Integration of calcium signals by calmodulin in rat sensory neurons.
We have used the fluorescently labelled calmodulin TA-CaM to follow calmodulin activation during depolarization of adult rat sensory neurons. Calcium concentration was measured simultaneously using the low affinity indicator Oregon Green BAPTA 5N. TA-CaM fluorescence increased during a 200-ms depolarization but then continued to increase during the subsequent 500 ms, even though total cell calcium was falling at this time. In the next few seconds TA-CaM fluorescence fell, but to a new elevated level that was then maintained for several tens of seconds. During a train of depolarizations that evoked a series of largely independent calcium changes TA-CaM fluorescence was in contrast raised for the duration of the train and for many tens of seconds afterwards. The presence of a peptide corresponding to the calmodulin binding domain of myosin light chain kinase significantly increased the depolarization-induced TA-CaM fluorescence increase and slowed the subsequent fall of fluorescence. We interpret the slow recovery component of the TA-CaM signal as reflecting the slow dissociation of calcium--calmodulin--calmodulin binding protein complexes. Our results show that after brief electrical activity calmodulin's interaction with calmodulin binding proteins persists for approximately one minute.
Milikan
Jacob M
JM
Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK.
Carter
Tom D
TD
Horne
John H
JH
Tzortzopoulos
Athanasios
A
Török
Katalin
K
Bolsover
Stephen R
SR
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002147:Calmodulin / Q000031:analogs & derivatives* / Q000378:metabolism*; D005260:Female; D005456:Fluorescent Dyes; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism*; D007093:Imidazoles; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D009475:Neurons, Afferent / Q000166:cytology / Q000378:metabolism*; D009930:Organic Chemicals; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000502:physiology*; D013997:Time Factors; D014227:Triazines
C404210:2-chloro-(6-(4-N,N-diethylaminophenyl)-1,4,5-triazin-4-yl)calmodulin; D001572:Benzofurans; D002147:Calmodulin; D005456:Fluorescent Dyes; D007093:Imidazoles; C403124:Oregon Green BAPTA-dextran; D009930:Organic Chemicals; D010446:Peptide Fragments; D014227:Triazines; C082877:fura red; D002118:Calcium