Osteoblasts possess both receptors and ion channels which are presumed targets for hormones, local mediators and mechanical influences. The functions of these receptors and ion channels must include regulation of cell proliferation and secretion, processes which are critical to bone remodelling. In bone tissue however such receptors and ion channels are relatively poorly characterised. electrophysiologically Whole cell measurements have shown the presence of NMDA receptors in primary rat osteoblasts (Gu et al. 2002) and K currents in MG63 human osteoblast-like cells or human osteogenic precursor cells (Yellowley et al. 1998; Weskamp et al. 2000). Few single channel measurements exist in these cells.

We have carried out single channel patch-clamp experiments in human MG63 osteoblast-like cells. RT-PCR showed that members of the TRP channel family (TRPM4b) and maxi-K channels were expressed in these cells. Cells with a fibroblastic appearance were selected for study. The bathing solution was mM: 150 NaCl; 3 KCl; 2 MgCl₂; 2 CaCl₂; 10 Hepes; 10 Glucose, pH 7.4. The recording pipette contained in mM: 140 KCl; 5 NaCl; 1 MgCl₂; 1 CaCl₂; EGTA 11; Hepes 10, pH 7.2. Giga-ohm seals (2-10 GV resistance) were formed in about 50 % of cases (n = 155 patches).

A number of single channel currents were observed in cell-attached recordings. A large conductance channel was present in almost every patch. The open probability (Po) was voltage-dependent increasing on depolarisation. There were up to seven active channels in a patch at positive potentials. The I-V relationship was linear up to140 mV depolarised (the mean conductance was 227 ± 41 pS (n = 15) thereafter drooping charactistically. The Po-voltage curve showed hysteresis, the activity of the channel being higher after depolarisation. The channel was activated by bath application of 10-4 M glutamate (Mg²⁺-free Locke). This channel was also present in excised inside-out and outside-out patches ( asymmetric K, n = 14), and was sensitive to both internal and external TEA (2 mM and 500 µM respectively). A proportion of patches also had another channel at resting potential and hyperpolarised voltages. This channel had a linear current-voltage relationship and a slope conductance of 54 pS (n = 8). There were up to six active channels in the patch. In a small percentage of patches ( n = 5) there was a large conductance (> 200 pS), high density, stretch-activated channel highly active at the resting potential.

†I. Prajerová is an Erasmus Exchange Student.