ACTIONS OF CADP-RIBOSE AND ITS ANTAGONISTS ON CONTRACTION IN GUINEA-PIG ISOLATED VENTRICULAR MYOCYTES - INFLUENCE OF TEMPERATURE

Although it is becoming widely accepted that cADP-ribose (cADPR) can r egulate calcium release from the endoplasmic reticulum in sea urchin e ggs and in a variety of mammalian cell types, it remains controversial whether this substance might influence calcium release during excitat ion-contraction coupling in cardiac muscle. We have investigated possi ble actions of cADPR in intact cells isolated from guinea pig ventricl e, paying particular attention to the possible influence of temperatur e. At 36 degrees C, myocyte contraction was influenced by cytosolic ap plication of cADPR in a concentration-dependent manner (showing an app roximate to 30% increase in contraction with 5 mu mol/L cADPR applied via a patch pipette in myocytes stimulated to fire action potentials a t 1 Hz). Calcium transients measured with fura 2 were also increased b y 5 mu mol/L cADPR. Antagonists of cADPR reduced contraction at 36 deg rees C (by approximate to 35% with either 50 mu mol/L 8-Br-cADPR or 5 mu mol/L 8-amino-cADPR applied via the patch pipette). At room tempera ture (approximate to 20 degrees C to 24 degrees C), no significant eff ects on contraction were detected with either cADPR or its antagonists . At 36 degrees C, treatment of the cells with a mixture of 2 mu mol/L ryanodine and 1 mu mol/L thapsigargin to suppress function of the sar coplasmic reticulum stores of calcium prevented the action of 5 mu mol /L cADPR applied via a patch pipette. These observations are consisten t with an action of cytosolic cADPR to enhance calcium-induced calcium release from the sarcoplasmic reticulum in guinea pig ventricular myo cytes at 36 degrees C. The observed influence of temperature under the conditions of our experiments is one factor that might help to accoun t for failure to detect actions of cADPR and its analogues in some pre vious studies.