title: Crosstalk between voltage-independent Ca2+ channels and L-type Ca2+ channels in A7r5 vascular smooth muscle cells at elevated intracellular pH: evidence for functional coupling between L-type Ca2+ channels and a 2-APB-sensitive cation channel.
abstract: This study was designed to investigate the role of voltage-independent and voltage-dependent Ca2+ channels in the Ca2+ signaling associated with intracellular alkalinization in A7r5 vascular smooth muscle cells. Extracellular administration of ammonium chloride (20 mmol/L) resulted in elevation of intracellular pH and activation of a sustained Ca2+ entry that was inhibited by 2-amino-ethoxydiphenyl borate (2-APB, 200 micromol/L) but not by verapamil (10 micro;mol/L). Alkalosis-induced Ca2+ entry was mediated by a voltage-independent cation conductance that allowed permeation of Ca2+ (PCa/PNa approximately 6), and was associated with inhibition of L-type Ca2+ currents. Alkalosis-induced inhibition of L-type Ca2+ currents was dependent on the presence of extracellular Ca2+ and was prevented by expression of a dominant-negative mutant of calmodulin. In the absence of extracellular Ca2+, with Ba2+ or Na+ as charge carrier, intracellular alkalosis failed to inhibit but potentiated L-type Ca2+ channel currents. Inhibition of Ca2+ currents through voltage-independent cation channels by 2-APB prevented alkalosis-induced inhibition of L-type Ca2+ currents. Similarly, 2-APB prevented vasopressin-induced activation of nonselective cation channels and inhibition of L-type Ca2+ currents. We suggest the existence of a pH-controlled Ca2+ entry pathway that governs the activity of smooth muscle L-type Ca2+ channels due to control of Ca2+/calmodulin-dependent negative feedback regulation. This Ca2+ entry pathway exhibits striking similarity with the pathway activated by stimulation of phospholipase-C-coupled receptors, and may involve a similar type of cation channel. We demonstrate for the first time the tight functional coupling between these voltage-independent Ca2+ channels and classical voltage-gated L-type Ca2+ channels.
authors.affiliation: Department of Pharmacology and Toxicology, School of Medicine, Yamagata University, Yamagata, Japan.
authors.forename: Michael
authors.initials: M
authors.lastname: Poteser
authors.forename: Ichiro
authors.initials: I
authors.lastname: Wakabayashi
authors.forename: Christian
authors.initials: C
authors.lastname: Rosker
authors.forename: Margot
authors.initials: M
authors.lastname: Teubl
authors.forename: Rainer
authors.initials: R
authors.lastname: Schindl
authors.forename: Nikolai M
authors.initials: NM
authors.lastname: Soldatov
authors.forename: Christoph
authors.initials: C
authors.lastname: Romanin
authors.forename: Klaus
authors.initials: K
authors.lastname: Groschner
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
chemical_list: D001896:Boron Compounds; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002147:Calmodulin; D000643:Ammonium Chloride; D001127:Arginine Vasopressin; D001464:Barium; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium