SMOOTH-MUSCLE CELL EXPRESSION OF TYPE-I CYCLIC GMP-DEPENDENT PROTEIN-KINASE IS SUPPRESSED BY CONTINUOUS EXPOSURE TO NITROVASODILATORS, THEOPHYLLINE, CYCLIC-GMP, AND CYCLIC-AMP

A key component of the nitric oxide-cyclic guanosine monophosphate (cG MP) pathway in smooth muscle cells (SMC) is the type I GMP-dependent p rotein kinase (PK-G I), Activation of PK-G I mediates the reduction of cytoplasmic calcium concentrations and vasorelaxation, In this manusc ript, we demonstrate that continuous exposure of SMC in culture to the nitrovasodilators S-nitroso-N-acetylpenicillamine (SNAP) or sodium ni troprusside (SNP) results in similar to 75% suppression of PK-G I mRNA by 48 h. PK-G I mRNA and protein were also suppressed by continuous e xposure to cGMP analogues 8-bromo- and 8-(4-chlorophenylthio) guanosin e-3,5-monophosphate or the cAMP analogue dibutyryl cAMP, These results suggest that activation of one or both of the cyclic nucleotide-depen dent protein kinases mediates PK-G I mRNA suppression, Using isoform-s pecific cDNA probes, only the PK-G I alpha was detected in SMC, either at baseline or after suppression, while PK-G I beta was not detected, indicating that isoform switch was not contributing to the gene regul ation. Using the transcription inhibitor actinomycin D, the PK-G I mRN A half-life in bovine SMC was observed to be 5 h, The half-life was no t affected by the addition of SNAP to actinomycin D, indicating no eff ect on PK-G I mRNA stability, Nuclear runoff studies indicated a suppr ession of PK-G I gene transcription by SNAP. PK-G I suppression was al so observed in vivo in rats given isosorbide dinitrate in the drinking water, with a dose-dependent suppression of PK-G I protein in the aor ta. PK-G I antigen in whole rat lung extract was also suppressed by ad ministration of isosorbide or theophylline in the drinking water, Thes e data may contribute to our understanding of nitrovasodilator resista nce, a phenomenon resulting from continuous exposure to nitroglycerin or other nitrovasodilators.