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

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 153 mm KCl, and ∼135 pS when the pipette was filled with standard saline (150 mm 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 in P_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.