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

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 degrees C, myocyte contraction was influenced by cytosolic application of cADPR in a concentration-dependent manner (showing an approximately 30% increase in contraction with 5 mumol/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 mumol/L cADPR. Antagonists of cADPR reduced contraction at 36 degrees C (by approximately 35% with either 50 mumol/L 8-Br-cADPR or 5 mumol/L 8-amino-cADPR applied via the patch pipette). At room temperature (approximately 20 degrees C to 24 degrees C), no significant effects on contraction were detected with either cADPR or its antagonists. At 36 degrees C, treatment of the cells with a mixture of 2 mumol/L ryanodine and 1 mumol/L thapsigargin to suppress function of the sarcoplasmic reticulum stores of calcium prevented the action of 5 mumol/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 degrees 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.

An Antagonist of cADP-ribose Inhibits Arrhythmogenic Oscillations of Intracellular Ca2+ In Heart Cells

“…We have reported previously that, in guinea pig ventricular myocytes stimulated to fire action potentials at 1 Hz, injection of 8-amino-cADPR reduces the Ca 2ϩ transient and accompanying contraction by a mechanism involving a decrease in the quantity of Ca 2ϩ released from the SR but with no reduction in the amount of stored Ca 2ϩ (13). Similarly, application of 8-bromocADPR via a patch pipette has also been shown to suppress the Ca 2ϩ transient and twitch contraction of guinea pig ventricular cells (12). The observations presented here are thus consistent with an action of 8-amino-cADPR and 8-bromo-cADPR to inhibit oscillatory activity induced by isoproterenol or ouabain through the suppression of Ca 2ϩ release from the SR, most likely because of effects (either direct or indirect) on the RyR.…”

“…Studies in intact heart cells have yielded results consistent with a role for endogenous cADPR in the regulation of excitation-contraction coupling. In guinea pig cardiac myocytes stimulated to fire action potentials, Ca 2ϩ transients and contractions are enhanced by intracellular applications of cADPR (12) and reduced by antagonists of cADPR, 8-amino-cADPR and 8-bromo-cADPR (12)(13)(14)(15)(16)(17). These observations are consistent with endogenous cADPR, acting to enhance the Ca 2ϩ sensitivity of CICR, an action that may be antagonized by 8-amino-cADPR and 8-bromo-cADPR.…”

“…8-Bromo-cADPR is another cADPR analogue that has been shown to act as an antagonist of cADPR, albeit with less potency than 8-amino-cADPR (12,14). We therefore investigated the actions of this compound in experiments similar to those presented in Fig.…”

NAADP Controls Cross-talk between Distinct Ca2+ Stores in the Heart

“…We have previously shown that, under control conditions (i.e. absence of any drug in the patch pipette solution), contractions are well maintained over a period of many minutes (34).…”

Peroxynitrite is a positive inotropic agent in atrial and ventricular fibres of the frog heart

“…The guanylyl cyclase is indeed considered as an important target for NO in the heart (Shah, 1996;Kojda & Kottenberg, 1999). In cardiac myocytes, the increase in cGMP levels can co-ordinate the activity of various proteins, including the cGMP-dependent protein kinase, the cGMP-regulated phosphodiesterases (PDE2 and PDE3), and the cationic 'f' current (Iino et al 1997;M ery et al 1997;Musialek et al 1997). In frog fibres, the positive inotropic effect of SIN_1 was unaffected by ODQ (Chesnais et al 1999).…”