[The double effect of myocardial stimulation].
The stimulus generated at the sinus node induces on the heart working cells a stronger contraction at higher frequences. The purpose of the present report is to investigate whether the two effects a) exicitation-contraction coupling and b) contraction strength are independent. Instead of the pace-maker it has been used a rectangular waves generator; the pulses are applied to isolated guinea-pig auricle or rat right ventricle. The AA. show a stronger twitch of cell when the membrane is depolarized without contraction. This phenomenon can be obtained as follows: by applying peculiar conditions of high frequency train pulses (so that they are not capable of eliciting contraction) or depolarizing the membrane with high KO concentration. The AA. believe that the stronger contraction of the muscle cell is due to the depolarization generated by the stimulus and it is not connected to the contraction. The potentiating factor is independent by cAMP and cytoplasmic Ca++. This factor is antagonized by propranolol.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D006168:Guinea Pigs; D009200:Myocardial Contraction / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats
D011433:Propranolol; D011188:Potassium; D002118:Calcium
Il doppio effetto dello stimolo sul miocardio.