Sarco/endoplasmic reticulum calcium ATPase activity is unchanged despite increased myofilament calcium sensitivity in Zucker type 2 diabetic fatty rat heart

Abstract

Systolic and diastolic dysfunction in diabetes have frequently been associated with abnormal calcium (Ca2+) regulation. However, there is emerging evidence that Ca2+ mishandling alone is insufficient to fully explain diabetic heart dysfunction, with focus shifting to the properties of the myofilament proteins. Our aim was to examine the effects of diabetes on myofilament Ca2+ sensitivity and Ca2+ handling in left ventricular tissues isolated from the same type 2 diabetic rat hearts. We measured the force-pCa relationship in skinned left ventricular cardiomyocytes isolated from 20-week-old type 2 diabetic and non-diabetic rats. Myofilament Ca2+ sensitivity was greater in the diabetic relative to non-diabetic cardiomyocytes, and this corresponded with lower phosphorylation of cardiac troponin I (cTnI) at ser23/24 in the diabetic left ventricular tissues. Protein expression of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), phosphorylation of phospholamban (PLB) at Ser16, and SERCA/PLB ratio were lower in the diabetic left ventricular tissues. However, the maximum SERCA Ca2+ uptake rate was not different between the diabetic and non-diabetic myocardium. Our data suggest that impaired contractility in the diabetic heart is not caused by SERCA Ca2+ mishandling. This study highlights the important role of the cardiac myofilament and provides new insight on the pathophysiology of diabetic heart dysfunction.

The carbon monoxide prodrug oCOm‐21 increases Ca2+ sensitivity of the cardiac myofilament

“…Our group (Greenman et al., 2021 ; Ng et al., 2022 ) and others (Budde et al., 2021 ; Sevrieva et al., 2023 ; van der Velden et al., 2003 ) have shown that phosphorylation of myofilament proteins (including cTnI and myosin binding protein C) is associated with changes in Ca 2+ sensitivity. CO activates the soluble guanylate cyclase (sGC) pathway to phosphorylate cytosolic (e.g., L‐type Ca 2+ channel, ryanodine receptor) and myofilament proteins such as TnI at Ser23/24 (Layland et al., 2002 ; Stone & Marletta, 1994 ).…”

“…Permeabilized LV cardiomyocytes isolated from male Sprague Dawley rats were used to examine changes in Ca 2+ sensitivity as described previously (Greenman et al., 2022 ; Ng et al., 2022 ). Briefly, frozen LV tissue was homogenized in a Relax buffer (100 mM KCl, 1.75 mM EGTA, 10 mM imidazole, 4 mM ATP, 5 mM MgCl 2 , pH 7) with HALT protease and phosphatase inhibitor cocktail.…”

Regulation of Prepro-NeuropeptideW/B and Its Receptor in the Heart of ZDF Rats: An Animal Model of Type II DM

“…The diminished calcium transient did not cause a significant change in the amplitude of sarcomeric contraction in diabetic cardiomyocytes which followed previous findings in ZDF rats [ 30 , 31 ]. A possible explanation could be provided by an increased myofilament calcium sensitivity serving as a compensatory mechanism in ZDF rats [ 32 ]. NPB in vitro application positively affected calcium transients from both animal groups with no effect on the contractility.…”