AJP - Heart Calcium Transients and Cell-Sarcomere
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Am J Physiol Heart Circ Physiol 279: H1482-H1489, 2000;
0363-6135/00 $5.00
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Vol. 279, Issue 4, H1482-H1489, October 2000

cADP ribose and [Ca2+]i regulation in rat cardiac myocytes

Y. S. Prakash1, Mathur S. Kannan2, Timothy F. Walseth3, and Gary C. Sieck1,4

Departments of 1 Anesthesiology and of 4 Physiology and Biophysics, Mayo Foundation, Rochester 55905; and Departments of 2 Veterinary Pathobiology and 3 Pharmacology, University of Minnesota, St. Paul, Minnesota 55108

cADP ribose (cADPR)-induced intracellular Ca2+ concentration ([Ca2+]i) responses were assessed in acutely dissociated adult rat ventricular myocytes using real-time confocal microscopy. In quiescent single myocytes, injection of cADPR (0.1-10 µM) induced sustained, concentration-dependent [Ca2+]i responses ranging from 50 to 500 nM, which were completely inhibited by 20 µM 8-amino-cADPR, a specific blocker of the cADPR receptor. In myocytes displaying spontaneous [Ca2+]i waves, increasing concentrations of cADPR increased wave frequency up to ~250% of control. In electrically paced myocytes (0.5 Hz, 5-ms duration), cADPR increased the amplitude of [Ca2+]i transients in a concentration-dependent fashion, up to 150% of control. Administration of 8-amino-cADPR inhibited both spontaneous waves as well as [Ca2+]i responses to electrical stimulation, even in the absence of exogenous cADPR. However, subsequent [Ca2+]i responses to 5 mM caffeine were only partially inhibited by 8-amino-cADPR. In contrast, even under conditions where ryanodine receptor (RyR) channels were blocked with ryanodine, high cADPR concentrations still induced an [Ca2+]i response. These results indicate that in cardiac myocytes, cADPR induces Ca2+ release from the sarcoplasmic reticulum through both RyR channels and via mechanisms independent of RyR channels.

heart; ryanodine receptor; second messenger; confocal microscopy; sarcoplasmic reticulum; intracellular calcium concentration


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