title: T- and L-type Ca2+ currents in freshly dispersed smooth muscle cells from the human proximal urethra.
abstract: The purpose of the present study was to characterise Ca2+ currents in smooth muscle cells isolated from biopsy samples taken from the proximal urethra of patients undergoing surgery for bladder or prostate cancer. Cells were studied at 37 degrees C using the amphotericin B perforated-patch configuration of the patch-clamp technique. Currents were recorded using Cs+-rich pipette solutions to block K+ currents. Two components of current, with electrophysiological and pharmacological properties typical of T- and L-type Ca2+ currents, were present in these cells. When steady-state inactivation curves for the L current were fitted with a Boltzmann equation, this yielded a V1/2 of -45+/-5 mV. In contrast, the T current inactivated with a V1/2 of -80+/-3 mV. The L currents were reduced in a concentration-dependent manner by nifedipine (ED50=159+/-54 nM) and Ni2+ (ED50=65+/-16 microM) but were enhanced when external Ca2+ was substituted with Ba2+. The T current was little affected by TTX, reduction in external Na+, application of nifedipine at concentrations below 300 nM or substitution of external Ca2+ with Ba2+, but was reduced by Ni2+ with an ED50 of 6+/-1 microM. When cells were stepped from -100 to -30 mV in Ca2+-free conditions, small inward currents could be detected. These were enhanced 40-fold in divalent-cation-free solution and blocked in a concentration-dependent manner by Mg2+ with an ED50 of 32+/-16 microM. These data support the idea that human urethral myocytes possess currents with electrophysiological and pharmacological properties typical of T- and L-type Ca2+ currents.
authors.affiliation: Smooth Muscle Group, Department of Physiology, The Queen's University of Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK. m.hollywood@qub.ac.uk
authors.forename: M A
authors.initials: MA
authors.lastname: Hollywood
authors.forename: Siobhan
authors.initials: S
authors.lastname: Woolsey
authors.forename: I K
authors.initials: IK
authors.lastname: Walsh
authors.forename: P F
authors.initials: PF
authors.lastname: Keane
authors.forename: N G
authors.initials: NG
authors.lastname: McHale
authors.forename: K D
authors.initials: KD
authors.lastname: Thornbury
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D020747:Calcium Channels, T-Type / Q000502:physiology*; D004594:Electrophysiology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D032342:Muscle Cells / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D012996:Solutions; D014521:Urethra / Q000166:cytology* / Q000502:physiology*
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D012996:Solutions; D001464:Barium; D009532:Nickel; D009543:Nifedipine; D002118:Calcium