Failure of Bay K 8644 to induce RhoA kinase-dependent calcium sensitization in rabbit blood vessels.
OBJECTIVE
RhoA kinase (ROCK) participates in K(+) depolarization (KCl)-induced Ca(2+) sensitization of contraction. Whether constitutive, depolarization- or Ca(2+)-activated ROCK plays the major role in this signalling system remains to be determined. Here, we determined whether Bay K 8644, a dihydropyridine that promotes Ca(2+) channel clusters to operate in a persistent Ca(2+) influx mode, could cause ROCK-dependent Ca(2+) sensitization.


METHODS
Renal and femoral artery rings from New Zealand white rabbits were contracted with Bay K 8644. Tissues were frozen and processed to measure active RhoA and ROCK substrate (myosin phosphatase targeting subunit, MYPT1) and myosin light chain (MLC) phosphorylation, or loaded with fura-2 to measure intracellular free Ca(2+) ([Ca(2+)](i)). Effects of selective inhibitors of contraction were assessed in resting (basal) tissues and those contracted with Bay K 8644.


RESULTS
Bay K 8644 produced strong increases in [Ca(2+)](i), MLC phosphorylation and tension, but not in MYPT1 phosphorylation. ROCK inhibition by H-1152 abolished basal MYPT1-pT853, diminished basal MLC phosphorylation and inhibited Bay K 8644-induced increases in MLC phosphorylation and tension. MLC kinase inhibition by wortmannin abolished Bay K 8644-induced contraction and increase in MLC phosphorylation but did not inhibit basal MYPT1-pT853. H-1152 and wortmannin had no effect on MYPT1-pT696, but 1 microM staurosporine inhibited basal MYPT1-pT853, MYPT1-pT696 and MLC phosphorylation.


CONCLUSIONS
These data suggest that the constitutive activities of ROCK and a staurosporine-sensitive kinase regulate basal phosphorylation of MYPT1, which participates along with activation of MLC kinase in determining the strength of contraction induced by the Ca(2+) agonist, Bay K 8644.
Alvarez
S M
SM
Departments of Biochemistry and Molecular Biology and Pediatrics, Virginia Commonwealth University, School of Medicine, Richmond, VA, USA.
Miner
A S
AS
Browne
B M
BM
Ratz
P H
PH
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005263:Femoral Artery / Q000187:drug effects / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D018994:Myosin Light Chains / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011817:Rabbits; D012077:Renal Artery / Q000187:drug effects / Q000378:metabolism; D054460:rho-Associated Kinases / Q000378:metabolism*
D018994:Myosin Light Chains; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D054460:rho-Associated Kinases; D009219:Myosin-Light-Chain Kinase; D043263:Myosin-Light-Chain Phosphatase; D002118:Calcium