Nitric Oxide Function in an Echinoderm.

Area of Science:

• Marine Biology
• Biochemistry
• Physiology

Background:

• Nitric oxide (NO) synthesized from L-arginine by NO synthase (NOS) regulates smooth muscle relaxation via cyclic-GMP (cGMP) in vertebrates.
• The NO-cGMP pathway's role in non-vertebrate smooth muscle regulation is less understood.

Purpose of the Study:

• To investigate the presence and function of the NO-cGMP pathway in the cardiac stomach of the starfish Asterias rubens.
• To determine if NO signaling regulates smooth muscle tone in echinoderms.

Main Methods:

• Administered NO donors (hydroxylamine, SNOG, SNAP) and L-arginine to starfish cardiac stomach preparations.
• Utilized inhibitors of soluble guanylyl cyclase (ODQ) and NO synthase (L-NMMA) to probe the NO-cGMP pathway.
• Observed effects on cardiac stomach muscle tone (relaxation/contraction).

Main Results:

• NO donors and L-arginine induced relaxation of the starfish cardiac stomach.
• The relaxing effects were inhibited by ODQ and L-NMMA, confirming NO-cGMP pathway involvement.
• Inhibition of NO or SGC signaling led to cardiac stomach contraction.

Conclusions:

• The NO-cGMP pathway is present and functional in the starfish cardiac stomach, regulating smooth muscle relaxation.
• This signaling pathway is conserved beyond vertebrates, occurring in echinoderms.
• NO-cGMP-mediated relaxation likely plays a role in starfish feeding behaviors, such as stomach eversion.