Inhibitory effect of 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) in vascular smooth muscle

Abstract

The inhibitory effects of 8-(N,N-diethylarnmo)octyl-3,4,5-trirnethoxybenzoate (TMB-8) on vascular smooth muscle contraction and cytosolic Ca 2+ level ([Ca 2+] i) were examined using isolated rabbit aorta loaded with a fluorescent Ca 2+ indicator, fura-2. TMB-8 (100 μM) decreased the high K +-induced increase in muscle tension, and [Ca 2+] i and 45Ca 2+ influx to their respective resting levels. TMB-8 (100 μM) almost completely inhibited the increase in [Ca 2+] i and 45Ca 2+ influx due to norepinephrine although muscle tension was only partially decreased. A higher concentration of TMB-8 (300 μM) inhibited the remaining portion of the contraction without additional decrease in [Ca 2+] i. The inhibitory effect of TMB-8 on high K +-induced contraction, but not on the norepinephrine-induced contraction, was antagonized by the increase in external Ca 2+ concentrations or by the Ca 2+ channel activators, CGP 28,392 and by Bay K8644. In Ca 2+-free solution, norepinephrine-induced transient increases in [Ca 2+] i and muscle tension and 100 μM TMB-8 inhibited these changes. The caffeine-induced transient increases in [Ca 2+] i and muscle tension were also inhibited by TMB-8 at concentrations higher than those needed to inhibit the norepinephrine-induced transient changes. In permeabilized smooth muscle, TMB-8 (300 μM) did not inhibit the Ca 2+-induced contraction. These results suggest that TMB-8 inhibits vascular smooth muscle contractility by inhibiting Ca 2+ influx, Ca 2+ release and Ca 2+ sensitization of contractile elements.