Isoprenaline-induced relaxation of smooth muscle not due to electrogenic sodium pumping

Ouabain or replacement of NaCl by LiCl abolishes the relaxation due to addition of KCl to sodium-rich cat carotid artery strips kept in a K+-free medium. Neither treatment antagonizes the relaxation due to β-adrenoceptor stimulation by l-isoprenaline. Unlike KCl-induced relaxation, the relaxation induced by l-isoprenaline is not due to stimulation of an electrogenic sodium pump.