 X 10(-6) M) augmented the CL-A-induced contraction in the permeabilized taenia. In native actomyosin prepared from chicken gizzard CL-A induced phosphorylation of the 20 kDa myosin light chain (MLC) in the absence of Ca++.(ABSTRACT TRUNCATED AT 250 WORDS)
Ishihara
H
H
Department of Veterinary Pharmacology, Faculty of Agriculture, University of Tokyo, Japan.
Ozaki
H
H
Sato
K
K
Hori
M
M
Karaki
H
H
Watabe
S
S
Kato
Y
Y
Fusetani
N
N
Hashimoto
K
K
Uemura
D
D
D015087:2',3'-Cyclic-Nucleotide Phosphodiesterases / Q000378:metabolism; D000205:Actomyosin / Q000378:metabolism; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002432:Cecum / Q000187:drug effects / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008387:Marine Toxins; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D010080:Oxazoles / Q000494:pharmacology*; D010766:Phosphorylation; D011161:Porifera; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology
D008387:Marine Toxins; D010080:Oxazoles; D004533:Egtazic Acid; C059041:calyculin A; D000205:Actomyosin; D014700:Verapamil; D009219:Myosin-Light-Chain Kinase; D015087:2',3'-Cyclic-Nucleotide Phosphodiesterases; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium