Fig. 3.

Cardiomyocyte mechanics and expression of calcium regulatory proteins. Isolated cardiac myocyte studies with representative whole cell calcium transients and sarcomeric shortening (A). Akita^ins2 myocytes (dashed) display diastolic dysfunction with increased sarcomeric relaxation and calcium reuptake compared with wild-type (solid); however, peak sarcomeric shortening and peak calcium transient are unchanged between the WT and Akita^ins2. B: representative Western blot analyses of Cav1.2, Na⁺/Ca²⁺ exchanger 1 (NCX1), sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA2a), and phospholamban (PLB) in the Akita^ins2 mouse, with quantitative densitometry. pPLB:PLB and SERCA2a:PLB ratios were decreased to <50% of WT levels. Data shown are means ± SD; n = 5 animals/group. *P < 0.05; **P < 0.01. C: caffeine-induced sarcoplasmic reticulum (SR) Ca²⁺ content in Akita^ins2 compared with WT. SR Ca²⁺ and transient decay rates (NCX forward mode function) were both determined by rapid exposure to 20 mM caffeine in 0 Ca²⁺ and 0 Na⁺ Tyrode buffer, effectively blocking NCX (−NCX, red tracing) and 0 Ca²⁺ and 140 mM Na⁺ to monitor decay rates with functional NCX (+NCX, blue tracing). Time constant of decay (inset) did not show a significant change between the two groups when NCX was active. D: action potential kinetics in cardiomyocytes (CM) from Akita^ins2 and WT measured using di-8-ANEPPS; 10% and 80% APD recovery in the Akita^ins2 was significantly longer than WT controls (*P < 0.05) (n = 4 animals/group; >15 cells/animal).