Mechanisms of cGMP-dependent mesangial-cell relaxation: a role for myosin light-chain phosphatase activation.
Although the cGMP-dependent relaxation of contractile cells seems to depend on the ability of the cyclic nucleotide to interfere with intracellular calcium, this does not appear to be the only mechanism involved. The present experiments were designed to analyse alternative mechanisms, trying to test the hypothesis that cGMP could relax rat mesangial cells by activating myosin light-chain phosphatase (MLC-PP), with the subsequent dephosphorylation of myosin light chain (MLC). The effect of a cGMP analogue, dibutyryl cGMP (dbcGMP), on angiotensin II-(AII) and PMA-induced MLC phosphorylation (MLCP) was tested, in the presence of calyculin A (CA), an inhibitor of MLC-PP. MLCP was measured, after cell labelling with (32)P, by immunoprecipitation. dbcGMP prevented the increased MLCP induced by AII or PMA, and this inhibition was blocked by CA. dbcGMP also increased the MLC dephosphorylation observed in cells incubated with AII and in which MLC kinase and protein kinase C activities were blocked. The AII-elicited increased intracellular calcium concentration was only partially inhibited by dbcGMP. These results suggest that the cGMP-induced mesangial-cell relaxation could be due, at least partially, to the stimulation of MLC-PP.
Torrecillas
G
G
Department of Physiology, Universidad de Alcalá, Carretera de Madrid-Barcelona km 33.6, 28871 Alcalá de Henares, Madrid, Spain.
Díez-Marqués
M L
ML
García-Escribano
C
C
Bosch
R J
RJ
Rodríguez-Puyol
D
D
Rodríguez-Puyol
M
M
D000804:Angiotensin II / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D003995:Dibutyryl Cyclic GMP / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology*; D008387:Marine Toxins; D018994:Myosin Light Chains / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D019311:Staurosporine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors / Q000494:pharmacology
D001381:Azepines; D008387:Marine Toxins; D018994:Myosin Light Chains; D010080:Oxazoles; C056218:ML 9; D000804:Angiotensin II; D003995:Dibutyryl Cyclic GMP; C059041:calyculin A; D011493:Protein Kinase C; D009219:Myosin-Light-Chain Kinase; D010749:Phosphoprotein Phosphatases; D043263:Myosin-Light-Chain Phosphatase; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium