ABSTRACT
Dendroaspis natriuretic peptide (DNP), a newly-described natriuretic peptide, relaxes gastrointestinal smooth muscle. L-type calcium channel currents play an important role in regulating smooth muscle contraction. The effect of DNP on L-type calcium channel currents in gastrointestinal tract is still unclear. This study was designed to investigate the effect of DNP on barium current (I(Ba)) through the L-type calcium channel in gastric antral myocytes of guinea pigs and cGMP-pathway mechanism. The whole-cell patch-clamp technique was used to record L-type calcium channel currents. The content of cGMP in guinea pig gastric antral smooth muscle and perfusion solution was measured using radioimmunoassay. DNP markedly enhanced cGMP levels in gastric antral smooth muscle tissue and in perfusion medium. DNP concentration-dependently inhibited I(Ba) in freshly isolated guinea pig gastric antral circular smooth muscle cells (SMCs) of guinea pigs. DNP-induced inhibition of I(Ba) was partially blocked by LY83583, an inhibitor of guanylate cyclase. KT5823, a cGMP-dependent protein kinase (PKG) inhibitor, almost completely blocked DNP-induced inhibition of I(Ba). However, DNP-induced inhibition of I(Ba) was potentiated by zaprinast, an inhibitor of cGMP-sensitive phosphodiesterase. Taken together, DNP inhibits L-type calcium channel currents via pGC-cGMP-PKG-dependent signal pathway in gastric antral myocytes of guinea pigs.
Subject(s)
Calcium Channels, L-Type/metabolism , Elapid Venoms/pharmacology , Myocytes, Smooth Muscle/metabolism , Peptides/pharmacology , Pyloric Antrum/cytology , Aminoquinolines/pharmacology , Animals , Carbazoles/pharmacology , Cells, Cultured , Cyclic GMP/metabolism , Cyclic GMP-Dependent Protein Kinases/antagonists & inhibitors , Electrophysiology , Enzyme Inhibitors/pharmacology , Guanylate Cyclase/antagonists & inhibitors , Guinea Pigs , Intercellular Signaling Peptides and Proteins , Myocytes, Smooth Muscle/drug effects , Purinones/pharmacology , RadioimmunoassayABSTRACT
DNA adducts resulting from carcinogenic chemicals are becoming more frequently used as a powerful biomarker to determine the extent of exposure. The available techniques for determination of bulky DNA adducts can be classified into four major groups, these being immunological assay, fluorescence techniques, chromatography/m ass spectrom etry and the (32)P-postlabelling technique. In this review, the features of current techniques and the combined applications are summarized and compared. Among the available techniques, the (32)P-postlabelling assay seems to best meet the application criteria overall. In particular, (32)P-postlabelling is the most suitable technique for the detection of bulky DNA adducts induced by unknown environmental and occupational chemicals or m ixtures.
