Differential depolarization-activated calcium responses in fetal and neonatal rat osteoblast-like cells.
The present study evaluates differential occurrence of voltage-dependent calcium channels (VDCC) in the membranes of fetal (FROB) and neonatal (NROB) calvarian rat osteoblastic cells in primary culture. The intracellular calcium concentration ([Ca2+]i) was monitored upon depolarization of the cell membrane with the use of high K+ containing extracellular solutions. [Ca2+]i was measured in populations of cells as well as in individual cells using Fura-2, whereas the membrane potential (Em) was recorded in parallel experiments using patch-clamp techniques. Increasing the extracellular K+ concentration resulted in an instantaneous depolarization of Em of both FROB and NROB. This depolarization of Em did not significantly affect [Ca2+]i of populations of FROB and neonatal osteoblast precursors (NpROB). In contrast to FROB and NpROB, NROB populations responded to depolarization with significant transient [Ca2+]i increases that could be blocked by the calcium antagonist verapamil and were absent if extracellular Na+ was replaced for choline instead of K+. In individual cell measurements, response frequencies as well as the magnitude of [Ca2+]i responses upon depolarization of NROB were much higher than those of FROB, suggesting that more NROB than FROB possess VDCC. This phenomenon might point to a development-related expression of VDCC in the membranes of osteoblast-like cells.
Wiltink
A
A
Department of Physiology and Physiological Physics, Leiden University, The Netherlands.
Van Duijn
B
B
Weidema
A F
AF
De Vos
A
A
van der Meer
J M
JM
Nijweide
P J
PJ
Ypey
D L
DL
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005333:Fetus; D016257:Fura-2; D008564:Membrane Potentials; D010006:Osteoblasts / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D013050:Spectrometry, Fluorescence
D015220:Calcium Channels; D011188:Potassium; D002118:Calcium; D016257:Fura-2