Continuous monitoring of potassium efflux from rat parotid gland fragments by potassium selective electrodes

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Abstract
The concentration of potassium ions in a superfusate of rat parotid gland fragment was continuously monitored by potassium selective electrodes to assess the rate of potassium secretion by the gland. The potassium concentration determined from the electrode readings agreed well with values obtained by atomic absorption (r = 0.99). The detection limit for changes in potassium concentration was approximated to 50 μ K+. When medium was recirculated over the gland fragments it was possible to detect even small changes in the rate of potassium efflux. Thus, increases in potassium secretion following administration of substance P (SP) down to 0.1 nM and carbacholine 10 nM was registered. When the buffer medium was passed only once over the gland fragments it was possible to reproducibly study the time course of potassium secretion. However, with this system higher doses of secretagogues were required for detection of potassium efflux, since the potassium secernated was diluted by the perifused buffer. Following SP (0.01 or 0.1 μ) or carbacholine (1 or 10 μ) a peak of potassium secretion was registered during the first 8–10 min, which was followed by a steady low rate. The metabolic state of the gland fragments, as determined by the ratio of adenine nucleotides, was similar to that foundin vivoeven after an experiment of several hours' duration. However, the viable part of the glandular tissue, calculated as the content of adenine nucleotides per mg protein, was decreased to approximately 30% compared to the intact glandin situ.The present results indicate that the potassium efflux from parotid gland fragments may be continuously monitored by means of potassium electrodes placed in contact with buffer that is superfused over the glandular tissue.