Actions of 8-(N,N-diethylamino)-n-octyl-3,4,5-trimethoxybenzoate in vascular smooth muscle cell cultures

Abstract

Aim: To study the effects of 8-(N,N-diethylamino)-n-octyl-3,4,5-trimethoxybenzoate (TMB-8) on vascular smooth muscle (VSM) cells A7r5.

Methods: The effects of TMB-8 were investigated in A7r5 cell cultures with 45CaCl2.

Results: TMB-8 reduced the intracellular free Ca2+ concentration, [Ca2+]i in a Ca(2+)-free medium and blocked Ca2+ entry from the extracellular site in a regular Ca2+ medium. The equilibrated total cellular binding of Ca2+ was increased by TMB-8 whereas 45Ca2+ entry activated by both NE and KCl was inhibited. However, the NE-activated Ca2+ entry was not blocked by TMB-8 if TMB-8 was added together with 45Ca2+ at a later time instead of by pretreatment. Similar to actions 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 plus TMB-8 in VSM cells, the inhibitory effect of TMB-8 was not affected.

Conclusion: TMB-8 not only blocks Ca2+ entry from the extracellular site, but also enhances Ca2+ uptake into SR which, indirectly inhibits Ca2+ entry from the extracellular site.