title: Modulation of the hyperpolarization-activated current (I(f)) by calcium and calmodulin in the guinea-pig sino-atrial node.
abstract: The aim of this study was to investigate possible regulation of the hyperpolarization-activated current (I(f)) by cytosolic calcium in guinea-pig sino-atrial (SA) node cells. Isolated SA node cells were superfused with physiological saline solution (36 degrees C) and the perforated patch voltage-clamp technique used to record I(f) activated by hyperpolarizing voltage steps. A 10-min loading of SA node cells with the calcium chelator BAPTA (using 10 microM BAPTA-AM) significantly reduced the amplitude of I(f) at all potentials studied (69+/-8% at -80 mV, n=6). BAPTA loading also shifted the voltage of half-activation (V(h)) of the conductance from -83+/-2 mV in control to -93+/-2 mV in BAPTA (n=6) without significantly altering the slope of activation. The calmodulin antagonists W-7 (10 microM), calmidazolium (25 microM) and ophiobolin A (20 microM) caused similar reductions in I(f) amplitude (73+/-4, 86+/-9 and 59+/-6% at -80 mV, n=6, 5 and 4, respectively) and shifts in V(h) (11+/-3, 14+/-3 and 8+/-2 mV). In cells pre-treated with W-7, exposure to BAPTA caused no further reduction in current amplitude (n=6). I(f) current amplitude was unaffected by the calmodulin dependent kinase (CaMKII) inhibitor KN-93 (1 microM) although this CaMKII inhibition did reduce L-type calcium by 48+/-19% at 0 mV (n=3). These results are consistent with a role for calcium and calmodulin in the regulation of I(f), via a mechanism that is independent of CaMKII. Alterations in intracellular calcium during the cardiac cycle may be involved in fine tuning the voltage-dependent properties of I(f) and may thus determine its relative contribution to pacemaking in the SA node.
authors.affiliation: Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK.
authors.forename: Lauren
authors.initials: L
authors.lastname: Rigg
authors.forename: Paul A D
authors.initials: PA
authors.lastname: Mattick
authors.forename: Bronagh M
authors.initials: BM
authors.lastname: Heath
authors.forename: Derek A
authors.initials: DA
authors.lastname: Terrar
mesh_terms: D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000502:physiology*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels; D047428:Protein Kinase Inhibitors; D012849:Sinoatrial Node / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology; D000096926:Benzenesulfonamides
chemical_list: D001596:Benzylamines; D002118:Calcium; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin; D002614:Chelating Agents; D054815:Cyclic Nucleotide-Gated Cation Channels; D004533:Egtazic Acid; D004791:Enzyme Inhibitors; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D015221:Potassium Channels; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; C072105:KN 93; D000096926:Benzenesulfonamides; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; C017967:W 7