Figure 1.

Stretch-dependent hyperpolarization and inhibition of AP complexes in the murine colon. (A) Membrane potential and superimposed AP complexes of the circular muscle layer, before, during and after application of a muscle stretch ramp that was delivered at 6 μm s⁻¹ until a 5 mN isometric force was reached. (B) Isometric force measurement during applied ramp indicated by the arrows. (C) Stretch ramp applied at a constant rate of 6.0 μm s⁻¹ until 5 mN was reached. The rate of force application was 0.156 mN s⁻¹ and the duration of the active portion of the ramp 320 seconds. Membrane hyperpolarization, indicated by the dashed line in A, and loss of AP complexes occurred during the active change in muscle length. Recovery of membrane potential and return of AP complexes occurred following termination of the active length ramp while muscle length was maintained. Recovery of the change in muscle length often produced a rebound depolarization and an increase in AP discharge for 1–3 cycles before electrical and mechanical activity returned to pre-stretch control activity. (D–F) Effect of repetitive colonic stretch on membrane potential and AP complex discharge. (D & E) Membrane potential and isometric force in response to three rapid stretch applications delivered at 31μm s⁻¹ until an isometric force of 5 mN was reached (arrows in D). Repetitive stretching of the colon (F) caused a reproducible hyperpolarization in membrane potential (dashed lines in D) and inhibition of AP complexes.