Portal de Periódicos da CAPES

Preponderance of postsystolic period in the positive inotropic effects of increases in (Ca++).

1975; National Institutes of Health; Volume: 8; Linguagem: Inglês

Wood Eh, Allen Dg, Jewell Br,

Cardiovascular and exercise physiology

If the frequency of stimulation of isolated kitten right ventricular papillary muscles is progressively reduced, the size of contractions decreases until a frequency is reached (rested state rate) where further reduction produces no change (rested state contraction, Koch-Weser and Blinks, 1963). At 30 degrees C and 2.25 mM Ca++, the rested state rate was about one per 2-5 min, the peak tension of 0.2-0.6 g/mm2 was about 5-15% of the tension of 20/min beats, and times to peak tension and 80% repolarization about doubled. Sudden calcium increases in the perfusion fluid, [Ca++]p, from 2.25 to 6.75 mM were produced at random during intervals between rested state contractions, and time and amplitude of peak isometric tension, max +/- dT/dt of subsequent beats were studied. The greatest positive inotropic response of the initial beats following increments in [Ca++]p resulted when [Ca++]p was increased immediately after a rested state contraction: as the postsystolic interval before the [Ca++]p increment was increased, the positive inotropic effects decreased approximately exponentially, attaining a plateau level in about 30 sec. This plateau was then maintained until the period prior to the initial test beat in high calcium was less than the approximately 2-min diffusion equilibrium time between [Ca++]p and the interior of the fiber.