{"doi":"10.3389/fphys.2021.725798","title":"Acute Detubulation of Ventricular Myocytes Amplifies the Inhibitory Effect of Cholinergic Agonist on Intracellular Ca2+ Transients","abstract":"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 Ca 2+ handling by muscarinic receptors is not well-defined. Using confocal Ca 2+ imaging, patch-clamp techniques, and immunocytochemistry, the relationship between t-tubule density and cholinergic regulation of intracellular Ca 2+ 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 Ca 2+ 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 Ca 2+ -sensitive dye, was used to classify image pixels into the regions functionally coupled or uncoupled to the sarcolemmal Ca 2+ influx (I Ca ). CCh decreased the fraction of coupled regions and suppressed Ca 2+ propagation from sarcolemma inside the cell. Formamide treatment reduced I Ca density and decreased sarcoplasmic reticulum (SR) Ca 2+ content. CCh did not change SR Ca 2+ content in Iso-stimulated control and formamide-treated myocytes. CCh inhibited peak I Ca recorded in the presence of Iso by ∼20% in both the control and detubulated myocytes. Reducing I Ca amplitude up to 40% by changing the voltage step levels from 0 to –25 mV decreased Ca 2+ 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 Ca 2+ 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 Ca 2+ release and propagation to muscarinic receptor-mediated inhibition of both I Ca and CaMKII activity.","journal":"Frontiers in Physiology","year":2021,"id":226437,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":0,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9443,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2021-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":693595,"name":"Vladimir Bogdanov","orcid":"0000-0001-9287-5303","position":1,"is_corresponding":false},{"id":271059,"name":"Dmitry Terentyev","orcid":"0000-0002-9530-7384","position":2,"is_corresponding":false},{"id":271057,"name":"Sándor Györke","orcid":"0000-0002-0821-1983","position":3,"is_corresponding":false},{"id":271058,"name":"Andriy E. Belevych","orcid":"0000-0002-1272-5784","position":0,"is_corresponding":true}],"reference_count":47,"raw_metadata":null,"created_at":"2026-07-18T23:54:34.185847Z","pmid":"34512394","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}