Paradoxical SR Ca2+ release in guinea-pig cardiac myocytes after beta-adrenergic stimulation revealed by two-photon photolysis of caged Ca2+.
In heart muscle the amplification and shaping of Ca(2+) signals governing contraction are orchestrated by recruiting a variable number of Ca(2+) sparks. Sparks reflect Ca(2+) release from the sarcoplasmic reticulum (SR) via Ca(2+) release channels (ryanodine receptors, RyRs). RyRs are activated by Ca(2+) influx via L-type Ca(2+) channels with a specific probability that may depend on regulatory mechanisms (e.g. beta-adrenergic stimulation) or diseased states (e.g. heart failure). Changes of RyR phosphorylation may be critical for both regulation and impaired function in disease. Using UV flash photolysis of caged Ca(2+) and short applications of caffeine in guinea-pig ventricular myocytes, we found that Ca(2+) release signals on the cellular level were largely governed by global SR content. During beta-adrenergic stimulation resting myocytes exhibited smaller SR Ca(2+) release signals when activated by photolysis (62.3% of control), resulting from reduced SR Ca(2+) content under these conditions (58.6% of control). In contrast, local signals triggered with diffraction limited two-photon photolysis displayed the opposite behaviour, exhibiting a larger Ca(2+) release (164% of control) despite reduced global and local SR Ca(2+) content. This apparent paradox implies changes of RyR open probabilities after beta-adrenergic stimulation, enhancing local regenerativity and reliability of Ca(2+) signalling. Thus, our results underscore the importance of phosphorylation of RyRs (or of a related protein), as a regulatory physiological mechanism that may also provide new therapeutic avenues to recover impaired Ca(2+) signalling during cardiac disease.
Lindegger
Nicolas
N
Department of Physiology, University of Bern, 3012 Bern, Switzerland.
Niggli
Ernst
E
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D006168:Guinea Pigs; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010782:Photolysis; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D014466:Ultraviolet Rays
D000318:Adrenergic beta-Agonists; D020746:Calcium Channels, L-Type; D010726:Phosphodiesterase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D007545:Isoproterenol; D002118:Calcium