title: 4-aminopyridine affects rat arterial smooth muscle BK(Ca) currents by changing intracellular pH.
abstract: The hypothesis whether or not 4-AP can affect vascular smooth muscle BK(Ca) currents was tested using the patch-clamp technique, pH- and calcium-fluorimetry, and freshly isolated rat arterial smooth muscle cells. Application of 4-AP reversibly inhibited BK(Ca) currents at an intracellular calcium ([Ca](i)) of 250 nM with a half-block of 2. 5 mM at +50 mV. The presence of 2 microM thapsigargin, 10 microM heparin, and 10 microM ryanodine did not alter the effect of 4-AP on BK(Ca) currents at [Ca](i) 250 nM. At [Ca](i)<100 nM 4-AP did not inhibit BK(Ca) currents. Application of 4-AP to the intracellular or extracellular side of excised BK(Ca) channels did not alter channel activity or channel amplitude. Replacement of the pH-sensitive calcium buffer EGTA by the pH-insensitive calcium buffer BAPTA in the intracellular solution turned the 4-AP-induced inhibition of BK(Ca) currents into a stimulation at [Ca](i) 250 nM. Application of 4-AP to single cells increased intracellular pH, which was accompanied by a reduction of [Ca](i) in EGTA-loaded cells and a stable [Ca](i) in BAPTA-loaded cells. Thus, these results suggest that in isolated vascular smooth muscle cells at [Ca](i)>100 nM 4-AP affects BK(Ca) currents via an alteration of intracellular pH.
authors.affiliation: Institute of Biophysics, Bulgarian Academy of Sciences, Acad. Bonchev Str., Bl. 21, 1113 Sofia, Bulgaria.
authors.forename: P
authors.initials: P
authors.lastname: Petkova-Kirova
authors.forename: H
authors.initials: H
authors.lastname: Gagov
authors.forename: U
authors.initials: U
authors.lastname: Krien
authors.forename: D
authors.initials: D
authors.lastname: Duridanova
authors.forename: T
authors.initials: T
authors.lastname: Noack
authors.forename: R
authors.initials: R
authors.lastname: Schubert
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000166:cytology; D002118:Calcium / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D006863:Hydrogen-Ion Concentration; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated; D051381:Rats; D011921:Rats, Inbred WKY; D051640:Small-Conductance Calcium-Activated Potassium Channels
chemical_list: D002614:Chelating Agents; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D051640:Small-Conductance Calcium-Activated Potassium Channels; D004533:Egtazic Acid; D015761:4-Aminopyridine; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium