Hyperpolarization of thyroid cells in vitro by thyrotropin and cyclic AMP.
With the use of microelectrodes, membrane potential (MP) was measured in mouse thyroid glands in vitro. A basal resting MP of about -39 mV was confirmed. The initial effect of feeding a low-iodine diet (6-12 days) was hyperpolarization, up to -47 m V; chronic low-iodine diet led to depolarization. Low concentrations of thyrotropin (less than 3 mU/ml superfusate) caused hyperpolarization and high ones (greater than 10 mU/ml) led to depolarization. Cyclic AMP (10(-3) M), dibutyryl cyclic AMP (1.2 X 10(-4) M or 1.2 X 10(-3) M) and theophylline (10(-2) or 10(-3) M) caused similar hyperpolarization: D- and DL-propranolol (5 X 10(-5) -5 X 10(-4) M) produced depolarization and inhibited hyperpolarization by thyrotropin. Conclusions are that hyperpolarization is a consequence of short-term increased secretion of thyrotropin in vivo or of low (near physiological) concentrations in vitro; these effects are probably mediated by cyclic AMP. The relationship to and mechanism of depolarization resulting from chronic enhanced endogenous secretion or high in vitro concentrations of thyrotropin are unknown.
D000818:Animals; D000242:Cyclic AMP / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008564:Membrane Potentials / Q000187:drug effects*; D051379:Mice; D008839:Microelectrodes; D011433:Propranolol / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology; D013961:Thyroid Gland / Q000187:drug effects / Q000502:physiology*; D013972:Thyrotropin / Q000494:pharmacology*
D013972:Thyrotropin; D011433:Propranolol; D013806:Theophylline; D000242:Cyclic AMP