Ca2+ sparks in rabbit ventricular myocytes evoked by action potentials: involvement of clusters of L-type Ca2+ channels.
It is not clear how many L-type Ca2+ channels (LCCs) are required to ensure that a Ca2+ spark is triggered during a normal mammalian action potential (AP). We investigated this in rabbit ventricular myocytes by examining both the properties of sparks evoked by APs and the activity of LCCs. We measured Ca2+ sparks evoked by repeated APs with pipettes containing 2 mmol/L EGTA and single LCC activity in cell-attached patches depolarized to +50 mV using pipettes containing 110 mmol/L Ba2+. With 2 mmol/L Ca2+ in the external solution, we observed sparks at the beginning of every evoked AP at numerous locations. Each spark was observed repeatedly at a fixed location and began during a limited interval after the AP peak. These sparks occurred with a probability of approximately unity. However, the chance that an LCC does not open during the interval when a spark is triggered is quite high ( approximately 0.13). Therefore, because single channels open with a probability significantly lower than 1, more than one LCC must be available to ensure that sparks are triggered with a probability of approximately unity. We conclude that it is likely that a cluster of LCCs is involved in gating a cluster of ryanodine receptors at the beginning of an AP.
Inoue
Masashi
M
Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East Back, Salt Lake City, Utah 84112-5000, USA. inoue@cvrti.utah.edu
Bridge
John H B
JH
D000200:Action Potentials; D000818:Animals; D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002478:Cells, Cultured; D004553:Electric Conductivity; D005071:Evoked Potentials; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D017136:Ion Transport; D007700:Kinetics; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D016276:Ventricular Function
D020746:Calcium Channels, L-Type; D001464:Barium; D002118:Calcium