Effects of various secretagogues upon42K and22Na uptake duringin vitrohormone release from the rat adenohypophysis

Autor: John V. Milligan, Jacob Kraicer
Rok vydání: 1973
Předmět:
Zdroj: The Journal of Physiology. 232:221-237
ISSN: 0022-3751
Popis: 1. The in vitro uptake of (22)Na and (42)K was measured simultaneously in rat adenohypophyses during hormone release produced by several secretagogues and during inhibition of hormone release in Ca-free media.2. Intracellular adenohypophysial [Na(+)] and [K(+)] changed only slightly when the uptake changed. This would indicate that relative permeability changes were the primary effect of the treatments.3. The uptake of (42)K was increased by elevated external [K(+)], but was unaffected by the presence or absence of Ca(2+). Acid extracts of hypothalamus-stalk-median eminence or cerebellum also increased the (42)K uptake.4. The uptake of (22)Na or (24)Na was decreased by elevated [K(+)]. Uptake was increased in Ca-free Krebs-Ringer bicarbonate; but was unaltered when [K(+)] was concurrently increased.5. Neither purified growth hormone releasing hormone, synthetic lysine-vasopressin, dibutyryl cyclic AMP nor theophylline had an effect on the uptake of either K(+) or Na(+).6. The rapid uptake of (22)Na and its smaller volume of distribution compared to absolute measurements of intracellular [Na(+)] suggest that the plasma membrane of adenohypophysial cells is relatively impermeable to Na(+).7. We conclude that changes in the uptake of Na(+) and K(+) associated with hormone release are incidental to the release process.8. Hormone release produced by elevated external [K(+)] is most likely due to a non-specific increase in permeability of the cell membranes, facilitating Ca(2+) entry into the cytoplasm.9. The results suggest that the low resting transmembrane potentials of adenohypophysial cells may be due to their conjoint relatively high permeability to both K(+) and Ca(2+), rather than K(+) and Na(+).
Databáze: OpenAIRE
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