Effects of vitamin D3, 17β-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 neurotransmitters that induce widespread actions in the bone to which intercellular communication and its modulation may contribute. Therefore, we examined the effects of the osteotropic hormones vitamin D3 (vitD3) and 17β-estradiol (17β-E2) as well as the neurotransmitter vasoactive intestinal peptide (VIP) and the excitatory amino acid glutamate (Glu) on gap junctions between rat osteoblast-like (ROB) cells in vitro. Electric coupling was measured by simultaneous intracellular recordings from neighboring cells. The coupling factor (cf) was calculated from membrane potential changes induced by alternate current injections into both cells. In ROB cells cf was increased by 5 × 10−8 mol/L vitD3 to 130 ± 13% (mean ± SD; n = 6) of the initial value within 5–20 min. This effect was not reversible after washing with control saline for 10–15 min. In six cell pairs, cf was not affected by vitD3 (94 ± 5%). In three cell pairs superfusion of 10−8 mol/L E2 reduced cf to 80 ± 6% within 10 min, whereas, in two cell pairs, this hormone improved cf to 140% within 20 min. Exposure of VIP (3 • 10−8 mol/L) did not alter cf in the majority of cells (99 ± 3%; n = 11). In five cell pairs, cf was improved within 5–15 min to 133 ± 12%, whereas, in one cell pair, cf was reduced to 22% by VIP. In contrast, brief application of Glu (5 • 10−3 mol/L) decreased cf to 75 ± 5% (n = 5), whereas, in nine other cell pairs, cf was not affected (96 ± 5%). The findings indicate that cell-cell coupling of gap junctions between bone cells can be altered by actions of hormones and transmitters in a cell-pair-specific way, which may depend on their functional state.