Acute Detubulation of Ventricular Myocytes Amplifies the Inhibitory Effect of Cholinergic Agonist on Intracellular Ca2+ Transients

Frontiers in Physiology

Vladimir Bogdanov¹  Sandor Gyorke¹  Andriy E. Belevych¹  Dmitry A. Terentyev¹ 

[1] Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, OH, United States;Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, United States;

关键词: excitation-contraction coupling;    t-tubule;    muscarinic receptor agonist;    calcium microdomains;    ventricular myocyte;   

DOI  :  10.3389/fphys.2021.725798

来源: DOAJ

【 摘 要 】

Muscarinic receptors expressed in cardiac myocytes play a critical role in the regulation of heart function by the parasympathetic nervous system. How the structural organization of cardiac myocytes affects the regulation of Ca2+ handling by muscarinic receptors is not well-defined. Using confocal Ca2+ imaging, patch-clamp techniques, and immunocytochemistry, the relationship between t-tubule density and cholinergic regulation of intracellular Ca2+ in normal murine ventricular myocytes and myocytes with acute disruption of the t-tubule system caused by formamide treatment was studied. The inhibitory effect of muscarinic receptor agonist carbachol (CCh, 10 μM) on the amplitude of Ca2+ transients, evoked by field-stimulation in the presence of 100 nM isoproterenol (Iso), a β-adrenergic agonist, was directly proportional to the level of myocyte detubulation. The timing of the maximal rate of fluorescence increase of fluo-4, a Ca2+-sensitive dye, was used to classify image pixels into the regions functionally coupled or uncoupled to the sarcolemmal Ca2+ influx (ICa). CCh decreased the fraction of coupled regions and suppressed Ca2+ propagation from sarcolemma inside the cell. Formamide treatment reduced ICa density and decreased sarcoplasmic reticulum (SR) Ca2+ content. CCh did not change SR Ca2+ content in Iso-stimulated control and formamide-treated myocytes. CCh inhibited peak ICa recorded in the presence of Iso by ∼20% in both the control and detubulated myocytes. Reducing ICa amplitude up to 40% by changing the voltage step levels from 0 to –25 mV decreased Ca2+ transients in formamide-treated but not in control myocytes in the presence of Iso. CCh inhibited CaMKII activity, whereas CaMKII inhibition with KN93 mimicked the effect of CCh on Ca2+ transients in formamide-treated myocytes. It was concluded that the downregulation of t-tubules coupled with the diminished efficiency of excitation–contraction coupling, increases the sensitivity of Ca2+ release and propagation to muscarinic receptor-mediated inhibition of both ICa and CaMKII activity.

【 授权许可】

Unknown