[Warning about risk of invasive infections in splenectomized patients. Experiences from University Hospital Brno, Czech Republic, in 2011]. / Upozornení na nebezpecí invazivních infekcí u splenektomovaných pacientu. Zkusenosti z FN Brno 2011.

Syndrome of fulminant sepsis in splenectomized (overwhelming postsplenectomy infection - OPSI) is feared and often fatal infectious complication in patients after splenectomy. The risk of syndrome of fulminant sepsis in splenectomized in these persons persists lifelong and doesn't diminish during the time. Etiologically, encapsulated bacterias like Streptococcus pneumoniae, Haemophilus influenzae group b and Neisseria meningitidis are involved. As the mortality of syndrome of fulminant sepsis in splenectomized is very high, it is indispensable to educate and vaccinate persons in risk. The authors present case reports of three splenectomized patients who were hospitalized for invasive pneumococcal infection in the University Hospital Brno, Czech Republic, in 2011.

[The effect of patient's body weight, gender and baseline viral load on the efficacy of hepatitis C therapy]. / Ovlivnení uspesnosti lécby chronické hepatitidy C hmotností a pohlavím pacienta a výsí vstupní viremie.

UNLABELLED: Today, the standard therapy of patients with chronic HCV (hepatitis C virus) infection is based on combination of pegylated interferon alpha (PEG-IFN) and ribavirin. THE STUDY OBJECTIVE: The aim of the study is to find correlations between patient's body weight, gender and baseline viral load and the efficacy of antiviral therapy in terms of achieving end-of-treatment viral response (ETVR) and sustained viral response (SVR). METHODS AND PATIENT SAMPLE: We enrolled 133 patients with chronic HCV infection. All of them were treated by combination of PEG-IFN alpha-2a (180 microg once a week) and ribavirin. Ribavirin doses were the following: For body weight < or = 74 kg - 800 mg daily in patients infected by genotype 2 (G2 - 3 patients) or G3 (18 patients), 1000 mg in patients infected by G1 (106 patients), G4 (1 patient) or G6 (1 patient); for body weight > or = 75 kg - 1200 mg daily in case of infection by G1. RESULTS: To date, 122 patients completed the therapy; 107 of them completed their therapy at least 24 weeks ago, so they can be assessed for SVR. ETVR was achieved in 76% and SVR in 60% patients. Statistically higher proportion of SVR was observed in women (p = 0.039), patients with relatively lower body weight (p = 0.034), patients in lower baseline viral load (p = 0.010) and patients with genotypes 2 and 3 (p = 0,008). Correlation analysis of individual predictive factors showed the statistically significant correlation between body weight and gender (p < 0.001), gender and baseline viral load (p = 0.027) and body weight and virus genotype (p = 0.003). Therefore, the only independent predictive factor of ETVR (p = 0.020) and SVR (p = 0.010) was the level of baseline viral load. CONCLUSION: Efficacy of PEG-IFN therapy is significantly influenced by the level of baseline viral load. According to the results of this study, patient's body weight and gender are not independent predictive factors that affect the therapy efficacy.

[The meaning of viral kinetics in the beginning of the pegylated interferon-alpha and ribavirin therapy for chronic hepatitis C]. / Význam virové kinetiky v pocátcích lécby chronické hepatitidy C pegylovaným interferonem alpha a ribavirinem.

UNLABELLED: Pegylated interferon alpha (PEG-IFN) and ribavirin combination therapy is the contemporary standard therapy of the patients chronically infected with hepatitis C virus (HCV). OBJECTIVE OF THE STUDY: The study is monitoring the changes in viremy through the changes of HCV RNA in serum before and during antiviral therapy and it attempts to find a relationship between the viral kinetics in the beginning of the therapy and the sustained virologic response. SET OF THE PATIENTS AND THE METHODICS: The study involved 133 patients with chronic infection with HCV, of the average age of 38 years (ranged 18-68 years). 86 of them were men. There were 88 patients who had not been treated before (naive patients), 19 of them were relabing and 26 were non-responders to the previous therapy with conventional IFNalpha and ribavirin. 106 patients (80%) were infected with genotype (G) 1, 3 (2%) with G2, 18 (14%) with G3, 1 patient with G4 and 1 with G6 (under 1%), in 4 (3%) the genotype could not be determined. All of them were treated with the combination of PEG-IFNalpha-2a (180 microg once a week) and ribavirin (800 mg per day in the infection with G2 or G3, 1000 mg at the infection with G1 and the weight up to 74 kg, 1200 mg per day at the infection with G1 and the weight 75 kg and higher). RESULTS: Up to now, 122 patients completed the therapy and 93 of them (76%) had negative HCV RNA in serum at the time of completion of the therapy. Negative HCV RNA after 24 weeks (sustained virologic response SVR) after the completion of the therapy had 64/107 (60%) of the treated patients. In the course of 12 weeks of the therapy the viremy decreased by at least 2 decadic logarithms (early virologic response - EVR) in 87 patients (82%) and in 63 of them (72%) also SVR was noted. Only 19 patients had not EVR and just 1 one of them, nevertheless, achieved SVR (5%). CONCLUSION: The achievement of EVR is a prerequisite to the successful therapy for chronic infection with HCV with the combination of PEG-IFNalpha and ribavirin. Quantitative determination of HCV RNA in serum before and during antiviral therapy is a prerequisite to the modern antiviral therapy for chronic infection with HCV.

Autoantibodies to asialoglycoprotein receptor in chronic hepatitis C patients.

The aim of this study was to determine the incidence of autoantibodies to asialoglycoprotein receptor (ASGPR, anti-ASGPR) in chronic hepatitis C patients and to characterize the anti-ASGPR-positive and anti-ASGPR-negative patients in more detail. A total of 79 chronic hepatitis C patients were screened for the presence anti-ASGPR by ELISA. Anti-ASGPR were detected in 11 (13.9%) patients. No significant differences were found between the anti-ASGPR-positive and anti-ASGPR-negative patients in age, alanine transaminase (ALT) activity, histological findings and response and tolerance to alpha-interferon (alpha-IFN) therapy. The male predominance in the anti-ASGPR positive group was statistically significant. It was surprising that other tested autoantibodies (antinuclear autoantibodies [ANA], smooth muscle autoantibodies [SMA], type 1 liver-kidney microsome autoantibodies [LKM-1], anti-thyroglobulin and thyroid microsome autoantibodies) and increased levels of immunoglobulins A, G and/or M were observed significantly more frequently in the anti-ASGPR-negative group.

Mechanism underlying bupivacaine inhibition of G protein-gated inwardly rectifying K+ channels.

Local anesthetics, commonly used for treating cardiac arrhythmias, pain, and seizures, are best known for their inhibitory effects on voltage-gated Na(+) channels. Cardiovascular and central nervous system toxicity are unwanted side-effects from local anesthetics that cannot be attributed to the inhibition of only Na(+) channels. Here, we report that extracellular application of the membrane-permeant local anesthetic bupivacaine selectively inhibited G protein-gated inwardly rectifying K(+) channels (GIRK:Kir3) but not other families of inwardly rectifying K(+) channels (ROMK:Kir1 and IRK:Kir2). Bupivacaine inhibited GIRK channels within seconds of application, regardless of whether channels were activated through the muscarinic receptor or directly via coexpressed G protein G(beta)gamma subunits. Bupivacaine also inhibited alcohol-induced GIRK currents in the absence of functional pertussis toxin-sensitive G proteins. The mutated GIRK1 and GIRK2 (GIRK1/2) channels containing the high-affinity phosphatidylinositol 4,5-bisphosphate (PIP(2)) domain from IRK1, on the other hand, showed dramatically less inhibition with bupivacaine. Surprisingly, GIRK1/2 channels with high affinity for PIP(2) were inhibited by ethanol, like IRK1 channels. We propose that membrane-permeant local anesthetics inhibit GIRK channels by antagonizing the interaction of PIP(2) with the channel, which is essential for G(beta)gamma and ethanol activation of GIRK channels.

Ion selectivity filter regulates local anesthetic inhibition of G-protein-gated inwardly rectifying K+ channels.

The weaver mutation (G156S) in G-protein-gated inwardly rectifying K+ (GIRK) channels alters ion selectivity and reveals sensitivity to inhibition by a charged local anesthetic, QX-314, applied extracellularly. In this paper, disrupting the ion selectivity in another GIRK channel, chimera I1G1(M), generates a GIRK channel that is also inhibited by extracellular local anesthetics. I1G1(M) is a chimera of IRK1 (G-protein-insensitive) and GIRK1 and contains the hydrophobic domains (M1-pore-loop-M2) of GIRK1 (G1(M)) with the N- and C-terminal domains of IRK1 (I1). The local anesthetic binding site in I1G1(M) is indistinguishable from that in GIRK2(wv) channels. Whereas chimera I1G1(M) loses K+ selectivity, although there are no mutations in the pore-loop complex, chimera I1G2(M), which contains the hydrophobic domain from GIRK2, exhibits normal K+ selectivity. Mutation of two amino acids that are unique in the pore-loop complex of GIRK1 (F137S and A143T) restores K+ selectivity and eliminates the inhibition by extracellular local anesthetics, suggesting that the pore-loop complex prevents QX-314 from reaching the intrapore site. Alanine mutations in the extracellular half of the M2 transmembrane domain alter QX-314 inhibition, indicating the M2 forms part of the intrapore binding site. Finally, the inhibition of G-protein-activated currents by intracellular QX-314 appears to be different from that observed in nonselective GIRK channels. The results suggest that inward rectifiers contain an intrapore-binding site for local anesthetic that is normally inaccessible from extracellular charged local anesthetics.

Efficacy of alpha-interferon therapy of chronic hepatitis patients infected with wild type hepatitis B virus and HBEAG-minus mutant.

The aim of this study was to evaluate the efficacy of alpha-interferon (alpha-IFN) treatment of 56 chronic hepatitis B (HB) patients positive for HB e antigen (HBeAg), which were previously not treated with alpha-IFN (group A). Seven of them, which did not respond to initial alpha-IFN treatment, were subjected to additional treatment with alpha-IFN (group B). Another 7 patients with chronic HB caused apparently by an HBeAg-minus HB virus (HBV) mutant represented group C. In the alpha-IFN treatment, 5 megaunits (MU) of alpha-IFN were administered subcutaneously three times a week for six months. A trend of improvement of important markers of the disease in the treated patients could be seen with increasing time after completion of the treatment even though it was not statistically significant. In group A, the absence of serum HBV DNA was found in 43% of the patients at the end of the treatment, in 41% 6 months later, and in 46% 12 months later. At the same time intervals group A showed negative HBeAg in 36%, 39% and 46%, positive anti-HBeAg in 36%, 38%, and 46%, negative HBsAg in 9%, 11%, and 14%, and normal level of alanine transaminase (ALT) in 23%, 39%, and 44%, respectively. A trend toward better results of alpha-interferon therapy for the group A patients displaying lower baseline viremia and higher ALT activity could be seen; however, this relationship was not statistically significant. Groups B and C were too small for statistical analysis. Nevertheless, 4 of 7 patients of group B were negative for HBV DNA 12 months after the treatment and HBV DNA was eliminated during the treatment in all patients of group C; however, 3 patients relapsed after the treatment.

Defective gamma-aminobutyric acid type B receptor-activated inwardly rectifying K+ currents in cerebellar granule cells isolated from weaver and Girk2 null mutant mice.

Stimulation of inhibitory neurotransmitter receptors, such as gamma-aminobutyric acid type B (GABAB) receptors, activates G protein-gated inwardly rectifying K+ channels (GIRK) which, in turn, influence membrane excitability. Seizure activity has been reported in a Girk2 null mutant mouse lacking GIRK2 channels but showing normal cerebellar development as well as in the weaver mouse, which has mutated GIRK2 channels and shows abnormal development. To understand how the function of GIRK2 channels differs in these two mutant mice, we compared the G protein-activated inwardly rectifying K+ currents in cerebellar granule cells isolated from Girk2 null mutant and weaver mutant mice with those from wild-type mice. Activation of GABAB receptors in wild-type granule cells induced an inwardly rectifying K+ current, which was sensitive to pertussis toxin and inhibited by external Ba2+ ions. The amplitude of the GABAB receptor-activated current was severely attenuated in granule cells isolated from both weaver and Girk2 null mutant mice. By contrast, the G protein-gated inwardly rectifying current and possibly the agonist-independent basal current appeared to be less selective for K+ ions in weaver but not Girk2 null mutant granule cells. Our results support the hypothesis that a nonselective current leads to the weaver phenotype. The loss of GABAB receptor-activated GIRK current appears coincident with the absence of GIRK2 channel protein and the reduction of GIRK1 channel protein in the Girk2 null mutant mouse, suggesting that GABAB receptors couple to heteromultimers composed of GIRK1 and GIRK2 channel subunits.

Reopening of single L-type Ca2+ channels in mouse cerebellar granule cells: dependence on voltage and ion concentration.

1. We recorded the activity of single L-type Ca2+ channels from cell-attached patches on mouse cerebellar granule cells. The experiments investigated the mechanism of channel reopening at negative membrane potentials following a strong depolarization. 2. L-type channels that reopened following a strong depolarization showed a wide distribution of single-channel conductances, which ranged from 16 to 28 pS in the presence of 90 mM Ba2+. 3. The distribution of the latencies before reopening was fitted as the sum of two exponential components with time constants tau f approximately 1 and tau s approximately 12 ms at -70 mV. Hyperpolarization reduced the time constant of the slower component approximately e-fold per 43 mV, but had no effect on the faster component. 4. Raising the concentration of external Ba2+ reduced the time constant of the slower component of the reopening latency without altering the fast component. The time constant of the slow component was approximately 27 ms in 10 mM Ba2+ and decreased to 12 ms in 90 mM Ba2+ at -70 mV. The relation between the time constant and external Ba2+ saturated with an apparent KD of approximately 20 mM. 5. The distribution of reopening times was best fitted as the sum of two exponential components with time constants tau f approximately 0.5 ms and tau s approximately 4.5 ms at -70 mV. The conditional latencies before reopening into either the short or long open state were indistinguishable. 6. The results are consistent with the idea that a positively charged blocker occludes the pore during depolarization and channels reopen as the blocker dissociates following repolarization to negative potentials.

Functional effects of the mouse weaver mutation on G protein-gated inwardly rectifying K+ channels.

The weaver mutation corresponds to a substitution of glycine to serine in the H5 region of a G protein-gated inwardly rectifying K+ channel gene (GIRK2). By studying mutant GIRK2 weaver homomultimeric channels and heteromultimeric channels comprised of GIRK2 weaver and GIRK1 in Xenopus oocytes, we found that GIRK2 weaver homomultimeric channels lose their selectivity for K+ ions, giving rise to inappropriate receptor-activated and basally active Na+ currents, whereas heteromultimers of GIRK2 weaver and GIRK1 appeared to have reduced current. Immunohistochemical localization indicates that GIRK2 and GIRK1 proteins are expressed in the cerebellar neurons of mice at postnatal day 4, at a time when these neurons normally undergo differentiation. Thus, the aberrant behavior of mutant GIRK2 weaver channels could affect the development of weaver mice in at least two distinct ways.

Evidence that direct binding of G beta gamma to the GIRK1 G protein-gated inwardly rectifying K+ channel is important for channel activation.

Activation of G protein-gated K+ channels by G protein-coupled receptors contributes to parasympathetic regulation of heart rate in the atrium and inhibitory postsynaptic potentials in the peripheral and central nervous system. Having found that G beta gamma activates the cloned GIRK1 channel, we now report evidence for direct binding of G beta gamma to both the N-terminal hydrophilic domain and amino acids 273-462 of the C-terminal domain of GIRK1. These direct interactions are physiologically important because synthetic peptides derived from either domain reduce the G beta gamma binding as well as the G beta gamma activation of the channel. Moreover, the N-terminal domain may also bind trimeric G alpha beta gamma, raising the possibility that physical association of G protein-coupled receptors, G proteins, and K+ channels partially accounts for their compartmentalization and hence rapid and specific channel activation by receptors.

Identification of structural elements involved in G protein gating of the GIRK1 potassium channel.

Chimeras of GIRK1 and IRK1, a G protein-insensitive inward rectifier, are activated by coexpression of G beta gamma if they contain either the N-terminal or part of the C-terminal hydrophilic domain of GIRK1. The N-terminal domain of GIRK1 also facilitates the fast rates of activation and deactivation following m2 muscarinic receptor stimulation. The hydrophobic core of GIRK1 (M1-H5-M2) is important for determining the brief single-channel open times typical of GIRK1 but not important for determining G beta gamma sensitivity. Coexpression with CIR revealed that the gating properties associated with different GIRK1 domains could not have arisen from altered ability to form heteromultimers. These results implicate specific regions of GIRK1 in G protein activation and suggest that GIRK1 may be closely linked to the m2 muscarinic receptor-G protein complex.

Activation of the cloned muscarinic potassium channel by G protein beta gamma subunits.

Acetylcholine released during parasympathetic stimulation of the vagal nerve slows the heart rate through the activation of muscarinic receptors and subsequent opening of an inwardly rectifying potassium channel. The activation of these muscarinic potassium channels is mediated by a pertussis toxin-sensitive heterotrimeric GTP-binding protein (G protein). It has not been resolved whether exogenously applied G alpha or G beta gamma, or both, activate the channel. Using a heterologous expression system, we have tested the ability of different G protein subunits to activate the cloned muscarinic potassium channel, GIRK1. We report here that coexpression of GIRK1 with G beta gamma but not G alpha beta gamma in Xenopus oocytes results in channel activity that persists in the absence of cytoplasmic GTP. This activity is reduced by fusion proteins of the beta-adrenergic receptor kinase and of recombinant G alpha i-GDP, both of which are known to interact with G beta gamma. Moreover, application of recombinant G beta gamma, but not G alpha i-GTP-gamma S, activates GIRK1 channels. Thus G beta gamma appears to be sufficient for the activation of GIRK1 muscarinic potassium channels.

The S4-S5 loop contributes to the ion-selective pore of potassium channels.

Mutagenesis experiments on voltage-gated K+ channels have suggested that the ion-selective pore is comprised mostly of H5 segments. To see whether regions outside of the H5 segment might also contribute to the pore structure, we have studied the effect of single amino acid substitutions in the segment that connects the S4 and S5 putative transmembrane segments (S4-S5 loop) on various permeation properties of Shaker K+ channels. Mutations in the S4-S5 loop alter the Rb+ selectivity, the single-channel K+ and Rb+ conductances, and the sensitivity to open channel block produced by intracellular tetraethylammonium ion, Ba2+, and Mg2+. The block of Shaker K+ channels by intracellular Mg2+ is surprising, but is reminiscent of the internal Mg2+ blockade of inward rectifier K+ channels. The results suggest that the S4-S5 loop constitutes part of the ion-selective pore. Thus, the S4-S5 loop and the H5 segment are likely to contribute to the long pore characteristic of voltage-gated K+ channels.

Primary structure and functional expression of a rat G-protein-coupled muscarinic potassium channel.

Parasympathetic nerve stimulation causes slowing of the heart rate by activation of muscarinic receptors and the subsequent opening of muscarinic K+ channels in the sinoatrial node and atrium. This inwardly rectifying K+ channel is coupled directly with G protein. Based on sequence homology with cloned inwardly rectifying K+ channels, ROMK1 (ref. 11) and IRK1 (ref. 12), we have isolated a complementary DNA for a G-protein-coupled inwardly rectifying K+ channel (GIRK1) from rat heart. The GIRK1 channel probably corresponds to the muscarinic K+ channel because (1) its functional properties resemble those of the atrial muscarinic K+ channel and (2) its messenger RNA is much more abundant in the atrium than in the ventricle. In addition, GIRK1 mRNA is expressed not only in the heart but also in the brain.

Dihydropyridine- and omega-conotoxin-sensitive Ca2+ currents in cerebellar neurons: persistent block of L-type channels by a pertussis toxin-sensitive G-protein.

The inhibition of high-threshold Ca2+ channel currents by activated G-proteins was studied in mouse cerebellar granule cells making use of the hydrolysis-resistant GTP analog GTP-gamma-S. When individual granule cells were internally dialyzed with GTP-gamma-S, the high-threshold Ca2+ current decreased to approximately 20% of its initial value within approximately 2 min. The GTP-gamma-S-resistant current was reduced further by the subsequent addition of either omega-conotoxin or dihydropyridine antagonist, indicating that both N- and L-type Ca2+ channels carried the remaining current. Continuous exposure to the dihydropyridine agonist +(S)-202-791 caused a rapid increase in the GTP-gamma-S-resistant current. The L-type current evoked by the agonist subsequently decreased to the level observed prior to adding the drug following a time course similar to the initial inhibition of the total high-threshold current. A second application of the drug at a later time failed to increase the current a second time, indicating a persistent blockade of the agonist-evoked L-current. Pretreating cells with pertussis toxin prevented the initial inhibition of the total whole-cell Ca2+ channel current as well as the subsequent inhibition of the agonist-evoked L-current. The results show that a pertussis toxin-sensitive G-protein produces a persistent inhibition of L-type Ca2+ channels in these central neurons.

[IgA antibodies against Epstein-Barr virus capsid antigen]. / Protilátky trídy iga proti kapsidovému antigenu viru Epsteina-Barrové.

The authors describe infection with the Epstein-Barr virus (EBV) which is associated with the formation of various types of antibodies--heterophil (HP) antibodies as well as antibodies against individual EBV antigens. They evaluate the contribution of a recently elaborated and introduced method used for detection of antibodies against the capsid antigen of the EBV class IgA (anti-VCA IgA) by indirect immunofluorescence to the diagnosis of acute and chronic EBV infections. Anti-VCA IgA are useful in the diagnosis of EBV infections if the patient has no longer HP and anti-VCA IgM, but only anti-VCA IgG. If, however, in addition to anti-VCA IgA also anti-VCA IgA are present, their presence can be the only detectable sign of a recent EBV infection and also a sign of reactivation of chronic EBV infection.

Reopening of Ca2+ channels in mouse cerebellar neurons at resting membrane potentials during recovery from inactivation.

Recordings of single-channel activity from cerebellar granule cells show that a component of Ca2+ entry flows through L-type Ca2+ channels that are closed at negative membrane potentials following a strong depolarization, but then open after a delay. The delayed openings can be explained if membrane depolarization drives Ca2+ channels into an inactivated state and some channels return to rest through the open state after repolarization. Whole-cell recordings show that the charge carried by Ca2+ during the tail increases as inactivation progresses, whereas the current during the voltage step decreases. Voltage-dependent inactivation may be a general mechanism in central neurons for enhancing Ca2+ entry by delaying it until after repolarization, when the driving force for ion entry is large. Modifying the rate and extent of inactivation would have large effects on Ca2+ entry through those channels that recover from inactivation by passing through the open state.

Inactivating and non-inactivating dihydropyridine-sensitive Ca2+ channels in mouse cerebellar granule cells.

1. Granule cells were dissociated from mouse cerebellum and grown in vitro. Currents through single Ca2+ channels were recorded from the cell body with the patch clamp technique. 2. Voltage steps to 0 mV produced brief channel openings with a mean open time of approximately 0.5 ms. The single-channel conductance measured from the amplitude of the single-channel current with 90 mM-Ba2+ in the patch electrode was 22 pS. 3. The probability of Ca2+ channel opening increased with test potentials more positive than -30 mV, with half-activation near 0 mV, and followed the Boltzmann relation for the activation of whole-cell Ca2+ current. 4. Voltage steps to potentials more positive than 0 mV produced more channel activity at the beginning than at the end of the voltage step. The average of the single-channel currents decayed to a non-zero level with a time course similar to that of the whole-cell Ca2+ current. 5. The amplitude as well as the decay of the mean current measured during a test pulse to 0 mV was reduced as the holding potential was made more positive than approximately -90 mV. The change in the open channel probability with holding potential followed the Boltzmann relation which described the inactivation of the whole-cell Ca2+ current. 6. Ca2+ channel activity persisted for over several minutes after excising the patch from the cell body when intracellular cyclic AMP was increased. After patch excision, the number of functional channels decreased to a level where only one channel at a time was active. Ca2+ channel openings appeared as either short bursts at the beginning of the voltage step or long bursts that lasted throughout the pulse. 7. Exposing the cell to the dihydropyridine agonist +(S)-202-791 markedly increased the fraction of sweeps with long openings and produced a non-decaying mean current that was approximately 5 times larger than control. In a fraction of the sweeps, however, long openings occurred more frequently at the beginning than at the end of the voltage step and these produced a decaying mean current. 8. Shifting the holding potential to more positive potentials in the presence of the dihydropyridine agonist preferentially reduced the number of brief openings while sparing the long openings. The amplitude of the mean current was similar to that obtained from the more negative holding potential and there was no change in the fraction of sweeps with long openings that occurred at the beginning of the voltage pulse.(ABSTRACT TRUNCATED AT 400 WORDS)

Inactivation of calcium currents in granule cells cultured from mouse cerebellum.

1. Cells dissociated from mouse cerebellum were grown in vitro. Ca2+ channel currents were recorded from granule cells with the patch-clamp technique under conditions which suppressed currents through Na+ and K+ channels and minimized run-down of current through Ca2+ channels. 2. A strong depolarizing voltage step from a hyperpolarized holding potential produced inward Ca2+ channel current that decayed exponentially to a non-zero level. Inward current decayed to approximately 40% of its peak amplitude (range 20-90%). 3. The inward current increased in amplitude when Ca2+ was replaced with Ba2+ or after raising the concentration of extracellular Ba2+, but the rate of decay of current was unaffected. 4. The current-voltage (I-V) relation showed that peak or sustained current increased with voltage pulses more positive than approximately -30 mV, reached a maximum amplitude near +20 mV and became progressively smaller with larger depolarizations. 5. The tail currents produced after rapidly repolarizing the membrane potential to -70 mV from a positive test pulse decayed along a single exponential time course with a time constant of approximately 0.5 ms. The amplitude of tail current measured at a fixed repolarization potential increased as the pre-pulse was made more positive and reached a maximum with pre-pulses more positive than +40 mV. A plot of normalized amplitude of the tail current as a function of the pre-pulse potential was fitted with a Boltzmann relation with V1/2 = approximately + 8 mV and steepness k = 14 mV. 6. Shifting the holding potential to more positive potentials reduced the amplitude of the Ca2+ channel current elicited by the fixed voltage step and abolished the decay of the inward current. The peak current was normalized to the maximum peak current elicited from a very negative holding potential and plotted as a function of holding potential. The points were fitted with a Boltzmann relation for inactivation with V1/2 = approximately -57 mV and steepness k = 14 mV. 7. The onset of inactivation was studied in two-pulse experiments in which the duration of conditioning pre-pulse was varied. Increasing the duration of a pre-pulse to a fixed potential reduced the peak inward current evoked by the second test pulse. Plotting normalized current as a function of pre-pulse duration showed that inactivation developed along a double exponential time course. Both fast and slow time constants decreased as the pre-pulse potential was made more positive.(ABSTRACT TRUNCATED AT 400 WORDS)