Effects of melittin on isolated papillary muscles of guinea pig.
OBJECTIVE
To investigate the effect of melittin (Mel) on papillary muscles of guinea pigs.


METHODS
Contraction of papillary muscles were examined by conventional method and action potentials (AP) were recorded by standard glass microelectrode technique.


RESULTS
Mel (0.5, 3 micromol/L) significantly increased the contractility of guinea pig papillary muscles while 5 micromol/L exerted dual action with a transient decrease followed by an increase of the contractility. Mel shortened the functional refractory period (FRP) at concentrations of 0.5, 3, and 5 micromol/L and increased the automaticity induced by adrenaline (Adr) at 3 and 5 micromol/L. Mel shifted the duration-intensity curve upward at 3 micromol/L. It shortened the action potential duration (APD) of fast action potential (FAP), decreased the action potential amplitude (APA) and resting potential (RP) at 0.5 and 3 micromol/L. As to slow action potential (SAP), Mel 0.8 micromol/L shortened APD20 and APD50, and decreased APA and RP.


CONCLUSIONS
Mel increased the contractility and automaticity of papillary muscles, shortened the FRP, decreased the excitability, shortened the APD, and decreased APA and RP of AP.
Zhang
Y L
YL
Department of Pharmacology, School of Pharmacy, Fu Dan University, Shanghai 200032, China.
Yang
S
S
Shi
N C
NC
Jiang
M H
MH
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008555:Melitten / Q000494:pharmacology*; D008839:Microelectrodes; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000502:physiology*; D012032:Refractory Period, Electrophysiological
D008555:Melitten