Angiotensin I Modulates Ca-transport Systems in the Rat Heart Through Angiotensin II

The objective of this study was to determine the effect of angiotensin I (Ang I) treatmentin vivoon two major Ca-transport systems—the -type voltage dependent calcium channel ( -VDCC) and the Na/Ca exchanger in rat heart. For our experiments we used four groups of rats, treated differently with saline, Ang I, the ACE inhibitor enalapril and/or combination of both for 6 days, every 24 h. We observed an increase in the activity, and also in mRNA expression of the Na/Ca exchanger, after repeated administration of Ang Iin vivo. The maximal binding capacity of Ca-antagonist PN 200-110, which binds to theα1subunit of the -VDCC was elevated from 0.8–1.85 pg/mg protein. mRNA expression of the voltage-dependent calcium channels of -type system was also upregulated by Ang I administration, but not when enalapril was applied simultaneously with Ang I. These results demonstrate thatin vivoapplication of the Ang I significantly modulates not only the activity, but also expression of the Na/Ca exchanger and the -VDCC in rat hearts through angiotensin II (Ang II). Since in thein vitroexperiments on the isolated cardiomyocytes, Ang II (100 n ) increased the calcium uptake after depolarization, and the AT1receptor agonist losartan prevented this increase, we assume that this regulation might involve the AT1receptors.