title: Characterisation of the ionic currents in freshly isolated rat ureter smooth muscle cells: evidence for species-dependent currents.
abstract: To better understand excitability, and hence contraction, the ionic currents underlying the action potential were identified and characterised in enzymatically isolated smooth muscle cells of the rat ureter. Using the whole-cell patch-clamp, under voltage-clamp conditions with K(+) in the pipette, three types of responses occurred to depolarisation: (1) sustained outward current and spontaneous transient outward currents (STOCs); (2) inward current; and (3) fast outward current. Investigation using different voltage protocols and pharmacological blockers and agonists revealed the presence of three outward and two inward currents. The outward currents were: (1) a sustained BK current, sensitive to low concentrations of tetraethylammonium (TEA) and featuring bursts of STOCs superimposed on it; (2) a fast, transient, A-type K current sensitive to 4-aminopyridine; and (3) a TEA and Ca(2+)-insensitive, late K(+) rectifier current. The inward currents were: (1) a fast L-type Ca(2+) channel current sensitive to nifedipine, Cd(2+) and potentiated by Ba(2+); and (2) a Ca(2+)-sensitive Cl(-) channel, which was inhibited by niflumic acid and Ba(2+), and produced a large tail current upon repolarisation at the end of the voltage step. The I- V relationships and peak amplitudes of all the currents are described. The finding of a K(+) rectifier and Ca(2+)-activated Cl(-) channel distinguish the rat ureteric cells from those of the guinea-pig. Thus, as well as the previously established difference in sarcoplasmic reticulum Ca(2+)-release mechanisms, there is also a species difference in ion channel expression in this tissue. We relate these currents to their possible contribution to the characteristically extremely long lasting action potential in the rat ureter.
authors.affiliation: The Physiological laboratory, University of Liverpool, Crown Street, Liverpool L69 3BX, UK.
authors.forename: R D
authors.initials: RD
authors.lastname: Smith
authors.forename: L
authors.initials: L
authors.lastname: Borisova
authors.forename: Susan
authors.initials: S
authors.lastname: Wray
authors.forename: T
authors.initials: T
authors.lastname: Burdyga
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D004553:Electric Conductivity; D005260:Female; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D013045:Species Specificity; D019789:Tetraethylammonium / Q000494:pharmacology; D014513:Ureter / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
chemical_list: D007473:Ion Channels; D026902:Potassium Channel Blockers; D002104:Cadmium; D001464:Barium; D019789:Tetraethylammonium; D015761:4-Aminopyridine