Activation and inactivation of mechanosensitive currents in the chick heart

The behavior of MS channels in embryonic chick ventricular myocytes activat ed by direct mechanical stimulation is strongly affected by inactivation. T he amplitude of the current is dependent not only on the amplitude of the s timulus, but also the history of stimulation. The MS current inactivation a ppears to be composed of at least two contributions: (i) rearrangement of t he cortical tension transducing elements and (ii) blocking action of an aut ocrine agent released from the cell. With discrete mechanical stimuli, the MS current amplitude in the second pr ess of a double press protocol was always smaller than the amplitude of the first MS current. Occasionally, a large MS current occurred when the cell was first stimulated, but subsequently the cell became unresponsive. For a series of stimuli of varying amplitudes, the order in which they were appli ed to the cell affected the size of the observed MS current for a given sti mulus magnitude. When continuous sinusoidal stimulation was applied to the cells, the MS cur rent envelope either reached a steady stare, or inactivated. With sinusoida l stimulation, the MS response could be enhanced or restored by simple perf usion of fluid across the cell. This suggests that mechanical stimulation o f the cells produces an autocrine inhibitor of MS channels as well as resul ting in cortical rearrangement.