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A description of Ca 2+ channels in human detrusor smooth muscle
Author(s) -
Sui G.P.,
Wu C.,
Fry C.H.
Publication year - 2003
Publication title -
bju international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.773
H-Index - 148
eISSN - 1464-410X
pISSN - 1464-4096
DOI - 10.1046/j.1464-410x.2003.04356.x
Subject(s) - nicardipine , verapamil , chemistry , voltage clamp , membrane potential , patch clamp , electrophysiology , oscillation (cell signaling) , biophysics , current clamp , analytical chemistry (journal) , calcium , medicine , biochemistry , biology , chromatography , organic chemistry
OBJECTIVE To characterize the Ca 2+ channels in human detrusor smooth muscle and to investigate their contribution to spontaneous electrical activity. MATERIALS AND METHODS Isolated human detrusor smooth muscle myocytes were used to measure ionic currents under voltage‐clamp or membrane potential under current‐clamp. Membrane potential oscillations were analysed in terms of oscillation frequency and amplitude using fast Fourier transforms. RESULTS Under voltage‐clamp an inward current dependent on extracellular Ca 2+ was recorded using Cs + ‐filled patch electrodes. The current could be separated into two components on the basis of their sensitivity to Ni 2+ , verapamil or nicardipine, and their dependence on holding and clamp potential. A Ni 2+ ‐sensitive component activated over a relatively negative range of potentials (−60 to −20 mV) comprised about a third of the total current and was designated a T‐type Ca 2+ current. A verapamil/nicardipine‐sensitive component, activated at more positive potentials, was designated an l ‐type Ca 2+ current. Using K + ‐based filling solutions spontaneous transient outward currents were recorded that had the characteristics of current flow through BK channels. Membrane potential oscillations, under current‐clamp increased in frequency but not amplitude as the mean membrane potential was made less negative. The voltage‐dependence of oscillation frequency was similar to that of the l ‐type, but not T‐type, Ca 2+ current activation curve. Furthermore oscillation frequency was slowed by verapamil but not Ni 2+ . CONCLUSION The study showed, for the first time, the presence of both T‐ and L‐type Ca 2+ channels in human detrusor smooth muscle; we propose a role for these channels in spontaneous activity. The results suggest that the L ‐type Ca 2+ current can control membrane potential oscillation frequency. The significance of this finding for spontaneous contractions is discussed.