{"doi":"10.17615/fhf1-hs84","title":"Characterization and localization of two ion-binding sites within the pore of cardiac L-type calcium channels","abstract":"L-type Ca channels from porcine cardiac sarcolemma were incorporated into planar lipid bilayers. We characterized interactions of permeant and blocking ions with the channel's pore by (a) studying the current- voltage relationships for Ca2+ and Na+ when equal concentrations of the ions were present in both internal and external solutions, (b) testing the dose-dependent block of Ba2+ currents through the channels by internally applied cadmium, and (c) examining the dose and voltage dependence of the block of Na+ currents through the channels by internally and externally applied Ca2+. We found that the I-V relationship for Na+ appears symmetrical through the origin when equal concentrations of Na+ are present on both sides of the channel (gamma = 90 pS in 200 mM NaCl). The conductance for outward Ca2+ currents with 100 mM Ca2+ on both sides of the channel is approximately 8 pS, a value identical to that observed for inward currents when 100 mM Ca2+ was present outside only. This provides evidence that ions pass through the channel equally well regardless of the direction of net flux. In addition, we find that internal Cd2+ is as effective as external Cd2+ in blocking Ba2+ currents through the channels, again suggesting identical interactions of ions with each end of the pore. Finally, we find that micromolar Ca2+, either in the internal or in the external solution, blocks Na+ currents through the channels. The affinity for internally applied Ca2+ appears the same as that for externally applied Ca2+. The voltage dependence of the Ca(2+)-block suggests that the sites to which Ca2+ binds are located approximately 15% and approximately 85% of the electric field into the pore. Taken together, these data provide direct experimental evidence for the existence of at least two ion binding sites with high affinity for Ca2+, and support the idea that the sites are symmetrically located within the electric field across L-type Ca channels.","journal":"UNC Libraries","year":2021,"id":230660,"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":0.9517,"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":547488,"name":"Robert L. Rosenberg","orcid":null,"position":1,"is_corresponding":false},{"id":837105,"name":"Xiaohua Chen","orcid":"0000-0002-5696-8315","position":0,"is_corresponding":true}],"reference_count":0,"raw_metadata":null,"created_at":"2026-07-18T23:55:09.211909Z","pmid":null,"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":[]}