Relaxation induced by KCl, NaCl and sucrose in rabbit coronary arteries.

Contractions induced in isolated ring segments of rabbit coronary arteries by 2-(2-aminoethyl)-pyridine (AEP) were transiently relaxed when KCl, NaCl or sucrose were added to the bathing solution without osmotic correction. When these solutes were added with osmolarity changes minimized by reducing the concentration of another constituent of the medium the relaxations were reduced or abolished. AEP contraction was associated with depolarization and solute-induced relaxation with a lessening of the depolarization. Ouabain depolarized the vessel and diminished both the relaxation and repolarization induced by hyperosmolar addition of NaCl and sucrose to AEP-contracted segments. Sucrose and NaCl also relaxed potassium-induced contractions and their effect was greater at [K]o 25 mM than at [K]o 60 mM. Hyperosmolar relaxation still occurred but was significantly smaller in vessels subjected to prolonged sodium pump inhibition produced by cold storage followed by re-warming in K-free or ouabain-containing solution. It is concluded that hyperosmolar relaxation is mainly due to hyperpolarization and is influenced by the level of membrane potential. The inhibition of hyperosmolar relaxation by ouabain may be due to its depolarizing action.