Control of ion transport in the thyroid: prostaglandin E2 activates cation transport on the basal membrane of cultured porcine thyroid cell monolayers.

Confluent monolayers of cultured porcine thyroid cells transport fluid from the apical to the basal surface, forming circumscribed zones of detachment (domes) from the culture dish substrate. Stimulation of fluid transport by prostaglandin E2 (PGE2; 1 mumol/l) was associated with an increase in transepithelial potential (TEP). Intracellular potentials (equal to the potential difference across the apical membrane of the cell, Eapical) and the TEP were measured in individual domes so that the potential difference across the basal membrane of the cell (Ebasal) could be calculated from the relationship TEP = Eapical-Ebasal. The PGE2-induced increase in TEP was associated with hyperpolarization of the basal membrane, accompanied by a slight depolarization of the apical membrane. Lines of best fit by least-squares regression showed Eapical = -20.3 mV +0.219 TEP (correlation coefficient r = 0.627; P less than 0.001) and Ebasal = -20.3 mV -0.781 TEP (r = 0.944; P less than 0.001). Phenamil (1 mumol/l), a Na+ channel selective amiloride analogue, reduced the TEP from 13.25 +/- 0.58 (S.E.M.; n = 56) to 2.39 +/- 0.16 mV (n = 51; P less than 0.001) and hyperpolarized the apical membrane potential from -20.7 +/- 0.68 (n = 60) to -32.2 +/- 0.83 mV (n = 105; P less than 0.001). The response of the TEP to phenamil was immediate, and was promptly reversed on washing; in contrast, addition of 5-(N-ethyl-N-isopropyl)amiloride (20 mumol/l; selective for Na+/H+ antiporters) resulted in a slow depolarization over 30 min with a slow recovery after washout.(ABSTRACT TRUNCATED AT 250 WORDS)