Cytosolic calcium staircase in ventricular myocytes isolated from guinea pigs and rats.
OBJECTIVE
The aim was to study intracellular calcium dynamics underlying positive or negative tension staircase of mammalian hearts.


METHODS
Changes in cytosolic calcium concentration [( Ca2+]i) in single ventricular myocytes were investigated using a Ca2+ indicator, fura-2. Beat to beat alterations in fura-2 fluorescence and cell edge movement on resumption of stimulation were recorded on video tape, and analysed by a computer based image processing system.


METHODS
Single ventricular myocytes were enzymatically isolated from the hearts of 30 adult guinea pigs and 25 adult rats.


RESULTS
In guinea pig ventricular myocytes, the positive contractile staircase was associated with ascending staircases of both peak systolic and end diastolic [Ca2+]i because of a cumulative increase in diastolic [Ca2+]i. In rat ventricular myocytes, the negative contractile staircase was accompanied by a descending staircase of peak systolic [Ca2+]i, while end diastolic [Ca2+]i level was unchanged due to the rapid decay of [Ca2+]i transients. Ryanodine (10 microM) reversed the mode of [Ca2+]i and contractile staircases from negative to positive in rat myocytes, whereas it caused minimal alteration in guinea pig myocytes.


CONCLUSIONS
Tension staircase of mammalian hearts depends on diastolic Ca2+ level as well as Ca2+ handling by the sarcoplasmic reticulum. The positive staircase may require progressive increase in diastolic [Ca2+]i, while the negative staircase may be mediated by depletion of activator Ca2+ in the sarcoplasmic reticulum.
Hattori
Y
Y
Department of Circulation and Respiration, Nagoya University, Japan.
Toyama
J
J
Kodama
I
I
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism*; D016257:Fura-2; D006168:Guinea Pigs; D006352:Heart Ventricles; D007091:Image Processing, Computer-Assisted; D008856:Microscopy, Fluorescence; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D014741:Video Recording
D002118:Calcium; D016257:Fura-2