Ca2+ currents in human colonic smooth muscle cells.
Voltage-gated Ca2+ currents were investigated in single smooth muscle cells freshly isolated from the circular layer of the human colon (ascending and descending portions) using the whole cell voltage-clamp technique. Tissue samples were obtained at the time of therapeutic surgery. In physiological salt solution (containing 2 mM Ca2+), an inward current was observed when the cell membrane was depolarized in the presence of tetrodotoxin. This current disappeared when Ca2+ was removed from the bath solution and was inhibited when Ca2+ channel blockers were applied, indicating that the inward current was a Ca2+ current (ICa). Changing the holding potential (HP) from -100 mV to more positive potentials (e.g., -60 and -40 mV) markedly decreased the amplitude of ICa. The voltage dependence of steady-state activation and inactivation was represented by Boltzmann distributions; there was a substantial amount of overlap (window current) between -60 and -10 mV. A fast-inactivating ICa component followed by a slow-inactivating ICa component was observed in some cells from both ascending and descending colons. The fast ICa component was observed only when cells were held at -80 or -100 mV, and had a more negative threshold potential (-70 to -60 mV). This component was sensitive to low concentrations of Ni2+ (30 microM) but was resistant to nifedipine (10-20 microM). In contrast, the slow (sustained) ICa component was observed at all HPs (-40 to -100 mV) and had a more positive threshold potential (about -40 mV). This component was insensitive to low concentration of Ni2+ but was sensitive to nifedipine and BAY K 8644.(ABSTRACT TRUNCATED AT 250 WORDS)
Xiong
Z
Z
Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Ohio 45267, USA.
Sperelakis
N
N
Noffsinger
A
A
Fenoglio-Preiser
C
C
D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D003106:Colon / Q000166:cytology / Q000502:physiology*; D004594:Electrophysiology; D006706:Homeostasis; D006801:Humans; D008875:Middle Aged; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology*; D013997:Time Factors
D002118:Calcium