Sodium channel heterogeneity in the apical membrane of porcine thyroid epithelial cells.
Porcine thyroid epithelial cells cultured as a monolayer with their apical membranes facing the medium are known to absorb Na+ and secrete Cl-. Two types of Na+ channels were found in cell-attached patches of apical membrane. A low conductance Na+ channel (conductance g = 4 picosiemens (pS)) remained open for seconds and showed a high selectivity for Na+ compared with K+. In contrast, a high conductance Na+ channel (g = 10 pS) flickered rapidly and had reduced selectivity. Both types of Na+ channel became more prevalent when the cells were exposed to Na(+)-free medium, though only the high conductance channel increased in prevalence on addition of prostaglandin E2, a stimulator of adenylate cyclase which increases Na+ absorption in this cultured epithelium. Two minority types of channel were also found: a non-selective small conductance cation channel which had been reported previously, and an intermediate conductance channel found only in Na(+)-free medium. It was concluded that passage of Na+ across the apical membrane of thyroid cells is mediated by typical epithelial Na+ channels, but that the two types of channel are differentially regulated.
Bourke
J R
JR
Department of Physiology and Pharmacology, University of Queensland, Australia.
Abel
K C
KC
Huxham
G J
GJ
Sand
O
O
Manley
S W
SW
D000818:Animals; D002478:Cells, Cultured; D015232:Dinoprostone / Q000494:pharmacology; D004848:Epithelium / Q000378:metabolism; D017136:Ion Transport; D015222:Sodium Channels / Q000378:metabolism*; D013552:Swine; D013961:Thyroid Gland / Q000378:metabolism*
D015222:Sodium Channels; D015232:Dinoprostone