Properties of inward calcium current in guinea pig ureteral myocytes.
Ureteral myocytes of guinea pigs have L-type Ca2+ channels (I(Ca)). In 3 mM Ca2+, maximum I(Ca) was 3.38 microA/cm2. Voltage at which conductance is 50% of maximum (V0.5) of I(Ca) was -1.0 mV in 3 mM Ca2+ and +22 mV in 30 mM Ca2+, with slope factors of 8 mV. V0.5 of steady-state inactivation of I(Ca) was -16.2 and +1.1 mV in 3 and 30 mM Ca2+, respectively, with similar slope factors of about -6 mV. A window current reaching 20-25% of the maximum I(Ca) was active between -20 and 0 mV. I(Ca) inactivated very slowly, with time constants of 217.6 and 2,455.9 ms with no voltage dependency. When Ba2+ was used as the charge carrier, the amplitude and inactivation kinetics of the Ba2+ current were similar to those for I(Ca). These results indicate that the ureteral myocyte has little Ca2+-mediated Ca2+ channel inactivation, a feature significantly associated with the slow I(Ca) inactivation. The slow inactivation and the window current are essential for the sustained membrane depolarization during the plateau of ureteral action potentials.
Sui
J L
JL
Department of Pharmacology, State University of New York Health Science Center at Brooklyn, 11203, USA.
Kao
C Y
CY
D000818:Animals; D002118:Calcium / Q000502:physiology*; D004553:Electric Conductivity; D006168:Guinea Pigs; D006706:Homeostasis; D007700:Kinetics; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D014513:Ureter / Q000166:cytology / Q000502:physiology*
D002118:Calcium