title: Aqueous fraction from Costus spiralis (Jacq.) Roscoe leaf reduces contractility by impairing the calcium inward current in the mammalian myocardium.
abstract: BACKGROUND
  Brazilian folk medicine uses infusion of Costus spiralis leaf to help people to treat arterial hypertension and syndromes of cardiac hyperexcitability.
  
  
  OBJECTIVE
  Evaluate the aqueous fraction (AqF) effect on atrial contractility and investigate its mechanism of action.
  
  
  METHODS
  The AqF effect on the cardiac contractility was studied on isolated electrically driven guinea pig left atria. Atropine and tetraethylammonium (TEA) were employed to investigate whether potassium contributes for the inotropic mechanism of the AqF. The role of calcium in this effect was also studied. This was done by analysing the AqF effect on the Bowditch's phenomenon, as well as by studying whether it could interfere with the concentration-effect curve for CaCl(2), isoproterenol, and BAY K8644. Mice isolated cardiomyocytes were submitted to a whole-cell patch-clamp technique in order to evaluate whether the L-type calcium current participates on the AqF effect. Furthermore, the intracellular calcium transient was studied by confocal fluorescence microscopy.
  
  
  RESULTS
  AqF depressed the atrial contractile force. It was the most potent fraction from C. spiralis leaf (EC(50)=305 ± 41 mg/l) (crude extract: EC(50)=712 ± 41; ethyl acetate: EC(50)=788 ± 121; chloroform: EC(50)=8,948 ± 1,346 mg/l). Sodium and potassium content in the AqF was 0.15 mM and 1.91 mM, respectively. Phytochemical analysis revealed phenols, tannins, flavones, xanthones, flavonoids, flavonols, flavononols, flavonones, and saponins. Experiments with atropine and TEA showed that potassium does not participate of the inotropic mechanism of AqF. However, this fraction decreased the force overshoot characteristic of the Bowditch's phenomenon, and shifted the concentration-response curve for CaCl(2) (EC(50) from 1.12 ± 0.07 to 7.23 ± 0.47 mM) indicating that calcium currents participate on its mechanism of action. Results obtained with isoproterenol (1-1,000 pM) and BAY K8644 (5-2000nM) showed that AqF abolished the inotropic effect of these substances. On cardiomyocytes, 48mg/l AqF reduced (∼23%) the L-type calcium current density from -6.3 ± 0.3 to -4.9 ± 0.2 A/F (n=5 cells, p<0.05) and reduced the intracellular calcium transient (∼20%, 4.7 ± 1.2 a.u., n=42 cells to 3.7 ± 1.00 a.u., n=35 cells, p<0.05). However, the decay time of the fluorescence was not changed (control: 860 ± 32 ms, n=42 cells; AqF: 876 ± 26 ms, n=35 cells, p>0.05).
  
  
  CONCLUSIONS
  The AqF of C. spiralis leaf depresses myocardial contractility by reducing the L-type calcium current and by decreasing the intracellular calcium transient. Despite the lack of data on the therapeutic dose of AqF used in folk medicine, our results support, at least in part, the traditional use of this plant to treat cardiac disorders.
authors.affiliation: Laboratório de Biofísica do Coração, Departamento de Fisiologia, Universidade Federal de Sergipe, Aracaju, SE, Brazil.
authors.forename: Raquel Moreira
authors.initials: RM
authors.lastname: Britto
authors.forename: André Luiz
authors.initials: AL
authors.lastname: Santos
authors.forename: Jader Santos
authors.initials: JS
authors.lastname: Cruz
authors.forename: Antonio Nei Santana
authors.initials: AN
authors.lastname: Gondim
authors.forename: Sandra
authors.initials: S
authors.lastname: Lauton-Santos
authors.forename: Aline
authors.initials: A
authors.lastname: Lara
authors.forename: Silvia
authors.initials: S
authors.lastname: Guatimosim
authors.forename: Carla Maria Lins
authors.initials: CM
authors.lastname: Vasconcelos
authors.forename: Charles Dos Santos
authors.initials: Cdos S
authors.lastname: Estevam
authors.forename: Antonio Santos
authors.initials: AS
authors.lastname: Dias
authors.forename: Evaleide Diniz
authors.initials: ED
authors.lastname: Oliveira
authors.forename: Adriana Karla
authors.initials: AK
authors.lastname: Lima
authors.forename: Rejane Cardoso
authors.initials: RC
authors.lastname: Souza
authors.forename: Eduardo Antonio
authors.initials: EA
authors.lastname: Conde-Garcia
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D029770:Costus / Q000737:chemistry*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009200:Myocardial Contraction / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D010936:Plant Extracts / Q000494:pharmacology*
chemical_list: D020746:Calcium Channels, L-Type; D010936:Plant Extracts; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D007545:Isoproterenol