Membrane stretch activates a high-conductance K+ channel in G292 osteoblastic-like cells

Summary A high-conductance K⁺-selective ion channel was studied in excised membrane patches from human G292 osteoblast-like osteosarcoma cells. Channel conductance averaged 170 pS in symmetric solutions of 153mm KCl, and 135 pS when the pipette was filled with standard saline (150mm NaCl). The probability of the channel being in an open state (P _open) increased with membrane potential, internal calcium, and applied negative pressure. At pCa7, channel activity was observed at membrane potentials greater than 60 mV, while at pCa3, channel activity was seen at 10 mV. Likewise, in the absence of applied pressure, channel openings were rare (P _open = 0.02), whereas with –3 cm Hg applied pressure,P _open increased to 0.40. In each case, i.e., voltage, calcium concentration, and pressure, the increase inP _open resulted from a decrease in the duration of long-closed (interburst) intervals and an increase in the duration of long-open (burst) intervals. Whole-cell responses were consistent with these findings. Hypotonic shock produced an increase in the amplitude and conductance of the outward macroscopic current and a decrease in its rise time, and both single-channel and whole-cell currents were blocked by barium. It is suggested that the voltage-gated, calcium dependent maxi-K⁺ channel in G292 osteoblastic cells is sensitive to membrane stretch and may be directly involved in osmoregulation of these cells. Further, stretch sensitivity o£ the maxi-K⁺ channel in osteotrophic cells may represent an adaptation to stresses associated with mechanical loading of mineralized tissues.