Intracellular and extracellular angiotensin II enhance the L-type calcium current in the failing heart.

The influence of intracellular and extracellular angiotensin II (Ang II) on the L-type calcium current of cardiomyocytes isolated from cardiomyopathic hamsters was investigated. The results indicated that Ang II (10(-8) mmol/L), added to the bath, increased the peak inward calcium current (I(Ca)) density by 37+/-3.4% (P<0.05), an effect that depends on the activation of protein kinase C. Intracellular administration of the same dose of Ang II (10(-8) mmol/L) also elicited an increase of peak I(Ca) density but enhanced the rate of I(Ca) inactivation, an effect not seen with extracellular Ang II. Moreover, in control animals, no change in the rate of I(Ca) inactivation was seen with intracellular Ang II. Thapsigargin (1 micromol/L), a potent inhibitor of sarcoplasmic reticulum (SR) ATPase, which depletes the SR, decreased the rate of I(Ca) inactivation elicited by intracellular Ang II, although the cytoplasmic calcium concentration was highly buffered with 10 mmol/L EGTA. These findings might indicate that intracellular Ang II releases calcium from the SR and inactivates I(Ca). The effect of intracellular Ang II on peak I(Ca) was not altered by extracellular losartan (10(-7) mmol/L), supporting the notion that the peptide acted intracellularly. Other studies showed that intracellular Ang I administration (10(-8) mmol/L) enhanced the peak I(Ca) density and the rate of I(Ca) inactivation, an effect that was reduced by intracellular enalaprilat (10(-8) mmol/L). Moreover, intracellular enalaprilat by itself reduced the peak I(Ca) density. These observations might indicate that endogenous Ang II is contributing to I(Ca) modulation in the failing heart.

New polymer-based prepacked column for the reversed-phase liquid chromatographic separation of peptides over the pH range 2-12.

The aim of this paper was to investigate the properties of a new column, Source 5RPC, for the separation of peptides at pH 2, 4.5, 7, 9 and 12 and to compare this product with similar polymer-based products available on the market. All columns were prepacked with 5 microm polystyrene-divinylbenzene polymer bead matrices and had dimensions of 150x4.6 mm I.D. Separations of angiotensin peptides were achieved on these columns using different equilibration solvents in the pH range 2-12 and elution with acetonitrile gradients. The separation of the peptide mixture obtained on Source 5RPC column was compared with that of two other commercially available polymer-based matrices. Method scouting and optimisation were carried out using the novel chromatography system, AKTA purifier.

Angiotensin II analogues. 13. Role of the hydroxyl group of position 4 tyrosine in pressor activity.

In order to determine the features of the phenolic ring in position 4 of [Asn1,Ile5]angiotensin II that contribute to pressor activity, analogues with selected aromatic substituents were synthesized by the solid-phase method. They showed pressor activities in the rat: [Asn1,Phe(4-NH2)4]AII, 24%; [Asn1,Phe(4-NO2)4AII, 0.1%; [Asn1,Tyr(3,5-Me2)4]AII, 2.2%; [Asn1,D-Tyr(3,5-Me2)4]AII, 1.4%. These results indicate that the activity contributed by the aromatic character of the phenyl ring in the side chain of position 4 is enhanced by a group in the para position that may function as a proton donor in hydrogen-bond formation. Bulky substituents ortho to this hydrogen-bonding group decrease activity by steric interference with hydrogen-bond formation. Bulky groups than cannot act as hydrogen donors in the para position of the aromatic ring drastically decrease the activating effect of the aromatic ring on pressor activity.