[Changes in cell membrane excitability during guinea pig papillary muscle after-contractions].
In isolated guinea-pig papillary muscles, the excitability of cellular membrane was investigated during the after contractions induced by cooling of the perfusate to 13--15 degrees C, addition of noradrenaline (2 mg/l), and calcium to 16 MM. At stimulation rate 0.2 Hz the oscillation amplitude was 19 +/- 2% of the initial contraction. The activity of the fast sodium channels was estimated by the threshold for AP initiation and appeared to increase gradually after the end of AP. Slow channel response measured in the high potassium solution (29 MM), significantly decreased during the after contraction. Even at supramaximal amplitude of stimulation the slow responses were about 10--20 mV smaller than those after or before oscillation. Slow channel activity seems to depend on intracellular calcium concentration. Oscillations after contractions were abolished by addition of caffeine (2 mM). The oscillations seem to result from recirculation of calcium between myoplasma and sarcoplasmatic reticulum.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D006168:Guinea Pigs; D007473:Ion Channels / Q000502:physiology; D009129:Muscle Tonus / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology*
D007473:Ion Channels; D002118:Calcium; D009638:Norepinephrine
Izmenenie vozbudimosti kletochnoĭ membrany vo vremia ostsilliatsii tonusa papilliarnoĭ myshtsy morskoĭ svinki.