title: Ca2+ channel currents and contraction in CaVbeta3-deficient ileum smooth muscle from mouse.
abstract: Voltage activated L-type Ca(2+) channels are the principal Ca(2+) channels in intestinal smooth muscle cells. They comprise the ion conducting Ca(V)1 pore and the ancillary subunits alpha(2)delta and beta. Of the four Ca(V)beta subunits Ca(V)beta(3) is assumed to be the relevant Ca(V)beta protein in smooth muscle. In protein lysates isolated from mouse ileum longitudinal smooth muscle we could identify the Ca(V)1.2, Ca(V)alpha(2), Ca(V)beta(2) and Ca(V)beta(3) proteins, but not the Ca(V)beta(1) and Ca(V)beta(4) proteins. Protein levels of Ca(V)1.2, Ca(V)alpha(2) and Ca(V)beta(2) are not altered in ileum smooth muscle obtained from Ca(V)beta(3)-deficient mice indicating that there is no compensatory increase of the expression of these channel proteins. Neither the Ca(V)beta(2) nor the other Ca(V)beta proteins appear to substitute for the lacking Ca(V)beta(3). L-type Ca(2+) channel properties including current density, inactivation kinetics as well as Cd(2+)- and dihydropyridine sensitivity were identical in cells of both genotypes suggesting that they do not require the presence of a Ca(V)beta(3) protein. However, a key hallmark of the Ca(V)beta modulation of Ca(2+) current, the hyperpolarisation of channel activation is slightly but significantly reduced by 4 mV. In addition to L-type Ca(2+) currents T-type Ca(2+) currents could be recorded in the murine ileum smooth muscle cells, but T-type currents were not affected by the lack of Ca(V)beta(3). Both proteins, Ca(V)beta(2) and Ca(V)beta(3) are localized near the plasma membrane and the localization of Ca(V)beta(2) is not altered in Ca(V)beta(3) deficient cells. Spontaneous contractions and potassium and carbachol induced contractions are not significantly different between ileum longitudinal smooth muscle strips from mice of both genotypes. In summary the data show that in ileum smooth muscle cells, Ca(V)beta(3) has only subtle effects on L-type Ca(2+) currents, appears not to be required for spontaneous and potassium induced contraction but might have a function beyond being a Ca(2+) channel subunit.
authors.affiliation: Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Universität des Saarlandes, D-66421 Homburg, Germany. brigitte.held@uks.eu
authors.forename: Brigitte
authors.initials: B
authors.lastname: Held
authors.forename: Volodymyr
authors.initials: V
authors.lastname: Tsvilovskyy
authors.forename: Marcel
authors.initials: M
authors.lastname: Meissner
authors.forename: Lars
authors.initials: L
authors.lastname: Kaestner
authors.forename: Andreas
authors.initials: A
authors.lastname: Ludwig
authors.forename: Sven
authors.initials: S
authors.lastname: Mossmang
authors.forename: Peter
authors.initials: P
authors.lastname: Lipp
authors.forename: Marc
authors.initials: M
authors.lastname: Freichel
authors.forename: Veit
authors.initials: V
authors.lastname: Flockerzi
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000032:analysis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004553:Electric Conductivity; D007082:Ileum / Q000502:physiology*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques
chemical_list: C491528:Cacnb2 protein, mouse; C510225:Cacnb3 protein, mouse; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D053496:Inositol 1,4,5-Trisphosphate Receptors