Selective sequestration of nitric oxide by subcellular components of vascular smooth muscle and platelets: relationship to nitric oxide stimulation of the soluble guanylyl cyclase.

Sequestration of nitric oxide (NO) by subcellular fractions isolated from bovine pulmonary arterial medial layer (BPA) and rabbit platelets (RP) was studied utilizing a novel chemiluminescence--headspace gas technique. Sequestration in all fractions was similarly rapid (5 min) and remained constant for at least 30 min. When incubated with 108 pmol of NO, the BPA mitochondrial, microsomal, and nuclear fractions sequestered 22.8 +/- 1.9, 20.5 +/- 2.2 and 15.2 +/- 3.6% of the NO, respectively (n = 14). However, significantly more of the 108 pmol of NO, 36.8 +/- 2.8 and 32.9 +/- 3.6%, respectively, was sequestered by the BPA homogenate (about 2 mg protein/mL) and BPA cytosolic fraction (about 1 mg protein/mL) (n = 19). Also, RP cytosolic fraction (about 3 mg protein/mL) sequestered a greater amount of NO than any BPA fraction when incubated with 108 pmol of NO (83.0 +/- 1.0%; n = 3). Analysis of the binding data obtained for the BPA homogenate and cytosolic fraction was consistent with the existence of two binding sites, one site with a Kd of approximately 100 nM and another with a Kd of approximately 1 microM. Both the BPA homogenate fraction and the cytosolic fraction as well as the RP cytosolic fraction were shown to have soluble guanylyl cyclase activity. The nitrovasodilator sodium nitroprusside (SNP) caused a concentration-dependent increase in the activity of this enzyme in all these fractions. Maximum stimulations caused by 1 mM SNP in BPA homogenate fraction, BPA cytosolic fraction, and RP cytosolic fraction were equivalent to 2-, 4- and 3-fold increases in catalytic activity, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)