AJP - Cell Physiology, Vol 263, Issue 5 C986-C994, Copyright © 1992 by American Physiological Society
Membrane currents in a calcitonin-secreting human C cell line
B. A. Biagi, B. Mlinar and J. J. Enyeart
Department of Physiology, Ohio State University, Columbus 43210-1239.
The whole cell version of the patch-clamp technique was used to identify
and characterize voltage-gated Ca2+, Na+, and K+ currents in the
calcitonin-secreting human thyroid TT cell line. Ca2+ current consisted of
a single low-voltage-activated rapidly inactivating component. The current
was one-half maximally activated at a potential of -27 mV, while
steady-state voltage-dependent inactivation was one-half complete at -51
mV. The Ca2+ current inactivated with a voltage-dependent time constant
that reached a minimum of 16 ms at potentials positive to -15 mV.
Deactivation kinetics could also be fit with a single voltage-dependent
time constant of approximately 2 ms at -80 mV. Replacing Ca2+ with Ba2+
reduced the maximum current by 18 +/- 5% (n = 6). The dihydropyridine Ca2+
agonist (-)BAY K 8644 did not affect the Ca2+ current, but 50 microM Ni2+
reduced it by 81 +/- 0.8% (n = 5). TT cells also possessed
tetrodotoxin-sensitive voltage-gated Na+ channels and
tetraethylammonium-sensitive delayed rectifier type K+ currents. These
results indicate that TT cells possess membrane currents necessary for the
generation of action potentials. T-type Ca2+ channels are the sole pathway
for voltage-dependent Ca2+ entry into these cells and may couple electrical
activity to calcitonin secretion.
