[Effects of ketamine on K+-contracture in isolated vascular smooth muscle from rabbit]

The effects of ketamine on contraction induced by depolarization of cell membrane (high K+-induced contracture) were studied in isolated vascular smooth muscle from rabbit portal vein. Ketamine in concentrations above 5 x 10(-4) M caused relaxation in phasic contraction, and above 10(-4) M caused relaxation in tonic contraction. These effects of ketamine at concentrations of between 10(-5) to 10(-3) M were dose dependent and reversible. In concentration above 10(-5) M, ketamine decreased the contractile response (tonic contraction) induced by 2.5 mM Ca2+ after the temporary contracture in Ca2+-free, high K+ solution. The contractile responses to norepinephrine (10(-6) M) or serotonin (10(-6) M) were also inhibited by ketamine. From these findings, it is concluded that ketamine decreases contractile responses due to transmembrane Ca2+ influx after depolarization of cell membrane and may decrease the contractile responses in concentration above 5 x 10(-4) due to Ca2+ release inhibition from sarcoplasmic reticulum.