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An unconventional approach to studying ion channel kinetics is exploited. Here we describe the effects of a periodically varying membrane potential on the open-closed transitions of single K+ channels. The use of cycle histograms allows one to measure the transition probabilities as functions of the stimulus phase. The results show that such probabilities vary with the stimulation frequency and with the stimulus history, thus highlighting a dynamic aspect in the switching of this ion channel.

Here we resume the results of applying periodic forcing to a single ion channel. This approach, whose main aim was to test the existence of dynamical components in the channel switching, allowed us a direct evaluation of the rate constants of the channel transitions and showed a trend which is in keeping with stochastic resonance.

BACKGROUND: The safety of human serum albumin (HSA) is of special interest with respect to virus transmission because of the wide use of this blood product as a therapeutic agent and also, added to other products, as an excipient or a stabilizer. Conflicting data are reported concerning HSA contamination by small, naked viruses such as the erythrovirus B19 (B19V) and the anellovirus torquetenovirus (TTV). This study has been performed to assess the effect of the HSA purification procedures on the viral contamination. STUDY DESIGN AND METHODS: Known concentrations of B19V and TTV virus were spiked in raw Fraction V, the starting material from fractionated human plasma for HSA purification, which was subsequently submitted to the depth filtration procedure. After spiking, B19V and TTV genome copies were determined by real-time quantitative polymerase chain reaction assays in the mixture at the end of Fraction V dissolution, to determine the virus concentration achieved, in the HSA solution after the filtration step, in the filtered postwashing fluid, and in the supernatant of resuspended Celite. RESULTS: B19V was completely adsorbed by the Celite used as a filter aid in the depth filtration process and was thus undetectable in the resulting HSA-containing fraction. In contrast, in 2 out of 3 experiments, TTV was detected in all samples. CONCLUSION: The different behavior of the two viruses might be a reflection of their different surface charge.

The voltage dependence of stretch-activated cation channels in leech central neurons was studied in cell-free configurations of the patch-clamp technique. We established that stretch-activated channels excised from identified cell bodies of desheathed ganglia, as well as from neurons in culture, were slowly and reversibly activated by depolarizing membrane potentials. Negative pressure stimuli, applied to the patch pipette during a slow periodical modulation of membrane potential, enhanced channel activity, whereas positive pressures depressed it. Voltage-induced channel activation was observed, with soft glass pipettes, both in inside-out and outside-out membrane patches, at negative and positive reference potentials, respectively. The results presented in this study demonstrate that membrane depolarization induces slow activation of stretch-activated channels of leech central neurons. This phenomenon is similar to that found in Xenopus oocytes, however, some peculiar features of the voltage dependence in leech stretch-activated channels indicate that specific membrane-glass interactions might not necessarily be involved. Moreover, following depolarization, stretch-activated channels in membrane patches from neurons in culture exhibited significantly shorter delay to activation (sec) than their counterparts from neurons of freshly isolated ganglia (hundreds of sec).