Figure 1:

Mitochondria can influence Ca²⁺ transients of cardiomyocytes. The cartoon depicts different mechanisms by which mitochondria respond to altered cytosolic Ca²⁺levels. A) Mitochondria take up Ca²⁺ from store operated Ca²⁺ channels and prevent Ca²⁺ dependent inactivation of the channel. B) Mitochondria can serve as a firewall to prevent global increases in Ca²⁺. In atrial cardiomyocytes, Ca²⁺ entry across the sarcolemma (via cav1.2) is loaded into mitochondria that are present underneath the surface membrane. The amplitude of the Ca²⁺ transients becomes larger when cells are pretreated with agent that depolarize the mitochondrial membrane. C) Nanotunnels are specialized membrane extensions that connect two mitochondria. This phenomenon develops in cardiomyocytes with leaky Ca²⁺ release channels (RYR2). D) Elevated Ca²⁺ levels in the cytosol can trigger morphologic change to mitochondria called fission.