Voltage dependent fast calcium current in cultured skeletal myocytes of the frog Rana temporaria.
Voltage dependent calcium currents in cultured frog embryonic skeletal myocytes at stages of development ranging from 2 to 9 days were studied using the whole-cell patch clamp technique at 19-21 degrees C. Membrane currents were recorded in the presence of 2 mmol/l Ca2+ (outside), and 60 mmol/l CsCl and 50 mmol/l TEACl (inside). In the absence of sodium current two components of inward current were observed in response to depolarization already during the early stages of myogenesis: the well-known slow dihydropyridine (DHP)-sensitive calcium current (ICa,s), and a fast-activated current. Both components persisted in the presence of 2 mumol/l tetrodotoxin. The fast-activated component was enhanced upon addition of 6 mmol/l Ca2+ or Ba2+ to the external recording solution and was decreased when the standard external solution was replaced by Ca2+ free solution. Thus, the fast component of the inward current was also carried by Ca2+ (ICa,f). Unlike ICa,s, it was not blocked with 30-150 mumol/l DHP nifedipine. During 7 s depolarization ICa,f was detected at approximately -50 mV, 20 mV more negative than the membrane potentials at which ICa,s appeared. At various test potentials t0.5 for activation of ICa,f was 8-20 ms, and the current declined during depolarization with tau in of 500-800 ms. These results indicate the existence of two types of voltage-dependent Ca2+ channels in early stages of development of frog myocytes, both known in mature frog skeletal muscle fibres.
Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of Russia, St. Petersburg.
V
V
Lukyanenko
I E
IE
Katina
G A
GA
Nasledov
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D004625:Embryo, Nonmammalian / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D018482:Muscle, Skeletal / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011896:Rana temporaria; D013779:Tetrodotoxin / Q000494:pharmacology
D015220:Calcium Channels; D013779:Tetrodotoxin; D015761:4-Aminopyridine; D009543:Nifedipine