AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 4 655-R660, Copyright © 1987 by American Physiological Society
Calcium content of frog sciatic nerve during chronic hypocalcemia and hypercalcemia
K. C. Wadhwani, H. Levitan and S. I. Rapoport
Laboratory of Neurosciences, National Institute on Aging, Bethesda, Maryland 20892.
We examined the calcium contents of desheathed peripheral nerve,
perineurial sheath, and whole sciatic nerve in the frog as a function of
the steady-state plasma concentration of ionized calcium. Chronic
hypocalcemia was induced by parathyroidectomy and by bathing frogs in a
phosphate medium. Chronic hypercalcemia was induced by administering
vitamin D3 and by bathing frogs for up to 2 wk in medium containing 50 mM
CaCl2. Calcium was measured with a calcium-sensitive electrode and by
atomic absorption spectroscopy. The calcium contents (mmol/kg wet wt) in
whole nerve, desheathed nerve, and the perineurial sheath varied linearly
with slopes of 0.72, 0.71, and 1.72, respectively, with plasma
concentration (mM) of ionized calcium, which ranged from 0.3 to 8.0 mM. In
the same animals the calcium content in the cerebrum was independent of
plasma calcium between 0.5 and 1.5 mM but rose at higher plasma
concentrations. Our results indicate that net calcium concentration in the
frog peripheral nerve is not regulated during chronic hypocalcemia and
hypercalcemia, whereas brain calcium is regulated at plasma calcium
concentrations less than 1.5 mM. The lack of calcium regulation in the
nerve is attributed to the lack of calcium regulation in the endoneurial
compartment.
