Spontaneous and voltage-activated Ca2+ release in adult mouse skeletal muscle fibres expressing the type 3 ryanodine receptor.
The physiological properties and role of the type 3 ryanodine receptor (RyR3), a calcium release channel expressed in a wide variety of cell types, remain mysterious. We forced, in vivo, the expression of RyR3 in adult mouse skeletal muscle fibres using a GFP-RyR3 DNA construct. GFP fluorescence was found within spatially restricted regions of muscle fibres where it exhibited a sarcomere-related banded pattern consistent with a localization within or near the junctional sarcoplasmic reticulum membrane. Immunostaining confirmed the presence of RyR3 together with RyR1 within the GFP-positive areas. In approximately 90% of RyR3-positive fibres microinjected with the calcium indicator fluo-3, we detected repetitive spontaneous transient elevations of intracellular Ca2+ that persisted when fibres were voltage-clamped at -80 mV. These Ca2+ transients remained essentially confined to the RyR3 expression region. They ranged from wide local events to propagating Ca2+ waves and were in some cases associated with local contractile activity. When voltage-clamp depolarizations were applied while fluo-3 or rhod-2 fluorescence was measured within the RyR3-expressing region, no voltage-evoked 'spark-like' elementary Ca2+ release event could be detected. Still global voltage-activated Ca2+ release exhibited a prominent early peak within the RyR3-expressing regions. Measurements were also taken from muscles fibres expressing a GFP-RyR1 construct; positive fibres also yielded a local banded pattern of GFP fluorescence but exhibited no spontaneous Ca2+ release. Results demonstrate that RyR3 is a very potent source of voltage-independent Ca2+ release activity. Conversely we find no evidence that it could contribute to the production of discrete voltage-activated Ca2+ release events in differentiated mammalian skeletal muscle.
Legrand
Claude
C
Physiologie Intégrative Cellulaire et Moléculaire, Université Lyon 1, UMR CNRS 5123, Villeurbanne, France.
Giacomello
Emiliana
E
Berthier
Christine
C
Allard
Bruno
B
Sorrentino
Vincenzo
V
Jacquemond
Vincent
V
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D004594:Electrophysiology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014162:Transfection
D019837:Ryanodine Receptor Calcium Release Channel; D049452:Green Fluorescent Proteins; D002118:Calcium