title: Ca(v)1.3 channels produce persistent calcium sparklets, but Ca(v)1.2 channels are responsible for sparklets in mouse arterial smooth muscle.
abstract: Ca(2+) sparklets are local elevations in intracellular Ca(2+) produced by the opening of a single or a cluster of L-type Ca(2+) channels. In arterial myocytes, Ca(2+) sparklets regulate local and global intracellular Ca(2+). At present, the molecular identity of the L-type Ca(2+) channels underlying Ca(2+) sparklets in these cells is undetermined. Here, we tested the hypotheses that voltage-gated calcium channel-alpha 1.3 subunit (Ca(v)1.3) can produce Ca(2+) sparklets and that Ca(v)1.2 and/or Ca(v)1.3 channels are responsible for Ca(2+) sparklets in mouse arterial myocytes. First, we investigated the functional properties of single Ca(v)1.3 channels in tsA201 cells. With 110 mM Ba(2+) as the charge carrier, Ca(v)1.3 channels had a conductance of 20 pS. This value is similar to that of Ca(v)1.2 and native L-type Ca(2+) channels. As previously shown for Ca(v)1.2 channels, Ca(v)1.3 channels can operate in two gating modes characterized by short and long open times. Expressed Ca(v)1.3 channels also produced Ca(2+) sparklets. Ca(v)1.3 sparklets had properties similar to those produced by Ca(v)1.2 and native L-type channels, including quantal amplitude, dihydropyridine sensitivity, bimodal gating, and dual-event duration times. However, the voltage dependencies of conductance and steady-state inactivation of the Ca(2+) current (I(Ca)) in arterial myocytes were similar to those recorded from cells expressing Ca(v)1.2 but not Ca(v)1.3 channels. Furthermore, nifedipine (10 microM) eliminated Ca(2+) sparklets in wild-type myocytes but not in myocytes expressing dihydropyridine-insensitive Ca(v)1.2 channels. Accordingly, Ca(v)1.3 transcript and protein were not detected in isolated arterial myocytes. We conclude that although Ca(v)1.3 channels can produce Ca(2+) sparklets, Ca(v)1.2 channels underlie I(Ca), Ca(2+) sparklets, and hence dihydropyridine-sensitive Ca(2+) influx in mouse arterial myocytes.
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Box 357290, Seattle, WA 98195, USA.
authors.forename: Manuel F
authors.initials: MF
authors.lastname: Navedo
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Amberg
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Westenbroek
authors.forename: Martina J
authors.initials: MJ
authors.lastname: Sinnegger-Brauns
authors.forename: William A
authors.initials: WA
authors.lastname: Catterall
authors.forename: Jörg
authors.initials: J
authors.lastname: Striessnig
authors.forename: Luis F
authors.initials: LF
authors.lastname: Santana
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D004594:Electrophysiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques
chemical_list: C514350:CACNA1C protein, mouse; C485995:Cacna1d protein, mouse; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D009543:Nifedipine; D002118:Calcium