Expression of low voltage-activated calcium channels inXenopus oocytes |
| |
Authors: | I. A. Dzhura V. G. Naidenov O. P. Lyubanova P. G. Kostyuk Ya. M. Shuba |
| |
Affiliation: | (1) Bogomolets Institute of Physiology, National Academy of Sciences of Ukraine, Kiev, Ukraine |
| |
Abstract: | Calcium channels were expressed inXenopus oocytes by means of messenger RNA extracted from the rat thalamo-hypothalamic complex, mRNA(h). Inward barium currents,IBa, were recorded in Cl–-free extracellular solution with 40 mM Ba2+ as a charge carrier, using two-microelectrode technique. Depolarizations from a very negative holding potential (Vh=–120 mV) began to activateIBa at about –80 mV; this current peaked at –30 to –20 mV and reversed at +50 mV, indicating that IBa may be transferred through the low voltage-activated (LVA) calcium channels. The time-dependent inactivation of the current during a prolonged depolarization to –20 mV was quite slow, followed a single exponential decay with a time constant of 1550 msec, and contained a residual component constituting 30% of the maximum amplitude. The current could not be completely inactivated at any holding potential. As expected for LVA current, a steady-state inactivation curve was shifted towards negative potentials. It could be described by the Boltzmann's equation with the half-inactivation potential of –78 mV, slope factor of 15 mV, and residual level of 0.3. ExpressedIBa could be blocked by flunarizine (Kd=0.42 µM), nifedipine (Kd=10 µM), and amiloride at a 500 µM concentration. Among the inorganic Ca2+ channel blockers, the most potent was La3+ (Kd=0.48 µM), while Cd2+ and Ni2+ were not very selective and almost thousand-fold less effective (Kd=0.52 mM andKd=0.62 mM, respectively) than La3+. Our data show that mRNA(h) induces expression in the oocytes of almost exclusively LVA Ca2+ channels with voltage-dependent and pharmacological properties very similar to those observed for T-type Ca2+ current in native hypothalamic neurons, though kinetic properties of the expressed and natural currents are somewhat different.Neirofiziologiya/Neurophysiology, Vol. 27, No. 3, pp. 183–189, May–June, 1995. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|