Properties of inward calcium current in guinea pig ureteral myocytes
Sui, J.L.; Kao, C.Y.
American Journal of Physiology 272(2 Pt 1): C543-C549
1997
ISSN/ISBN: 0002-9513 PMID: 9124297 Document Number: 475039
Ureteral myocytes of guinea pigs have L-type Ca-2+ channels (I-Ca). In 3 mM Ca-2+, maximum I-Ca was 3.38 mu-A/cm-2. Voltage at which conductance is 50% of maximum (V-05) of I-Ca was - 1.0 mV in 3 mM Ca-2+ and +22 mV in 30 mM Ca-2+, with slope factors of 8 mV. V-0.5 of steady-state inactivation of I-Ca was - 16.2 and + 1.1 mV in 3 and 30 mM Ca-2+, respectively, with similar slope factors of about -6 mV. A window current reaching 20-25% of the maximum IC. 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 Ba-2+ was used as the charge carrier, the amplitude and inactivation kinetics of the Ba-2+ current were similar to those for I-Ca. These results indicate that the ureteral myocyte has little Ca-2+-mediated Ca-2+ 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.