期刊
CIRCULATION RESEARCH
卷 92, 期 5, 页码 532-538出版社
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1161/01.RES.0000064175.70693.EC
关键词
Ca2+ channels; Ca2+ sparks; excitation-contraction coupling; Ca2+ triggers; trigger clusters
资金
- NHLBI NIH HHS [HL62690, HL52338] Funding Source: Medline
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 ( approximate to 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.
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