Alterations of L-Type Calcium Current and Cardiac Function in CaMKIIδ Knockout Mice

Abstract

Rationale-Recent studies have highlighted important roles of CaMKII in regulating Ca 2+ handling and excitation-contraction coupling. However, the cardiac effect of chronic CaMKII inhibition has not been well understood.Objective-We have tested the alterations of L-type calcium current (I Ca ) and cardiac function in CaMKIIδ knockout (KO) mouse left ventricle (LV).Methods and Results-We used patch clamp method to record I Ca in ventricular myocytes and found that in KO LV, basal I Ca was significantly increased without changing the transmural gradient of I Ca distribution. Substitution of Ba 2+ for Ca 2+ showed similar increase in I Ba . There was no change in the voltage dependence of I Ca activation and inactivation. I Ca recovery from inactivation, however, was significantly slowed. In KO LV, the Ca 2+ -dependent I Ca facilitation (CDF) and I Ca response to isoproterenol (ISO) were significantly reduced. However, ISO response was reversed by β2-adrenergic receptor (AR) inhibition. Western blots showed a decrease in β1-AR and an increase in Ca v 1.2, β2-AR and Gαi3 protein levels. Ca 2+ transient and sarcomere shortening in KO myocytes were unchanged at 1Hz but reduced at 3Hz stimulation. Echocardiography in conscious mice revealed an increased basal contractility in KO mice. However, cardiac reserve to workload and β-adrenergic stimulation was reduced. Surprisingly, KO mice showed a reduced heart rate in response to workload or β-adrenergic stimulation.Conclusions-Our results implicate physiologic CaMKII activity in maintaining normal I Ca , Ca 2+ handling, excitation-contraction coupling and the in vivo heart function in response to cardiac stress.

Facilitation and Ca2+-dependent Inactivation Are Modified by Mutation of the Cav1.2 Channel IQ Motif

“…3, A-C). As suggested previously (9,17,20,21), facilitation depended on CaMKII. Inhibition of CaMKII activity by KN-93 (1 M) abolished facilitation in CMs from Ctr mice but had no effect in CMs from I/E mice, supporting a specific effect of KN-93 in Ctr CMs (Fig.…”

“…Inhibition of CaMKII by inhibitory peptides or blockers such as KN-93 prolongs recovery from inactivation (10,30), shifts the steady-state inactivation curve to more negative voltages (10,31), and reduces facilitation of I Ca (17,28,30). In addition, knock-out of CaMKII␦ slows down recovery from inactivation and reduces facilitation of I Ca (9). The I/E mutation of the Ca v 1.2 channel likewise prolonged recovery from inactivation, shifted the steady-state inactivation curve to more negative voltages, and reduced facilitation of I Ca .…”

“…A further reason may be the missing facilitation due to the absence of CaMKII-mediated regulation of I Ca , which may reduce the ability of heart muscle to adapt to exercise. Indeed, mice deficient in CaMKII␦ show a reduced heart rate in response to work load or ␤-adrenergic stimulation (9). This phenotype, together with a fully inactivated I Ca , may limit Ca 2ϩ entry and thus Ca 2ϩ -induced Ca 2ϩ release, leading to an insufficient contraction and finally to death of the mice.…”

MicroRNAs Are Essential for Stretch-induced Vascular Smooth Muscle Contractile Differentiation via MicroRNA (miR)-145-dependent Expression of L-type Calcium Channels

“…Expression of L-type calcium channels has been suggested to be repressed by CamKII␦ in cardiomyocytes (35,41). CamKII␦ is regulated by calcium/calmodulin, and findings in smooth muscle have demonstrated a calcium dependence in the long term control of calcium current (42).…”

Mutation of the Calmodulin Binding Motif IQ of the L-type Cav1.2 Ca2+ Channel to EQ Induces Dilated Cardiomyopathy and Death

“…The physiological role of CDF is not entirely clear, but it may serve to offset partly reduced Ca 2ϩ channel availability at high heart rates (8,9). Both types of regulation involve direct binding of the Ca 2ϩ sensor protein calmodulin (CaM) to the Ca v 1.2 channel (7, 10 -12) and activation of Ca 2ϩ /CaM-activated protein kinase II (CaMKII) (8,11,(13)(14)(15)(16).…”