Membrane currents in a calcitonin-secreting human C cell line.
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.
Biagi
B A
BA
Department of Physiology, Ohio State University, Columbus 43210-1239.
Mlinar
B
B
Enyeart
J J
JJ
D002116:Calcitonin / Q000378:metabolism*; D002277:Carcinoma / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D004594:Electrophysiology; D006801:Humans; D007700:Kinetics; D011188:Potassium / Q000502:physiology; D012964:Sodium / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D013964:Thyroid Neoplasms / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D014407:Tumor Cells, Cultured
D013779:Tetrodotoxin; D002116:Calcitonin; D012964:Sodium; D011188:Potassium