CONTRIBUTION OF SURFACE EPITHELIAL-CELLS TO TOTAL CONDUCTANCE OF NECTURUS GASTRIC FUNDUS MUCOSA

Microelectrode techniques were used to quantify the contribution of su rface epithelial cells (SEC) to transepithelial conductance (g(t)) of Necturus gastric fundus mucosa. Transepithelial voltage (V-t) and resi stance (R(t)) as well as the basolateral cell membrane potential (V-b) and voltage divider ratio of SEC were measured. Freshly mounted prepa rations did not respond to luminal amiloride (10 mu M), but within 2-3 h a significant response developed (Delta V-t = 3.8 +/- 1.2 mV, Delta R(t) = 63 +/- 23 Omega . cm(2), and Delta V-b = -6.9 +/- 1.3 mV), ind icating activation of an apical Na+ conductance in SEC. Using circuit analysis equations, we calculate that SEC contribute 10.4% to g(t) und er control conditions and 13.0% after Na+ conductance activation. Hist amine (0.1 mM), which stimulates the oxyntopeptic cells (OC), increase d V-t and decreased R(t) but did not significantly alter the membrane resistances of SEC. As a result, the contribution of SEC to g(t) fell to 7.4 or 9.3%, respectively. The data confirm that SEC are poorly per meable and that the major conductance path across gastric mucosa leads through OC in the glands. The reason for the protracted in vitro acti vation of the apical Na+ conductance in SEC is not known.