Pressure-clamp: a method for rapid step perturbation of mechanosensitive channels

Here we describe a pressure-clamp method for applying suction or pressure steps to membrane patches in order to study the activation, adaptation and relaxation characteristics of mechanosensitive (MS) channels. A description is given of the mechanical arrangement of the pressure clamp which involves a balance between negative (suction) and positive pressures. The electronic circuitry of the feedback control is described. We also describe the optimal time response (≈ 10 ms) of the pressure-clamp, the amplitude of pressure resolution (0.2-0.5 mmHg; 27-67 Pa) and the factors influencing these parameters. We illustrate the applications of the clamp on the Xenopus oocyte and cultured skeletal myotubes from dystrophic mouse (mdx) muscle, both of which express MS channels. Studies with pressure/suction pulses indicate that in both muscle and oocytes MS channel activity displays adaptation. The ability to study current relaxations following step changes in pressure/suction using the pressure-clamp in combination with patch-clamp techniques provides the opportunity for analysis of the time, voltage and pressure dependence of the opening and closing of MS channels.