The effect of Ca²⁺ channel antagonists (cadmium, ω-conotoxin GIVA, and nitrendipine) on the release of angiotensin II from fetal rat brain in vitro

We have shown previously that K⁺ stimulation of dissociated cell cultures of fetal rat brain results in a graded release of angiotensin II (ANG II) that is dependent on the availability of extracellular Ca²⁺. In this study, using dissociated cell cultures of fetal rat hypothalamus, thalamus, septum, and midbrain (HTSM), we further examined the role of calcium channels on ANG II release using specific channel blockers (cadmium, ω-conotoxin, and nitrendipine) and a calcium ionophore (A23187). Levels of ANG II release were quantitated by radioimmunoassay and HPLC. For control levels of ANG II release, cells were incubated in a stock buffer containing 89 mM choline chloride/58 mM KCl/2 mM CaCl₂. Pretreatment of the cells with either 100 μM Cd²⁺ (to block N-, L-, and T-type calcium channels), 100 nM ω-conotoxin (to block N- and L-type calcium channels), or 500 nM nitrendipine (to block L-type calcium channels) decreased ANG II release by approximately 71%, 71%, and 22%, respectively, when compared to control levels. In contrast, pretreatment of the cells with 1.6 μM A23187 (a calcium ionophore) increased ANG II release by approximately 90% over control levels. These findings suggest that angiotensin release is dependent on the intracellular entry of Ca²⁺ ions through primarily N-type channels, and to a lesser extent, L-type channels.