Three types of slow inward currents as distinguished by melittin in 3-day-old embryonic heart.
Membrane slow inward currents of 3-day-old embryonic chick single heart cells were investigated using the whole-cell patch clamp technique. In a solution containing only Na+ ions and in the presence of tetrodotoxin and Mn2+, the inward current-voltage relationship presented two maxima, confirming the existence of two different voltage-dependent slow inward currents. The first type, a fast transient slow inward current (Isi (ft], was activated from a holding potential of -80 mV and showed fast activation and inactivation. This current was highly sensitive to melittin (10(-8) M) and insensitive to low concentrations of desmethoxyverapamil [-)D888, 10(-9)-10(-6) M). Depolarizing voltage steps from a holding a potential of -50 mV activated two components of the slow inward current, i.e., a slow and a sustained current (Isi(sts] that showed a slow inactivation followed by a slow inactivation and a sustained component. Melittin at a high concentration (10(-4)M) completely blocked the slow transient component (Isi(st] and left unblocked the sustained component (Isi(s]. Both components (Isi(st) and Isi(s] were blocked by verapamil (10(-5)M) and low concentrations of (-)D888 (10(-8)-10(-6)M).
Bkaily
G
G
Department of Physiology and Biophysics, Faculty of Medicine, Université de Sherbrooke, Qué, Canada.
Jacques
D
D
Yamamoto
T
T
Sculptoreanu
A
A
Payet
M D
MD
Sperelakis
N
N
D000818:Animals; D001514:Bee Venoms / Q000494:pharmacology*; D002642:Chick Embryo; D004594:Electrophysiology; D006321:Heart / Q000187:drug effects* / Q000196:embryology; D008345:Manganese / Q000494:pharmacology; D008555:Melitten / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014700:Verapamil / Q000031:analogs & derivatives / Q000494:pharmacology
D001514:Bee Venoms; D008555:Melitten; D008345:Manganese; D013779:Tetrodotoxin; C043184:4-desmethoxyverapamil; D012964:Sodium; D014700:Verapamil