Nonselective cation channel as a Ca2+ influx pathway in pepsinogen-secreting cells of bullfrog esophagus

Abstract

In pepsinogen-secreting cells of bullfrog ( Rana catesbeiana), recent evidence suggests that Ca2+ release from internal stores followed by Ca2+ influx across the plasma membrane elicits pepsinogen secretion. Such a Ca2+ influx could be carried by a background current, potentiated by bombesin, that was found in these cells using the whole cell patch-clamp technique. The permeability ratio of Cs+-Rb+-K+-Na+-Li+- N-methyl-d-glucamine+-Ca2+was 1.01:1:1:0.86:0.72:0.54:0.34. The current was almost totally blocked by the nonselective cation channel blockers La3+(0.1 mM) and Gd3+ (0.1 mM) and was activated by intracellular Ca2+. These properties demonstrated that the current, which was activated by bombesin, was a nonselective cation current. At the same time, Gd3+ suppressed pepsinogen secretion by 29 ± 5.6% in isolated pepsinogen-secreting glands. These results are in accord with the idea that a nonselective cation channel in pepsinogen-secreting cells plays a role as a Ca2+ influx pathway leading to secretion of pepsinogen in bullfrog esophageal mucosa.