Intracellular and luminal ion concentrations in sea turtle salt glands determined by x-ray microanalysis

Summary

The lachrymal salt glands of hatchlings of the green sea turtle (Chelonia mydas) secrete a hyperosmotic (up to 2000 mosmol·kg⁻¹) NaCl solution. X-ray microanalysis of frozen-hydrated glands showed that during secretion intracellular Na⁺ concentration in the principal cells increased from 13 to 34 mmol·l⁻¹ of cell water, whilst Cl⁻ and K⁺ concentrations remained unchanged at 81 mmol·l⁻¹ and 160–174 mmol·l⁻¹, respectively. The high Cl⁻ concentration and the change in Na⁺ concentration are consistent with the prevailing paradigm for secretion by the structurally and functionally similar elasmobranch rectal gland. Concentrations of Na⁺, Cl⁻ and K⁺ in the lumina of secretory tubules of secreting (Na⁺ 122, Cl⁻ 167, K⁺ 38 mmol·l⁻¹) and non-secreting (Na⁺ 114, Cl⁻¹ 174, K⁺ 44 mmol·l⁻¹) glands were similar and the fluid was calculated to be approximately isosmotic with blood. In the central canals Na⁺ and Cl⁻ concentrations were similar but K⁺ concentration was lower (11–15 mmol·l⁻¹). It is concluded that either a high transepithelial NaCl gradient in secretory tubules and central canals is very rapidly dissipated during the short time between gland excision and freezing, or that ductal modification of an initial isosmotic secretion occurs.