153rCgA1–64S-S). These experiments revealed that the presence of the disulfide bridge
is required for the cardiotropic action of VSs. In accordance with the experiments
performed on the Langendorff isolated heart (Cerra et al. 2008 ), rCgA1–64S-S
dose-dependently reduced papillary muscle contractility both under basal condi-
tions and after β-adrenergic stimulation. However, neither rCgA1–64SH nor CgA1–
64OX affected papillary muscle inotropism.
On the basis of previous observations suggesting that the effects of hrVS-1
mainly depend on the activation of the PI3K-Akt-NO pathway and NO release from
endothelial cells (Gallo et al. 2007 ) (see also below for further details), the effect of
rCgA1–64S-S were studied in papillary muscles treated with NG-nitro-L-arginine
methyl ester (L-NAME) or with wortmannin (Wm). Pharmacological blockade of
both NO synthesis or PI3K activation abrogated the negative inotropic effect of
rCgA1–64S-S, suggesting that the PI3K-Akt-NO pathway plays an important role
in the inotropic effect induced by VSs.
2.2 Catestatin
The experiments performed on the isolated rat heart showed that, in contrast to
VS-1, in basal conditions CST increased heart rate and coronary resistances in a
dose-dependent manner, suggesting that these two peptides may display specific
different activities in this preparation. On the other hand, CST caused a vasorelaxant
influence when coronary arteries were pre-contracted by endothelin-1 (ET-1),
through a Gi/o protein–NO–cGMP-dependent mechanism (Angelone et al. 2008 ).
CST (10–50 nM) induced a biphasic effect on isolated rat papillary muscle, charac-
terized by an early transient increase in contractile force, followed by a negative,
antiadrenergic effect, similar to that previously reported for the isolated heart
(Bassino et al. 2011 ). Under basal conditions, while a low concentration (5 nM) of
CST had no significant effect on myocardial contractility, higher concentrations
(10–50 nM) induced a transient positive inotropic effect, reaching near to 50% over
control, which was completely reverted within a few minutes. The early positive
effect of CST was probably caused by histamine release from cardiac mast cells and
H 1 receptors activation (for further details, see below). At concentrations between
5–50 nM, CST exerted a significant anti-adrenergic effect, which was blocked by
inhibition of PI3K, NO synthesis or cGMP, thus suggesting that, as in the case of
VSs, PI3K, NO and cGMP play an important role in the cardiac effects induced by
CST. Additional experiments have been performed to study the effects of two natu-
rally occurring variants of CST (G364S-CST and P370L-CST). In basal conditions,
the effects of both G364S-CST and P370L-CST were comparable to that induced by
WT-CST, being ineffective at a low concentration (5 nM), while higher concentra-
tions (10–50 nM) induced a transient positive inotropic effect. However, only
P370L-CST was able to reduce the positive inotropic effect exerted by β-adrenergic
stimulation, while G364S-CST failed to modulate the effect of Isoproterenol (Iso)
(Bassino et al. 2011 ).
Signalling Pathways of CgA-Derived Peptides in Cardiac and endothelial cells