Rita Canella

The slow Ca(2+)-activated K+ current, IAHP, in the rat sympathetic neurone.

1. Adult and intact sympathetic neurones of the rat superior cervical ganglion maintained in vitro at 37 degrees C were analysed using the two‐electrode voltage‐clamp technique in order to investigate the slow component of the Ca(2+)‐dependent K+ current, IAHP. 2. The relationship between the after‐hyperpolarization (AHP) conductance, gAHP, and estimated Ca2+ influx resulting from short‐duration calcium currents evoked at various voltages proved to be linear over a wide range of injected Ca2+ charge. An inflow of about 1.7 x 10(7) Ca2+ ions was required before significant activation of gAHP occurred. After priming, the gAHP sensitivity was about 0.3 nS pC‐1 of Ca2+ inward charge. 3. IAHP was repeatedly measured at different membrane potentials; its amplitude decreased linearly with membrane hyperpolarization and was mostly abolished close to the K+ reversal potential, EK (‐93 mV). The monoexponential decay rate of IAHP was a linear function of total Ca2+ entry and was not significantly altered by membrane potential in the ‐40 to ‐80 mV range. 4. Voltage‐clamp tracings of IAHP could be modelled as a difference between two exponentials with tau on approximately 5 ms and tau off = 50‐250 ms. 5. Sympathetic neurones discharged only once at the onset of a long‐lasting depolarizing step. If IAHP was selectively blocked by apamin or D‐tubocurarine treatments, accommodation was abolished and an unusual repetitive firing appeared. 6. Summation of IAHP was demonstrated under voltage‐clamp conditions when the depolarizing steps were repeated sufficiently close to one another. Under current‐clamp conditions the threshold depolarizing charge for action potential discharge significantly increased with progressive pulse numbers in the train, suggesting that an opposing conductance was accumulating with repetitive firing. This frequency‐dependent spike firing ability was eliminated by pharmacological inhibition of the slow IAHP. 7. The IAHP was significantly activated by a single action potential; it was turned on cumulatively by Ca2+ load during successive action potential discharge and acted to further limit cell excitability.

Isonymy in emigrants from Ferrara in 1981–1988

The distribution of surnames in the emigrants from the population of the town of Ferrara in the period 1981-88 was studied by sex and place of birth, namely Ferrara versus other places. Emigrants born in Ferrara were defined as first time emigrants and those who had previously immigrated to Ferrara were defined second time emigrants. It was found that random isonymy is smaller in second time emigrants. Sex ratio is not different in the two types of emigrants. As indicators of the abundance of surnames in a distribution, the common ecological indexes derived from entropy were used and compared between types of emigrants. It was found that redundancy, as isonymy, is larger in the first time emigrants than in second time emigrants. It was observed that second time emigrants were consistently and significantly older than first time emigrants, and that a considerable fraction of them, (22.4%) returned to their place of birth. A sexual dimorphism in age at emigration was observed in second time emigrants, females emigrating at an older age than males.

Isonymy in records of births and deaths in Ferrara

Surname distributions were studied in records of male and female births in Ferrara in the period 1982-89, and in records of male and female deaths in the same period. Average year of birth and standard deviation was 1985 +/- 2.3 for the birth series, and 1912 +/- 14.4 for the death series. Then the surname distributions, in two independent samples at an average distance of 73 years, were compared. It was observed that random isonymy within series, which depends on the shape of the distribution, stays fairly constant at three generations of distance, indicating near-equilibrium of surname turnover. The migrational contribution is indicated by the significant decrease of random isonymy between series, measured with the method of Lasker. It was also observed that immigrants to Ferrara have a life-span significantly longer than people born in the town.

A model of signal processing at a mammalian sympathetic neurone.

A computational model has been developed for the action potential and, more generally, the electrical behaviour of the rat sympathetic neurone. The neurone is simulated as a complex system in which five voltage-dependent conductances (gNa, gCa, gKV, gA, gKCa), one Ca2+-dependent voltage-independent conductance (gAHP) and the activating synaptic conductance coexist. The individual currents are mathematically described, based on a systematic analysis obtained for the first time in a mature and intact mammalian neurone using two-electrode voltage-clamp experiments. The simulation initiates by setting the starting values of each variable and by evaluating the holding current required to maintain the imposed membrane potential level. It is then possible to simulate current injection to reproduce either the experimental direct stimulation of the neurone or the physiological activation by the synaptic current flow. The subthreshold behaviour and the spiking activity, even during long-lasting current application, can be analysed. At every time step, the program calculates the amplitude of the individual currents and the ensuing changes; it also takes into account the accompanying K+ accumulation process in the perineuronal space and changes in Ca2+ load. It is shown that the computed time course of membrane potential must be filtered, in order to reproduce the limited bandwidth of the recording instruments, if it is to be compared with experimental measurements under current-clamp conditions. The membrane potential trajectory and single current data are written in files readable by graphic software. Finally, a screen image is obtained which displays in separate graphs the membrane potential time course, the synaptic current and the six ionic current flows. The simulated action potentials are comparable to the experimental ones as concerns overshoot amplitude and rising and falling rates. Therefore, this program is potentially helpful in investigating many aspects of neurone behaviour.

Reproductive behaviour of families segregating for Cooley's anaemia before and after the availability of prenatal diagnosis.

The reproductive behaviour of couples with heterozygous beta thalassaemia, with at least one affected child, was investigated for the period 1955 to 1984 and was compared to the behaviour of control couples matched for age, age at marriage, and presence of at least one child. The comparisons were made as a function of knowledge of the risk and availability of prenatal diagnosis and abortion. It was found that the couples segregating for Cooleys anaemia, before knowledge of the risk, had a higher reproductive rate than that of control couples. Knowledge of the genetic risk had a different effect on reproductive behaviour in the 1950s from that in later years. The difference was attributed both to the influence of cultural factors and to technical, therapeutic, and diagnostic advances.

Ionic currents in hair cells dissociated from frog semicircular canals after preconditioning under microgravity conditions

The effects of microgravity on the biophysical properties of frog labyrinthine hair cells have been examined by analyzing calcium and potassium currents in isolated cells by the patch-clamp technique. The entire, anesthetized frog was exposed to vector-free gravity in a random positioning machine (RPM) and the functional modification induced on single hair cells, dissected from the crista ampullaris, were subsequently studied in vitro. The major targets of microgravity exposure were the calcium/potassium current system and the kinetic mechanism of the fast transient potassium current, I(A). The amplitude of I(Ca) was significantly reduced in microgravity-conditioned cells. The delayed current, I(KD) (a complex of I(KV) and I(KCa)), was drastically reduced, mostly in its I(KCa) component. Microgravity also affected I(KD) kinetics by shifting the steady-state inactivation curve toward negative potentials and increasing the sensitivity of inactivation removal to voltage. As concerns the I(A), the I-V and steady-state inactivation curves were indistinguishable under normogravity or microgravity conditions; conversely, I(A) decay systematically displayed a two-exponential time course and longer time constants in microgravity, thus potentially providing a larger K(+) charge; furthermore, I(A) inactivation removal at -70 mV was slowed down. Stimulation in the RPM machine under normogravity conditions resulted in minor effects on I(KD) and, occasionally, incomplete I(A) inactivation at -40 mV. Reduced calcium influx and increased K(+) repolarizing charge, to variable extents depending on the history of membrane potential, constitute a likely cause for the failure in the afferent mEPSP discharge at the cytoneural junction observed in the intact labyrinth after microgravity conditioning.

Modulation of Chloride Currents in Human Lung Epithelial Cells Exposed to Exogenous Oxidative Stress

Air pollution continues to be a major public health concern affecting 9 out of 10 individuals living in urban areas worldwide. Respiratory tract is the organ most exposed to gas pollution, and ozone has been shown to be one of the most noxious pollutants to which living organisms are exposed. In the present work, we have investigated the effects of 0.1 ppm of ozone on chloride currents in human lung epithelial cells (A549 line) and whether this effect could be modulated by vitamin E pre‐treatment. Whole‐cell patch clamp technique was applied to not excitable cells in order to obtain information about chloride currents behavior, important for epithelial lung cells homeostasis. Significant alteration of the I–V curve after ozone treatment was observed, with the appearance of a large outward rectifier component decreasing over time and returning to the basal state levels after 24 h. Statistical analysis indicated a modification of the amount of ions passing the membrane in the unit of time as a possible cause of this difference. RT‐qPCR analysis showed an increase in ClC‐2 and ORCC mRNA after ozone exposure. In addition, pre‐treatment with vitamin E was able to suppress the outward rectifier component induced by ozone, bringing back the current values to the control level and preventing ozone induced chloride channels up regulation. Our data suggest that ozone exposure is able to modify chloride current density and the use of vitamin E can prevent the above‐mentioned damage. J. Cell. Physiol. 232: 1817–1825, 2017.

The Amplitude and Inactivation Properties of the Delayed Potassium Currents Are Regulated by Protein Kinase Activity in Hair Cells of the Frog Semicircular Canals

In hair cells dissected from the frog crista ampullaris, the combination of a calcium-dependent (IKCa) and a purely voltage-dependent component (IKV) gives rise to the delayed potassium current complex (IKD). These currents have been recently reported to display slow depolarization-induced inactivation and biphasic inactivation removal by hyperpolarization. The amplitude and inactivation kinetics of both IKCa and IKV are drastically modulated by a previously unrecognized mechanism of protein phosphorylation (sensitive to kinase inhibitors H89 and KT5823), which does not interfere with the transient potassium current (IA) or the calcium current (ICa). IKD amplitude was stable in cells patched with pipettes containing 8 mM ATP or under perforated-patch; under these conditions, a 10 min treatment with 10 µM H89 or 1–10 µM KT5823 reduced IKD amplitude by a mean of 67% at +40 mV. Similarly affected was the isolated IKV component (ICa blocked with Cd2+). Thus, a large potassium conductance can be activated by depolarization, but it is made available to the cell to a variable extent that depends on membrane potential and protein kinase activity. The total gKD ranged 4.6–44.0 nS in control cells, according to the level of steady-state inactivation, and was reduced to 1.4–2.7 nS after protein kinase inhibition. When sinusoidal membrane potential changes in the −70/−10 mV range were applied, to mimic receptor response to hair bundle deflection, IKD proved the main current dynamically activated and the only one regulated by PK: H89 decreased the total outward charge during each cycle by 60%. Phosphorylation appears to control both the amount of IKCa and IKV conductance activated by depolarization and the fraction thereof which can be rescued by removal of inactivation. The balance between the depolarizing transduction current and the repolarizing potassium current, and eventually the transmitter release at the cytoneural junction, are therefore modulated by a phosphorylation-mediated process.

Sensory transduction at the frog semicircular canal: how hair cell membrane potential controls junctional transmission

At the frog semicircular canals, the afferent fibers display high spontaneous activity (mEPSPs), due to transmitter release from hair cells. mEPSP and spike frequencies are modulated by stimulation that activates the hair cell receptor conductance. The relation between receptor current and transmitter release cannot be studied at the intact semicircular canal. To circumvent the problem, we combined patch-clamp recordings at the isolated hair cell and electrophysiological recordings at the cytoneural junction in the intact preparation. At isolated hair cells, the K channel blocker tetraethylammonium (TEA) is shown to block a fraction of total voltage-dependent K-conductance (IKD) that depends on TEA concentration but not on membrane potential (Vm). Considering the bioelectric properties of the hair cell, as previously characterized by this lab, a fixed fractional block of IKD is shown to induce a relatively fixed shift in Vm, provided it lies in the range −30 to −10 mV. The same concentrations of TEA were applied to the intact labyrinth while recording from single afferent fibers of the posterior canal, at rest and during mechanical stimulation. At the peak of stimulation, TEA produced increases in mEPSP rate that were linearly related to the shifts produced by the same TEA concentrations (0.1–3 mM) in hair cell Vm (0.7–5 mV), with a slope of 29.8 Hz/mV. The membrane potential of the hair cell is not linearly related to receptor conductance, so that the slope of quantal release vs. receptor conductance depends on the prevailing Vm (19.8 Hz/nS at −20 mV; 11 Hz/nS at −10 mV). Changes in mEPSP peak size were negligible at rest as well as during stimulation. Since ample spatial summation of mEPSPs occurs at the afferent terminal and threshold-governed spike firing is intrinsically nonlinear, the observed increases in mEPSP frequency, though not very large, may suffice to trigger afferent spike discharge.

KINSHIP STRUCTURES AND MIGRATION IN THE PO-DELTA

The kinship analysis of seven genetic systems in the province of Ferrara permits some considerations on the possible chronology of emergence of their polymorphisms in the area. It is proposed that, assuming neutrality of these systems, and under several restrictions, the emergence by migration of the polymorphisms in the seven systems ACP, ESD, GLO, GPT, PGD, PGM1; PGP might have had the following sequence: PGP and GLO and possibly PGD; PGMj and GPT; ACP and ESD. All polymorphisms must be older than the β‐thalassemia polymorphism in the area.