Enhanced resistance to permeability transition in interfibrillar cardiac mitochondria in dogs: effects of aging and long-term aldosterone infusion

Abstract

Functional differences between subsarcolemmal and interfibrillar cardiac mitochondria (SSM and IFM) have been observed with aging and pathological conditions in rodents. Results are contradictory, and there is little information from large animal models. We assessed the respiratory function and resistance to mitochondrial permeability transition (MPT) in SSM and IFM from healthy young (1 yr) and old (8 yr) female beagles and in old beagles with hypertension and left ventricular (LV) wall thickening induced by 16 wk of aldosterone infusion. MPT was assessed in SSM and IFM by Ca(2+) retention and swelling. Healthy young and old beagles had similar mitochondrial structure, respiratory function, and Ca(2+)-induced MPT within SSM and IFM subpopulations. On the other hand, oxidative capacity and resistance to Ca(2+)-induced MPT were significantly greater in IFM compared with SSM in all groups. Old beagles treated with aldosterone had greater LV wall thickness and worse diastolic filling but normal LV chamber volume and systolic function. Treatment with aldosterone did not alter mitochondrial respiratory function but accelerated Ca(2+)-induced MPT in SSM, but not IFM, compared with healthy old and young beagles. In conclusion, in a large animal model, oxidative capacity and resistance to MPT were greater in IFM than in SSM. Furthermore, aldosterone infusion increased susceptibility to MPT in SSM, but not IFM. Together this suggests that SSM are less resilient to acute stress than IFM in the healthy heart and are more susceptible to the development of pathology with chronic stress.

Fig. 1.

Time course of arterial blood pressure in the old dogs treated with aldosterone. *P < 0.05 compared with baseline; †P < 0.01 compared with baseline.

Fig. 2.

Echocardiographic assessment of left ventricular (LV) function in the old dogs treated with aldosterone (Aldo). Measurements were made before treatment and after 15 wk of aldosterone infusion. EDD, end-diastolic diameter; E/A, peak rapid filling velocity (E)-to-peak atrial filling velocity (A) ratio; NS, not significant.

Fig. 3.

LV mitochondrial yield and flow cytometry results. Δψm, mitochondrial membrane potential; JC-1, 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazol carbocyanine iodide; Prot, protein. *P < 0.05, interfibrillar cardiac mitochondria (IFM) compared with subsarcolemmal cardiac mitochondria (SSM); †P < 0.05 compared with Old within given mitochondrial subpopulation; #P < 0.05 compared with Young within given mitochondrial subpopulation.

Fig. 4.

Right ventricular (RV) mitochondrial yield and flow cytometry results. *P < 0.05, IFM compared with SSM; †P < 0.05 compared with Old within given mitochondrial subpopulation; #P < 0.05 compared with Young within given mitochondrial subpopulation.

Fig. 5.

LV mitochondrial state-3 respiration in SSM (white bars) and IFM (black bars) (left) and the respiratory control ratio (state 3/state 4 without oligomycin) (right). *P < 0.05 IFM compared with SSM.

Fig. 6.

RV mitochondrial state-3 respiration in SSM (white bars) and IFM (black bars) (left) and the respiratory control ratio (state 3/state 4 without oligomycin) (right). *P < 0.05, IFM compared with SSM; #P < 0.05 compared with Young within given mitochondrial subpopulation.

Fig. 7.

LV mitochondrial state-4 respiration in SSM (white bars) and IFM (black bars) without oligomycin (left) and with oligomycin to inhibit ATP production by complex V. *P < 0.05, IFM compared with SSM; †P < 0.05 compared with Old.

Fig. 8.

RV mitochondrial state-4 respiration in SSM (white bars) and IFM (black bars) without oligomycin (left) and with oligomycin to inhibit ATP production by complex V. *P < 0.05, IFM compared with SSM; †P < 0.05 compared with Old within given mitochondrial subpopulation; #P < 0.05 compared with Young within given mitochondrial subpopulation.

Fig. 9.

Baseline absorbance at 540 nm of LV mitochondria without addition of Ca²⁺. *P < 0.05, IFM compared with SSM; †P < 0.05 compared with Old; #P < 0.05 compared with Young.

Fig. 10.

Change in absorbance at 540 nm, index of LV mitochondrial swelling, following addition of either 0.5 or 1.0 μmol Ca²⁺/mg mitochondrial protein. AU, arbitrary units. *P < 0.05, IFM compared with SSM.

Fig. 11.

Comparison between IFM and SSM from the LV for each group of dogs for extramitochondrial Ca²⁺ concentration plotted as a function of the cumulative Ca²⁺ load. Mito Prot, mitochondrial protein. *P < 0.05, IFM compared with SSM.

Fig. 12.

Extramitochondrial Ca²⁺ concentration plotted as a function of cumulative Ca²⁺ load for SSM (top) and IFM (bottom) from the LV. *P < 0.05 compared with Young; †P < 0.05 compared with Old.