Aging impairs the clustering and reduces the activity of the L-type calcium channels in the heart's pacemaker

Abstract

Every heartbeat is initiated by a spontaneous electrical signal generated inside the cardiac pacemaker. In mammals, including humans, aging leads to the slowdown of the pacemaker rate, which can lead to pathological dysfunction and death. However, the mechanisms behind the age-associated slowdown of the pacemaker are not well understood. The automaticity of the pacemaker relies on a finely tuned balance of ionic currents, where L-type calcium channels play a central role. CaV1.2 and CaV1.3 channels are key players involved in the diastolic depolarization phase and action potential upstroke. In this project, we studied the effects of aging on CaV1.2 and CaV1.3 calcium channel function and regulation. Here we recorded the pacemaker activity and calcium currents on isolated spindle pacemaker cells with patch clamp. The clustering of LTCC has been highlighted with Super-resolution microscopy (GSD). We found that in mouse pacemaker cells, aging causes a reduction of calcium entry through L-type calcium channels, which is not accompanied by a reduction of protein expression. In turn, we found that aging disrupts calcium channel function at different levels. First, aging reduces the expression of L-type calcium channels at the plasma membrane. Second, aging reduces the clustering and nano-organization of L-type calcium channels. And finally, aging reduces the open channel probability, a sign of decreased functional coupling. Moreover, aging also alters the association between L-type calcium channels and beta-adrenergic receptors, altering the adrenergic modulation of the pacemaker cells. Next, we tested the hypothesis that reduced open probability of L-type calcium channels was responsible for a slower firing frequency. Interestingly, we found that the application of BayK was enough to restore intrinsic pacemaker rates in old cells to those levels observed in young cells. Overall, our findings provide evidence that the proper organization and function of L-type calcium channels is affected by aging and that this dysfunction contributes to the slowdown of pacemaker cells in old animals.