Cytosolic and Ca depletion signals from j-SR and nj-SR. (A) [Ca]_i and [Ca]_SR changes elicited by AP depolarization from subsarcolemmal (SS) j-SR and central (CT) nj-SR in an atrial myocyte (inset). (B) Mean cytosolic CaT and SR Ca depletion amplitudes of AP-induced Ca release from j-SR and nj-SR. *, P < 0.001. (C) Cytosolic CaT and SR Ca depletion amplitudes along a transverse line showing Ca signals in the SS and transition zone (TZ) between j-SR and nj-SR regions, as well as from CT nj-SR release sites at increasing cell depth (CT₁…CT₆). Distance between measurements is 1 µm. (D) Averaged confocal lines scan images (F/F₀) of Ca sparks and corresponding Ca blinks originating from SS j-SR and CT nj-SR. (E) Mean Ca spark and blink profiles (F/F₀) from images in D. Reproduced from Maxwell and Blatter (2017).