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Dietary Calcium Content, Calcium Balance and Mode of Uptake in a Subterranean Mammal, the Damara Mole-Rat¹

Tammy Pitcher, Rochelle Buffenstein, James D. Keegan^*, Gopal P. Moodley and Shlomo Yahav

^* Physiology Department, Medical School; Department of General Physiology, Dental School; Medical Research Council Mineral Metabolism Research Unit, Department of Paediatrics, Baragwanath Hospital, University of the Witwatersrand, Johannesburg, Republic of South Africa

Calcium flux and mode of uptake were investigated in an underground dwelling mole-rat, Cryptomys damarensis, fed diets of varying Ca content. The amount of dietary Ca positively influenced the amounts ingested, absorbed and retained. The linear relationship between ingested and absorbed Ca was significantly (P < 0.001) correlated, implying that this process is nonsaturable. When mole-rats were fed a diet low in Ca, apparent fractional absorption of Ca was high (85.88%). This increased still further when the diet was changed to a food of greater Ca content (96.13%, carrots; 96.97%, gemsbok cucumber). Mineral homeostasis is regulated at the intestinal level in most mammals. Regardless of dietary Ca content, uptake of ⁴⁵Ca (examined via the everted gut sac technique) was passive, confirming that absorption is via a nonsaturable process. Plasma Ca concentrations were not tightly regulated, yet when fed the diet with the highest Ca content, mole-rats were not hypercalcemic. Regardless of diets, Ca apparent fractional retention was positive, and approached physiological maxima (>97%). Cryptomys damarensis, in using highly efficient modes of mineral uptake and retention, is therefore capable of fully exploiting the limited food resources of their arid ecotope.

KEY WORDS: • mole-rats • calcium balance • calcium absorption

¹ Supported by financial assistance from the Medical Research Council to R. Buffenstein, which is gratefully acknowledged.

Manuscript received 2 August 1990. Revision accepted 13 May 1991.