Actions of cADP-Ribose and Its Antagonists on Contraction in Guinea Pig Isolated Ventricular Myocytes Influence of Temperature

Abstract Although it is becoming widely accepted that cADP-ribose (cADPR) can regulate calcium release from the endoplasmic reticulum in sea urchin eggs and in a variety of mammalian cell types, it remains controversial whether this substance might influence calcium release during excitation-contraction coupling in cardiac muscle. We have investigated possible actions of cADPR in intact cells isolated from guinea pig ventricle, paying particular attention to the possible influence of temperature. At 36°C, myocyte contraction was influenced by cytosolic application of cADPR in a concentration-dependent manner (showing an ≈30% increase in contraction with 5 μmol/L cADPR applied via a patch pipette in myocytes stimulated to fire action potentials at 1 Hz). Calcium transients measured with fura 2 were also increased by 5 μmol/L cADPR. Antagonists of cADPR reduced contraction at 36°C (by ≈35% with either 50 μmol/L 8-Br-cADPR or 5 μmol/L 8-amino-cADPR applied via the patch pipette). At room temperature (≈20°C to 24°C), no significant effects on contraction were detected with either cADPR or its antagonists. At 36°C, treatment of the cells with a mixture of 2 μmol/L ryanodine and 1 μmol/L thapsigargin to suppress function of the sarcoplasmic reticulum stores of calcium prevented the action of 5 μmol/L cADPR applied via a patch pipette. These observations are consistent with an action of cytosolic cADPR to enhance calcium-induced calcium release from the sarcoplasmic reticulum in guinea pig ventricular myocytes at 36°C. The observed influence of temperature under the conditions of our experiments is one factor that might help to account for failure to detect actions of cADPR and its analogues in some previous studies.