Premium
Mechanisms of tolerance to sodium nitroprusside in rat cultured aortic smooth muscle cells
Author(s) -
Papapetropoulos Andreas,
Go Carolyn Y.,
Murad Ferid,
Catravas John D.
Publication year - 1996
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1996.tb15167.x
Subject(s) - zaprinast , sodium nitroprusside , downregulation and upregulation , western blot , endocrinology , snap , phosphodiesterase inhibitor , medicine , chemistry , soluble guanylyl cyclase , phosphodiesterase , biology , nitric oxide , biochemistry , enzyme , guanylate cyclase , computer graphics (images) , computer science , gene
1 While exposure of smooth muscle cells to sodium nitroprusside (SNP) leads to the development of tolerance to soluble guanylate cyclase (sGC) activation, the mechanisms responsible for this phenomenon in intact cells remain unclear. In the present study, possible mechanisms of tolerance were investigated in a cell culture model where sGC activity was estimated from the accumulation of cyclic GMP in response to 10 μ m SNP over a 15 min period in the presence of a phosphodiesterase (PDE) inhibitor. 2 Pretreatment of rat aortic smooth muscle cells with 10–500 μ m SNP led to a dose‐dependent downregulation of cyclic GMP accumulation upon subsequent SNP stimulation. This effect was evident as early as 2 h following incubation with 10 μ m SNP, reached a plateau at 4 h and was blocked by coincubation with 30 μ m oxyhaemoglobin. 3 Pretreatment of smooth muscle cells with the PDE inhibitor, zaprinast, resulted in downregulation of the SNP‐induced cyclic GMP accumulation in a time‐ and concentration‐dependent manner, that was first evident after 12 h. Moreover, while the zaprinast‐induced downregulation of cyclic GMP accumulation was completely inhibited by the protein kinase A (PKA) inhibitor, H89, tolerance to SNP was partially reversed by H89. 4 β 1 sGC steady state mRNA levels of S‐nitroso N‐acetylpenicillamine (SNAP)‐ or 8Br‐cyclic GMP‐pretreated cells were unchanged, as indicated by Northern blot analysis. However, Western blot analysis revealed that α 1 protein levels were decreased in zaprinast, but not in SNP, SNAP or 8Br‐cyclic GMP pretreated cells. 5 While thiol depletion did not prevent the development of tolerance, pretreatment of cells with SNP in the presence of reducing agents partially or completely restored the ability of cells to respond to SNP. 6 We conclude that tolerance to SNP results from two distinct mechanisms: an early onset, NO‐mediated event that is reversed by reducing agents and a more delayed, PKA‐sensitive process that is mediated through increases in cyclic GMP and a decrease in sGC protein levels.