Unitary Ca2+ current through mammalian cardiac and amphibian skeletal muscle ryanodine receptor Channels under near-physiological ionic conditions.
Ryanodine receptor (RyR) channels from mammalian cardiac and amphibian skeletal muscle were incorporated into planar lipid bilayers. Unitary Ca2+ currents in the SR lumen-to-cytosol direction were recorded at 0 mV in the presence of caffeine (to minimize gating fluctuations). Currents measured with 20 mM lumenal Ca2+ as exclusive charge carrier were 4.00 and 4.07 pA, respectively, and not significantly different. Currents recorded at 1-30 mM lumenal Ca2+ concentrations were attenuated by physiological [K+] (150 mM) and [Mg2+] (1 mM), in the same proportion (approximately 55%) in mammalian and amphibian channels. Two amplitudes, differing by approximately 35%, were found in amphibian channel studies, probably corresponding to alpha and beta RyR isoforms. In physiological [Mg2+], [K+], and lumenal [Ca2+] (1 mM), the Ca2+ current was just less than 0.5 pA. Comparison of this value with the Ca2+ flux underlying Ca2+ sparks suggests that sparks in mammalian cardiac and amphibian skeletal muscles are generated by opening of multiple RyR channels. Further, symmetric high concentrations of Mg2+ substantially reduced the current carried by 10 mM Ca2+ (approximately 40% at 10 mM Mg2+), suggesting that high Mg2+ may make sparks smaller by both inhibiting RyR gating and reducing unitary current.
Kettlun
Claudia
C
Department of Physiology, Loyola University Chicago, 2160 S. First Ave., Maywood, IL 60153, USA.
González
Adom
A
Ríos
Eduardo
E
Fill
Michael
M
D000465:Algorithms; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008051:Lipid Bilayers; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D011894:Rana pipiens; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D013552:Swine
D015220:Calcium Channels; D008051:Lipid Bilayers; D010726:Phosphodiesterase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D008274:Magnesium; D011188:Potassium