title: Alternative splicing modulates diltiazem sensitivity of cardiac and vascular smooth muscle Ca(v)1.2 calcium channels.
abstract: OBJECTIVE
  As a calcium channel blocker, diltiazem acts mainly on the voltage-gated calcium channels, Ca(v)1.2, for its beneficial effects in cardiovascular diseases such as hypertension, angina and/or supraventricular arrhythmias. However, the effects of diltiazem on different isoforms of Ca(v)1.2 channels expressed in heart and vascular smooth muscles remain to be investigated. Here, we characterized the effects of diltiazem on the splice variants of Ca(v)1.2 channels, predominant in cardiac and vascular smooth muscles.
  
  
  METHODS
  Cardiac and smooth muscle isoforms of Ca(v)1.2 channels were expressed in human embryonic kidney cells and their electrophysiological properties were characterized using whole-cell patch-clamp techniques.
  
  
  RESULTS
  Under closed-channel and use-dependent block (0.03 Hz), cardiac splice variant Ca(v)1.2CM was less sensitive to diltiazem than two major smooth muscle splice variants, Ca(v)1.2SM and Ca(v)1.2b. Ca(v)1.2CM has a more positive half-inactivation potential than the smooth muscle channels, and diltiazem shifted it less to negative potential. Additionally, the current decay was slower in Ca(v)1.2CM channels. When we modified alternatively spliced exons of cardiac Ca(v)1.2CM channels into smooth muscle exons, we found that all three loci contribute to the different diltiazem sensitivity between cardiac and smooth muscle splice isoforms.
  
  
  CONCLUSIONS
  Alternative splicing of Ca(v)1.2 channels modifies diltiazem sensitivity in the heart and blood vessels. Gating properties altered by diltiazem are different in the three channels.
authors.affiliation: Department of Cardiology, West China School of Medicine, Sichuan University, Chengdu, China.
authors.forename: Heng Yu
authors.initials: HY
authors.lastname: Zhang
authors.forename: Ping
authors.initials: P
authors.lastname: Liao
authors.forename: Jue Jin
authors.initials: JJ
authors.lastname: Wang
authors.forename: De Jie
authors.initials: DJ
authors.lastname: Yu
authors.forename: Tuck Wah
authors.initials: TW
authors.lastname: Soong
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D004110:Diltiazem / Q000494:pharmacology*; D006801:Humans; D008969:Molecular Sequence Data; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; C419385:L-type calcium channel alpha(1C); D004110:Diltiazem