Effects of vitamin D-3, 17 beta-estradiol, vasoactive intestinal peptide, and glutamate on electric coupling between rat osteoblast-like cells in vitro

Osteoblast-like cells express receptors for various hormones and neurotrans mitters that induce widespread actions in the bone to which intercellular c ommunication and its modulation may contribute, Therefore, we examined the effects of the osteotropic hormones vitamin D-3 (vitD(3)) and 17 beta-estra diol (17 beta-E-2) as well as the neurotransmitter vasoactive intestinal pe ptide (VIP) and the excitatory amino acid glutamate (Glu) on gap junctions between rat osteoblast-like (ROB) cells in vitro. Electric coupling was mea sured by simultaneous intracellular recordings from neighboring cells. The coupling factor (c(f)) was calculated from membrane potential changes induc ed by alternate current injections into both cells. In ROB cells c(f) was i ncreased by 5 x 10(-8) mol/L vitD(3) to 130 +/- 13% (mean +/- SD; n = 6) of the initial value within 5-20 min. This effect was not reversible after wa shing with control saline for 10-15 min, In six cell pairs, c(f) was not af fected by vitD(3) (94 +/- 5%), In three cell pairs superfusion of 10(-8) mo l/L E-2 reduced c(f) to 80 +/- 6% within 10 min, whereas, in two cell pairs , this hormone improved c(f) to 140% within 20 min. Exposure of VIP (3.10(- 8) mol/L) did not alter c(f) in the majority of cells (99 +/- 3%; n = 11), In five cell pairs, c(f) was improved within 5-15 min to 133 +/- 12%, where as, in one cell pair, c(f) was reduced to 22% by VIP. In contrast, brief ap plication of Glu (5.10(-3) mol/L) decreased c(f) to 75 +/- 5% (n = 5), wher eas, in nine other cell pairs, c(f) was not affected (96 +/- 5%), The findi ngs indicate that cell-cell coupling of gap junctions between bone cells ca n be altered by actions of hormones and transmitters in a cell-pair-specifi c way, which may depend on their functional state. (Bone 23:521-526; 1998) (C) 1998 by Elsevier Science Inc. All rights reserved.