Fig. 2. (A) Schematic drawing of the structure of the amphibian gastric mucosa and of the technique employed to record [Ca2+] changes in the gastric gland lumen (a) or in the interstitial space at the basolateral side of the epithelium (b). (B) [Ca2+] changes recorded in the interstitial space underlying the basolateral membrane of oxyntopeptic cells in response to two sequential stimulations with carbachol (100 µM). Upper traces: transepithelial potential (Vt) in mV, mucosal surface negative; lower traces: local [Ca2+] measured in the basolateral space of the gland cells ([Ca2+]bl). (C) Recordings with double-barreled microelectrode in the gland lumen. Upper trace: transepithelial potential (Vt) in mV. Middle trace: gland lumen potential (Vgl) in mV. Bottom trace: [Ca2+] changes in the gland lumen ([Ca2+]gl) in response to carbachol. (D) Effect of hyperpolarization of the epithelium, induced by a current pulse to mimic the transepithelial response to carbachol, on gland lumen [Ca2+]; control response to carbachol is shown for comparison.