Effects of removal of calcium from bathing media on frog stomach

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Abstract
Removal of Ca++ from the solutions bathing the frog gastric mucosa results in an initial increase in resistance (first phase) and a subsequent marked decrease in resistance (second phase). During the first phase the H+ secretory rate is decreased by 39% and the potential difference (PD) by 10%. During the second phase the measured H+ rate decreased to zero and the PD to near zero. Anoxia or DNP, which ordinarily produce a marked increase in resistance, failed to do so in the absence of Ca++. Comparable effects of Ca++ removal are found with Cl–-free bathing solutions. Replacement of Ca++ to the secretory solution on the nutrient side reversed these effects. Addition of Ca++ to the secretory solution readily reversed the second phase but only partly reversed the first phase. The inability of Ca++ on the secretory side in contrast to Ca++ on the nutrient side to reverse completely the first phase indicates that the secretory membrane may be much less permeable to Ca++ than the nutrient membrane.

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