Purkinje shift

The subjectivity of history-taking as yet has not been overcome by any objective field test of night blindness that is applicable in young children, in spite of many attempts to develop suitable instruments or procedures. A simple rapid test based on the Purkinje shift from cone to rod vision first suggested by Thornton (1977) has been adapted to adults by Vinton and Russell (1981) and is now being tested for its feasibility, specificity, and sensitivity among children (N. Solomons, 1982, personal communication). 

B.aman In whole cell recordings from Purkinje cells over time, the inactivation curve tends to shift to more negative voltages. 

Following hypo-osmotic stress there is a transient shift of taurine from the Purkinje cells to the Bergmann glial compartment, where taurine-immunoreactivity now becomes apparent (Nagelhus et al., 1993). 

By increasing the rates of ventricular contraction and relaxation, Epi preferentially shortens systole and usually does not reduce the duration of diastole. Epi speeds the heart by accelerating the slow depolarization of sinoatrial (SA) nodal cells that takes place during phase 4 of the action potential (see Chapter 34). The amplitude of the AP and the maximal rate of depolarization (phased) also are increased. A shift in the location of the pacemaker within the SA node often occurs, owing to activation of latent pacemaker cells. In Purkinje fibers, Epi accelerates diastolic depolarization and may activate latent pacemakers. If large doses of Epi are given, premature ventricular contractions occur and may herald more serious ventricular arrhythmias. Conduction through the Purkinje system depends on the level of membrane potential at the time of excitation. Epi often increases the membrane potential and improves conduction in Purkinje fibers that have been excessively depolarized. 

Effects on cardiac excitability may be based on blocking effects of Cd on ion channels, e.g. voltage-dependent calcium channels (see [199] for a review) or Na channels of Purkinje fibres [350]. Cd may also increase outward potassium currents of ventricular myocytes and shift their voltage dependency of activation to more positive voltages [351], or interfere with Ca-dependent processes in the heart [352]. 

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