Dendroaspis natriuretic peptide relaxes gastric antral circular smooth muscle of guinea-pig through the cGMP/cGMP-dependent protein kinase pathway

Abstract

Aim: To systematically investigate if cGMP/cGMP-dependent protein kinase G (PKG) signaling pathway may participate in dendroaspis natriuretic peptide (DNP)-induced relaxation of gastric circular smooth muscle.

Methods: The content of cGMP in guinea pig gastric antral smooth muscle tissue and perfusion solution were measured using radioimmunoassay; spontaneous contraction of gastric antral circular muscles recorded using a 4-channel physiograph; and Ca(2+)-activated K(+) currents (I(K(Ca))) and spontaneous transient outward currents (STOCs) in isolated gastric antral myocytes were recorded using the whole-cell patch clamp technique.

Results: DNP markedly enhanced cGMP levels in gastric antral smooth muscle tissue and in the perfusion medium. DNP induced relaxation in gastric antral circular smooth muscle, which was inhibited by KT5823, a cGMP-dependent PKG inhibitor. DNP increased I(K(Ca)). This effect was almost completely blocked by KT5823, and partially blocked by LY83583, an inhibitor of guanylate cyclase to change the production of cGMP. DNP also increased STOCs. The effect of DNP on STOCs was abolished in the presence of KT5823, but not affected by KT-5720, a PKA-specific inhibitor.

Conclusion: DNP activates I(K(Ca)) and relaxes guinea-pig gastric antral circular smooth muscle via the cGMP/PKG-dependent singling axis instead of cAMP/PKA pathway.

Figure 1

A: Effect of 10 nmol/L LY83583 on cGMP production of in tissue (n = 8), ^bP < 0.01 vs control group, ^dP < 0.01 vs DNP group; B: Effect of 10 nmol/L LY83583 on cGMP production of in efflux (n = 8), ^fP < 0.01 vs control group, ^hP < 0.01 vs DNP group; C: Effect of a membrane-permeable PKG-specific inhibitor (KT5823) on DNP-induced inhibition of spontaneous contraction in gastric antral circular smooth muscle (n = 8), ^jP < 0.01 vs DNP group.

Figure 2

Effect of LY83583 on DNP-induced increase of I_K(Ca), ^bP < 0.01 vs control group.

Figure 3

Effect of a membrane-permeable PKG-specific inhibitor, KT-5823, on DNP-induced increase of I_K(Ca) (n = 8), ^bP < 0.01 vs control group.

Figure 4

A: Effect of a membrane-permeable PKG-specific inhibitor, KT-5823, on STOCs (n = 10); B: Effect of KT-5720 (500 nmol/L), a PKA-specific inhibitor, on STOCs (n = 10).