Author:
Altamirano Julio,Bers Donald M.
Abstract
Ca2+ current ( ICa) recovery from inactivation is necessary for normal cardiac excitation-contraction coupling. In normal hearts, increased stimulation frequency increases force, but in heart failure (HF) this force-frequency relationship (FFR) is often flattened or reversed. Although reduced sarcoplasmic reticulum Ca2+-ATPase function may be involved, decreased ICa availability may also contribute. Longer action potential duration (APD), slower intracellular Ca2+ concentration ([Ca2+]i) decline, and higher diastolic [Ca2+]i in HF could all slow ICa recovery from inactivation, thereby decreasing ICa availability. We measured the effect of different diastolic [Ca2+]i on ICa inactivation and recovery from inactivation in rabbit cardiac myocytes. Both ICa and Ba2+ current ( IBa) were measured. ICa decay was accelerated only at high diastolic [Ca2+]i (600 nM). IBa inactivation was slower but insensitive to [Ca2+]i. Membrane potential dependence of ICa or IBa availability was not affected by [Ca2+]i <600 nM. Recovery from inactivation was slowed by both depolarization and high [Ca2+]i. We also used perforated patch with action potential (AP)-clamp and normal Ca2+ transients, using various APDs as conditioning pulses for different frequencies (and to simulate HF APD). Recovery of ICa following longer APD was increasingly incomplete, decreasing ICa availability. Trains of long APs caused a larger ICa decrease than short APD at the same frequency. This effect on ICa availability was exacerbated by slowing twitch [Ca2+]i decline by ∼50%. We conclude that long APD and slower [Ca2+]i decline lead to cumulative inactivation limiting ICa at high heart rates and might contribute to the negative FFR in HF, independent of altered Ca2+ channel properties.
Publisher
American Physiological Society
Subject
Physiology (medical),Cardiology and Cardiovascular Medicine,Physiology
Cited by
21 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献