Ion transport in rat antral mucosa in vitro: general characteristics

Although numerous studies have shown the existence of various types of ion conductance in antral part of gastric fundus mucosa epithelia of amphibian, practically no data are available on ion conductance in higher animal species. Present experiments were undertaken to check the possible existence of ion conductance in rat gastric antral mucosa and to investigate its general electrophysiological characteristics. Antral epithelia were isolated from adult Sprague Dawley rats. The tissues were mounted to a modified Ussing-type chamber and continually perfused with identical Krebs-Henseleit bicarbonate buffer on both sides. Antrum generated a transepithelial electrical potential difference (Vt = -10 +/- 2.6 mV) and short-circuit current (Isc = 76 +/- 15 microA.cm-2) with a transepithelial electrical resistance (Rt = 135 +/- 16.8 Ohm.cm2). Ion replacement experiments showed that it is mainly Na+ transport that contributes to Vt and Isc as evidenced by a) Na+ and/or Cl- removal, b) the effects of amiloride a sodium channel blocker, on the apical (secretory) surface, c) the effects of the Na(+)-K(+)-ATPase inhibitor ouabain on the basolateral (nutrient) side of the epithelium. Microelectrode experiments confirmed the existence of Na+ and/or Cl- conductance of the apical cell membrane. Antral mucosa also showed a gradual and time-dependent increase in sensitivity to amiloride (10(-5) mol/l). Maximum inhibition of Vt and Isc by amiloride in dose-dependent manner was detected after 1-2 h. This amiloride-sensitive sodium transport (maximal level 31.5 +/- 5.9 microA.cm-2) represented approximately 50% of the whole transepithelial ion conductance. Results of experiments with ouabain (10(-4 mol/l) suggest the presence of functional Na(+)-K(+)-ATPase and/or Na(+)-ATPase in the basolateral cell membranes. Which signals trigger this epithelial ion transport, which hormones are responsible for its regulation and what is the physiological significance of this ion conductance remains to be elucidated.