Effects of hindlimb suspension on cytosolic Ca2+ and [3H]ryanodine binding in cardiac myocytes.
Effects of a 14-day hindlimb suspension were examined on [3H]ryanodine binding to rat ventricular microsomes and on cytosolic Ca2+ concentration ([Ca2+]i) and voltage-dependent Ca2+ channels in isolated ventricular myocytes. In suspended rats, the amplitude of the twitch [Ca2+]i transient was increased without significant modifications of the basal [Ca2+]i and sarcoplasmic reticulum content. Because cell capacitance, L-type Ca2+-current density, and Ca2+-channel gating were not significantly modified after suspension, the increase in [Ca2+]i was expected to reside in a change in ryanodine receptors. Scatchard analysis of [3H]ryanodine binding revealed that suspension enhanced binding by increasing the affinity of the receptors for [3H]ryanodine without affecting the maximal binding capacity. Both Ca2+-release channel activity and [3H]ryanodine binding are modulated by Ca2+. However, the Ca2+ sensitivity of [3H]ryanodine binding remained unchanged after suspension. Taken together, these results suggest that the increase in twitch [Ca2+]i transients after suspension may result from a change in the intrinsic properties of the ryanodine receptors but not from a change in the expression level of these receptors.
Halet
G
G
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, Centre Nationale de la Recherche Scientifique Enseignement Supérieur Associé 5017, Université de Bordeaux II, 33076 Bordeaux, France.
Viard
P
P
Morel
J L
JL
Mironneau
J
J
Mironneau
C
C
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D003600:Cytosol / Q000378:metabolism*; D004553:Electric Conductivity; D019417:Hindlimb Suspension; D008297:Male; D008861:Microsomes / Q000378:metabolism; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000378:metabolism*; D014316:Tritium
D014316:Tritium; D012433:Ryanodine; D002118:Calcium