Figure 3. Stretch-induced ET-1 secretion is dependent on extracellular calcium.

Panel A shows that adult astrocyte SACs can conduct Ca²⁺ in response to mechanical stress. An outside-out patch was exposed to 500 millisecond pressure pulses (100 mmHg as noted with the horizontal bar) with 1.5 seconds between pulses. The holding potential was −50 mV and a downward deflection denotes Ca²⁺ influx. Panel B shows ET-1 concentration measured in media following a 24-hour sinusoidal stretching regimen (squares, 0.1 Hz, 20% linear strain) and in unstretched control cultures (triangles). Extracellular Ca²⁺ levels in the media were lowered by buffering with NTA. The curve is a fit of the data to a 2-parameter function (see Supplementary Material for derivation): Y= P1*ln[Ca²⁺]_out + P2 − 42.26, P1=16.06 ± 0.3, P2 = 152.7 ± 0.5.