Effects of strophanthidin on intracellular Ca2+ concentration and cellular morphology of guinea pig myocytes

To study the role of cytosolic calcium concentration [( Ca2+]i) in the pathophysiology of Ca2+ overload, we used a digital image of calcium indicator signals (fura-2 fluorescence) from guinea pig myocytes. [Ca2+]i increased from 69(SEM 5) nmol.litre-1 (n = 15) to 204(45) nmol.litre-1 (n = 14) after 10 min perfusion with 100 mumol.litre-1 strophanthidin. The effects of strophanthidin on cellular morphology were associated with variable increases in [Ca2+]i of myocytes. [Ca2+]i was 263(9) nmol.litre-1 in the spontaneous contracting cells with "Ca2+ wave", and 784(103) nmol.litre-1 in rounded cells. There was a significant relationship (r = 0.77, p less than 0.001) between elevation of [Ca2+]i and shortening of longitudinal length of the cells. After 20 min pretreatment with 10 mumol.litre-1 ryanodine, strophanthidin (100 mumol.litre-1) did not cause spontaneous contractile activity, and induced a slower increase in [Ca2+]i than found previously with strophanthidin alone. We suggest that [Ca2+]i played a primary role in mediating irreversible injury in this study, and that the absolute value of [Ca2+]i was correlated with morphological changes. We also suggest that the Ca2+ release from the sarcoplasmic reticulum was related to the increase in [Ca2+]i and the spontaneous contracting activity.