A. Wiltink et al., DIFFERENTIAL DEPOLARIZATION-ACTIVATED CALCIUM RESPONSES IN FETAL AND NEONATAL RAT OSTEOBLAST-LIKE CELLS, Calcified tissue international, 54(4), 1994, pp. 278-283
The present study evaluates differential occurrence of voltage-depende
nt calcium channels (VDCC) in the membranes of fetal (FROB) and neonat
al (NROB) calvarian rat osteoblastic cells in primary culture. The int
racellular calcium concentration ([Ca2+]i) was monitored upon depolari
zation of the cell membrane with the use of high K+ containing extrace
llular solutions. [Ca2+]i was measured in populations of cells as well
as in individual cells using Fura-2, whereas the membrane potential (
E(m)) was recorded in parallel experiments using patch-clamp technique
s. Increasing the extracellular K+ concentration resulted in an instan
taneous depolarization of E(m) of both FROB and NROB. This depolarizat
ion of E(m) did not significantly affect [Ca2+]i of populations of FRO
B and neonatal osteoblast precursors (NpROB). In contrast to FROB and
NpROB, NROB populations responded to depolarization with significant t
ransient [Ca2+]i increases that could be blocked by the calcium antago
nist verapamil and were absent if extracellular Na+ was replaced for c
holine instead of K+. In individual cell measurements, response freque
ncies as well as the magnitude of [Ca2+]i responses upon depolarizatio
n of NROB were much higher than those of FROB, suggesting that more NR
OB than FROB possess VDCC. This phenomenon might point to a developmen
t-related expression of VDCC in the membranes of osteoblast-like cells
.