ACTIONS OF N,N-DIETHYLAMINO)-N-OCTYL-3,4,5-TRIMETHOXYBENZOATE IN VASCULAR SMOOTH-MUSCLE CELL-CULTURES

AIM: To study the effects of N,N-diethylamino)-n-octyl-3,4,5-trimethox ybenzoate (TMB-8) on vascular smooth muscle (VSM) cells A7r5. METHODS: The effects of TMB-8 were investigated in A7r5 cell cultures with (Ca Cl2)-Ca-45. RESULTS: TMB-8 reduced the intracellular free Ca2+ concent ration, [Ca2+](i) in a Ca2+-free medium and blocked Ca2+ entry from th e extracellular site in a regular Ca2+ medium. The equilibrated total cellular binding of Ca2+ was increased by TMB-8 whereas Ca-45(2+) entr y activated by both NE and KCl was inhibited. However, the NE-activate d Ca2+ entry was not blocked by TMB-8 if TMB-8 was added together with Ca-45(2+) at a later time instead of by pretreatment. Similar to acti ons of NE and KCl, depletion of Ca2+ from sarcoplasmic reticulum (SR) would also activate Ca2+ entry, which was blocked by TMB-8. When TMB-8 was rinsed out alone or together with NE after pretreatment with NE p lus TMB-8 in VSM cells, the inhibitory effect of TMB-8 was not affecte d. CONCLUSION: TMB-8 not only blocks Ca2+ entry from the extracellular site, but also enhances Ca2+ uptake into SR which, indirectly inhibit s Ca2+ entry from the extracellular site.