title: Surface charge and lanthanum block of calcium current in bullfrog sympathetic neurons.
abstract: The density of surface charge associated with the calcium channel pore was estimated from the effect of extracellular ionic strength on block by La3+. Currents carried by 2 mM Ba2+ were recorded from isolated frog sympathetic neurons by the whole-cell patch-clamp technique. In normal ionic strength (120 mM N-methyl-D-glucamine, NMG), La3+ blocked the current with high affinity (IC50 = 22 nM at 0 mV). La3+ block was relieved by strong depolarization in a time- and voltage-dependent manner. After unblocking, open channels reblocked rapidly at 0 mV, allowing estimation of association and dissociation rates for La3+: k(on) = (7.2 +/- 0.7) x 10(8) M(-1) s(-1), k(off) = 10.0 +/- 0.5 s(-1). To assess surface charge effects, La3+ block was also measured in low ionic strength (12.5 mM NMG) and high ionic strength (250 mM NMG). La3+ block was higher affinity and faster by two- to threefold in 12.5 mM NMG, with little effect of 250 mM NMG. The data could be described by Gouy-Chapman theory with a surface charge density of approximately 1 e-/3000-4000 A2. These results indicate that there is a small but detectable surface charge associated with the pore of voltage-dependent calcium channels.
authors.affiliation: Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: B M
authors.initials: BM
authors.lastname: Block
authors.forename: W C
authors.initials: WC
authors.lastname: Stacey
authors.forename: S W
authors.initials: SW
authors.lastname: Jones
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D007811:Lanthanum / Q000378:metabolism / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011892:Rana catesbeiana; D013564:Sympathetic Nervous System / Q000502:physiology*; D014783:Viscosity
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007811:Lanthanum