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Войти в исследования Cardiovascular research · 2006
Shock-induced changes of Ca(i)2+ and Vm in myocyte cultures and computer model: Dependence on the timing of shock application.
СтатьяПоддержка NIH: внешняя программаПоддержка исследования: вне правительства СШАНазвание и аннотация: Перевод в очереди
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Raman Vidya, Pollard Andrew E, Fast Vladimir G
Аннотация
OBJECTIVES: Responses of Ca(i)2+ to electrical shocks are believed to be important in defibrillation but measurements of shock-induced Ca(i)2+ changes during different phases of the action potential (AP) are lacking. The effects of shocks on Ca(i)2+ and Vm were investigated in geometrically defined cell cultures and in a computer model.
METHODS: Uniform-field shocks (E = 10.4+/-0.9 V/cm) were applied 15-300 ms after AP upstroke in strands of cultured neonatal rat myocytes. Optical mapping was used to measure shock-induced Ca(i)2+ and Vm changes. A rat ionic model was used to elucidate ionic mechanisms of Ca(i)2+ responses.
RESULTS: In experiments and simulations, shocks applied with short delays (15-40 ms) caused a transient decrease of Ca(i)2+ at sites of both DeltaV(+)m and DeltaV(-)m. Simulations indicated that the Ca(i)2+ decrease at DeltaV(+)m sites was caused by reversed outward flow of L-type Ca2+ current (I(CaL)), while the Ca(i)2+ decrease at DeltaV(-)m sites was due to the NaCa exchanger (NCX). At intermediate delays (40-150 ms), shocks caused a Ca(i)2+ decrease at sites of DeltaV(-)m and an increase at sites of DeltaV(+)m. Simulations indicated that the Ca(i)2+ increase at DeltaV(+)m sites was caused by transient reactivation of I(CaL) combined with a reverse-mode operation of NCX. Shocks applied at long delays (150-300 ms) caused a Ca(i)2+ increase at DeltaV(+)m and no change at DeltaV(-)m sites.
CONCLUSION: Effects of shocks on Ca(i)2+ depend on the timing of shock application. Shocks applied during the early AP cause a transient Ca(i)2+ decrease, while later in AP shocks induce a Ca(i)2+ increase at sites of DeltaV(+)m. Shock-induced Ca(i)2+ changes in different AP phases are primarily determined by combination of I(CaL) and NCX.
METHODS: Uniform-field shocks (E = 10.4+/-0.9 V/cm) were applied 15-300 ms after AP upstroke in strands of cultured neonatal rat myocytes. Optical mapping was used to measure shock-induced Ca(i)2+ and Vm changes. A rat ionic model was used to elucidate ionic mechanisms of Ca(i)2+ responses.
RESULTS: In experiments and simulations, shocks applied with short delays (15-40 ms) caused a transient decrease of Ca(i)2+ at sites of both DeltaV(+)m and DeltaV(-)m. Simulations indicated that the Ca(i)2+ decrease at DeltaV(+)m sites was caused by reversed outward flow of L-type Ca2+ current (I(CaL)), while the Ca(i)2+ decrease at DeltaV(-)m sites was due to the NaCa exchanger (NCX). At intermediate delays (40-150 ms), shocks caused a Ca(i)2+ decrease at sites of DeltaV(-)m and an increase at sites of DeltaV(+)m. Simulations indicated that the Ca(i)2+ increase at DeltaV(+)m sites was caused by transient reactivation of I(CaL) combined with a reverse-mode operation of NCX. Shocks applied at long delays (150-300 ms) caused a Ca(i)2+ increase at DeltaV(+)m and no change at DeltaV(-)m sites.
CONCLUSION: Effects of shocks on Ca(i)2+ depend on the timing of shock application. Shocks applied during the early AP cause a transient Ca(i)2+ decrease, while later in AP shocks induce a Ca(i)2+ increase at sites of DeltaV(+)m. Shock-induced Ca(i)2+ changes in different AP phases are primarily determined by combination of I(CaL) and NCX.