Effects of low concentration of dihydroouabain on intracellular calcium in guinea pig ventricular myocytes

The effects of low concentration of dihydroouabain (DHO) on intracellular calcium concentration ([Ca 2+ ] i) were investigated in guinea pig ventricular myocytes. [Ca 2+ ] i was detected by confocal microscopy and represented by fluorescent intensity. DHO (1 fmol/L～1 mmol/L) increased [Ca 2+ ] i, especially at 10 pmol/L. Nisoldipine, egtazic acid, or tetrodotoxin partially inhibited the effect of 10 pmol/L DHO on [Ca 2+ ] i. The effects of DHO remained in the absence of extracellular K + and Na +. These results suggest that low concentration of DHO might increase [Ca 2+ ] i via the receptor operated Ca 2+ channels, TTX sensitive Na + channels or/and triggering of intracellular calcium release; Na +/K + pump and Na +/Ca 2+ exchange seem not involved in the effect of DHO.