T- and L-type Ca 2+ currents in freshly dispersed smooth muscle cells from the human proximal urethra

Hollywood, Mark A. and Woolsey, Siobhan M. and Walsh, I.K. and Keane, P.F. and McHale, Noel G. and Thornbury, Keith D. (2003) T- and L-type Ca 2+ currents in freshly dispersed smooth muscle cells from the human proximal urethra. J Physiol, 550 (3). pp. 753-764.

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Abstract

The purpose of the present study was to characterise Ca 2+ currents in smooth muscle cells solated from biopsy samples taken from the proximal urethra of patients undergoing surgery for bladder or prostate cancer. Cells were studied at 37°C using the amphotericin B perforated-patch onfiguration 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 Ca 2+ currents, were present in these cells. When steady-state inactivation curves for the L current were fitted with a Boltzmann equation, this yielded a VÎ of _45 ± 5 mV. In contrast, the T current inactivated with a VÎ of _80 ± 3 mV. The L currents were reduced in a concentration-dependent manner by nifedipine (ED50 = 159 ± 54 nM) and Ni 2+ (ED50 = 65 ± 16 mM) but were enhanced when external Ca 2+ was substituted with Ba 2+ . The T current was little affected by TTX, reduction in external Na + , application of nifedipine at concentrations below 300 nM or substitution of external Ca 2+ with Ba 2+ , but was reduced by Ni 2+ with an ED50 of 6 ± 1 mM. When cells were stepped from _100 to _30 mV in Ca 2+ -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 Mg 2+ with an ED50 of 32 ± 16 mM. These data support the idea that human urethral myocytes possess currents with electrophysiological and pharmacological properties typical of T- and L-type Ca 2+ currents.

Item Type:	Article
Uncontrolled Keywords:	Adult; Aged; Algorithms; Barium/pharmacology; Calcium/pharmacology; Calcium Channel Blockers/pharmacology; Calcium Channels, L-Type/physiology; Calcium Channels, T-Type/physiology; Electrophysiology; Female; Humans; Male Middle Aged; Muscle Cells/physiology; Muscle, Smooth/cytology; Muscle, Smooth/physiology; Nickel/pharmacology; Nifedipine/pharmacology; Patch-Clamp Techniques Solutions; Urethra/cytology; Urethra/physiology
Subjects:	Science
Research Centres:	Smooth Muscle Research Centre
Depositing User:	Concepta Woods
Date Deposited:	08 Mar 2012 10:17
Last Modified:	11 Nov 2014 16:10
URI:	https://eprints.dkit.ie/id/eprint/197

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