Nitric oxide activates voltage-dependent potassium currents of crustacean skeletal muscle

Nitric oxide (NO), a radical gas, acts as a multifunctional intra- and inte rcellular messenger. In the present study we investigated the effects of NO on muscle membrane potassium currents of isolated single muscle fibers fro m the marine isopods, Idotea baltica, using two-electrode voltage clamp rec ording techniques. Voltage-activated potassium currents consist of an outwa rd current with fast activation and inactivation kinetics and a delayed, pe rsistent outward current. Both currents were blocked by extracellular 4-ami nopyridine and tetraethylammonium; the currents were not blocked by charybd otoxin or apamin. Application of the NO donors S-nitroso-N-acetylpenicillam ine (SNAP) or hydroxylamine increased both the early and the delayed outwar d current in a dose- and time-dependent manner. PTIO, a NO scavenger, suppr essed the effect of SNAP. N-Acetyl-DL-penicillamine, a related control comp ound which does not liberate NO, had no significant effect on outward curre nts. Methylene blue, a guanylyl cyclase inhibitor, prevented the increase o f the outward current while 8-bromo-cGMP increased the current. Our experim ents show that potassium currents of Idotea muscle are increased by NO dono rs. They suggest that NO by stimulating cGMP production mediates the effect s on membrane currents involved in regulation of invertebrate muscle excita bility. (C) 2001 Academic Press.