Effects of Dendroaspis Natriuretic Peptide on Calcium-Activated Potassium Current and Its Mechanism

Abstract

Abstract:In this study, we sought to investigate the effect of dendroaspis natriuretic peptide (DNP) on calcium-activated potassium current (I K(Ca) ) and its mechanism in gastric antral circular smooth muscle cells (SMCs) using the whole-cell patchclamp technique. DNP concentration-dependently increased macroscopic I K(Ca) and spontaneous transient outward currents (STOCs) in freshly isolated guinea pig gastric antral circular SMCs. The effects of DNP on I K(Ca) and/or STOCs were not blocked by applying calcium-free bath solution or the ryanodine receptor (RyR) antagonist ryanodine (10 µM), but they were inhibited by the inositol triphosphate receptor (IP 3 R) inhibitor heparin or the guanylate cyclase inhibitor LY83583. Moreover, a DNP-induced increase in STOCs was potentiated by the cyclic guanosine monophosphate (cGMP)-sensitive phosphoesterase inhibitor zaprinast. In conclusion, our results suggest that DNP increases I K(Ca) in gastric antral circular SMCs by increasing cGMP production and activating IP 3 Rs.Key words: dendroaspis natriuretic peptide, calcium-activated potassium channels, Ca 2+ -induced Ca 2+ release, inositol 1,4,5-trisphosphate receptors, ryanodine receptor. Dendroaspis natriuretic peptide (DNP), a 38-amino residue peptide that contains a disulfide ring structure and was originally isolated from the venom of Green Mamba [6], is a new member of the natriuretic peptide family with a structure and function similar to other members. Studies about its physiological functions are limited and mainly focus on the cardiovascular [7], urinary [8], and genital systems [9]. Moreover, little is known about the functional role of DNP in gastrointestinal cells. Kim et al. [10] have for the first time demonstrated that DNP is present in rat colon and can control colonic motility as a local regulator. We have found that NPs can also regulate gastric motility [11][12][13][14]. Our further study indicates that the regulatory effect of DNP on spontaneous contraction in gastric antral circular SMCs occurs via a cGMP-dependent pathway [15]. However, the underlying mechanisms are unknown. Until now, there have been few studies about the relationship between DNP-induced increase of I K(Ca) and IP 3 Rs. In our study [16], we found that SNP increased by cGMP via IP 3 Rs. NPs are similar to nitrc oxide which is a cGMP generation system in the living body, and their physiological function exhibits very important in life science. Considering that calcium-activated potassium channels play an important role in the regulation of contractility in gastric SMCs, in this study we first intended to investigate whether DNP could affect I K(Ca) in gastric antral circular SMCs using the conventional whole-cell patch clamp technique, and then to determine the potential involvement of calcium mobilization in the effect of DNP. Moreover, the effect of cGMP on DNP-induced change of I K(Ca) was observed.