Effects of changes of intracellular pH on contraction in XXXX cardiac Purkinje fibers.

@entity8777 @entity5838 @entity742 @entity515 @entity520 @entity66783
Intracellular pH (pHi) was measured with a pH-sensitive microelectrode in voltage-clamped @entity742 cardiac Purkinje fibers while tension was simultaneously measured. All solutions were nominally @entity515 /HCO3 free and were buffered with Tris. The addition of @entity8777 (5-20 mM) produced an @entity5838 that was associated with an increase of twitch tension. At the same time, a component of voltage-dependent tonic tension developed. Prolonged exposure (greater than 5 min) to @entity8777 resulted in a slow recovery of pHi accompanied by a decrease of tension. Removal of @entity8777 produced a transient @entity520 that was accompanied by a fall of force. In some experiments, there was then a transient recovery of force. If extracellular pH (pHo) was decreased, then pHi decreased slowly. Tension also fell slowly. An increase of pHo produced a corresponding increase of both force and pHi. The application of @entity66783 (10 microM) increased force and produced an intracellular @entity520 . The addition of @entity8777 , to remove this @entity520 partially, produced a significant increase of force. The above results show that contraction is sensitive to changes of intracellular but not extracellular pH. This pH dependence will therefore modify the contractile response to inotropic maneuvers that also affect pHi.
