Calmodulin kinase is functionally targeted to the action potential plateau for regulation of L-type Ca2+ current in rabbit cardiomyocytes.
L-type Ca2+ current (ICa-L) triggers Ca2+ release from the sarcoplasmic reticulum (SR) and both SR and ICa-L are potential sources of intracellular Ca2+ (Ca2+i) for feedback regulation of ICa-L. Ca2+i bound to calmodulin (Ca2+-CaM) can inhibit ICa-L, while Ca2+-CaM can also activate Ca2+-CaM-dependent protein kinase II (CaMK) to increase ICa. However, it is not known whether ICa-L or the SR is the primary source of Ca2+ for ICa-L regulation. The L-type Ca2+ channel C terminus is implicated as a critical transduction element for ICa-L responses to Ca2+-CaM and CaMK, and the C terminus undergoes voltage-dependent steric changes, suggesting that Ca2+i control of ICa-L may also be regulated by cell membrane potential. We developed conditions to separately test the relationship of Ca2+-CaM and CaMK to ICa-L and SR Ca2+i release during voltage clamp conditions modelled upon time and voltage domains relevant to the cardiac action potential. Here we show that CaMK increases ICa-L after brief positive conditioning pulses, whereas Ca2+-CaM reduces ICa-L over a broad range of positive and negative conditioning potentials. SR Ca2+ release was required for both Ca2+-CaM and CaMK ICa-L responses after strongly positive conditioning pulses (+10 and +40 mV), while Ca2+i from ICa-L was sufficient for Ca2+-CaM during weaker depolarizations. These findings show that ICa-L responses to CaMK are voltage dependent and suggest a new model of L-type Ca2+ channel regulation where voltage-dependent changes control ICa-L responses to Ca2+-CaM and CaMK signalling.
Wu
Yuejin
Y
Department of Internal Medicine, Vanderbilt University Medical Center, Nashville, TN 37232-6300, USA.
Kimbrough
John T
JT
Colbran
Roger J
RJ
Anderson
Mark E
ME
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D004558:Electric Stimulation; D051379:Mice; D032383:Myocytes, Cardiac / Q000201:enzymology*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D020746:Calcium Channels, L-Type; D002147:Calmodulin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium