AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 3 290-R295, Copyright © 1985 by American Physiological Society
Annual and diurnal patterns of plasma calcium fractions in anuran Rana pipiens
D. R. Robertson
Ionized calcium [Ca2+] in the amphibian Rana pipiens was measured over 18
mo. An annual variation about the mean of 1.10 mmol/l was observed that
peaked in April (1.36 mmol/l) and attained minimal levels in October (0.84
mmol/l). Plasma total calcium [Ca]t, plasma proteins, and the bound calcium
fraction also exhibited annual oscillations. The annual mean binding
capacity of plasma proteins for calcium was established at 0.0175 mmol/g.
Of the plasma total calcium in spring animals, nonprotein-bound calcium
complexes [Ca]c were less than 3% of the total whereas 80% was composed of
[Ca2+] and 17% as protein-bound calcium [Ca]pb. In autumn [Ca2+] composed
40%, [Ca]pb 30%, and [Ca]c 30% of plasma total calcium. An equilibrium
exists between [Ca2+] and [Ca]c, which maintains a combined annual mean of
1.48 mmol/l calcium. Diurnal variations superimposed on the annual cycles
are modulated by apparent movement of plasma water and an intrinsic 12-h
rhythm for [Ca2+]. No definite associations could be made with the
entrainment of specific rhythms of the three calcium fractions with the
light-dark cycle.
