Heterotypic docking of Cx43 and Cx45 connexons blocks fast voltage gating of Cx43.

Immunohistochemical co-localization of distinct connexins (Cxs) in junctional areas suggests the formation of heteromultimeric channels. To determine the docking effects of the heterotypic combination of Cx43 and Cx45 on the voltage-gating properties of their channels, we transfected DNA encoding Cx43 or Cx45 into N2A neuroblastoma or HeLa cells. Using a double whole-cell voltage-clamp technique, we determined macroscopic and single-channel gating properties of the intercellular channels formed. Cx43-Cx45 heterotypic channels had rectifying properties where Cx45 connexons inactivated rapidly upon hyperpolarizing voltage pulses applied to the Cx45-expressing cell. During depolarizing pulses to the Cx45-expressing cell, Cx43 connexons inactivated with substantially reduced kinetics as compared with homotypic Cx43 channels. Similar slow kinetics was observed for homotypic Cx43M257 (truncation mutant). Heterotypic channels had a main conductance whose value was predicted by the sum of corresponding homomeric connexon conductances; it was not voltage dependent and had no detectable residual conductance. The voltage-gating kinetics of heterotypic channels and their single-channel behavior implicate a role for the Cx43 carboxyl-terminal domain in the fast gating mechanism and in the establishment of residual conductance. Our results also suggest that heterotypic docking may lead to conformational changes that inhibit this action of the Cx43 carboxyl-terminal domain.

Junctional communication between isolated pairs of canine atrial cells is mediated by homogeneous and heterogeneous gap junction channels.

INTRODUCTION: The expression of multiple connexins (Cxs) in the canine right atria raises the possibility that heterogeneous gap junction channels might be formed. METHODS AND RESULTS: We compared the unitary conductance (gamma(j)) of gap junction channels between isolated canine atrial cell pairs with those of homogeneous cardiac gap junction channels expressed in other systems. After partial uncoupling with halothane (2 mmol/L), the (gamma)j calculations for atrial isolated cardiocytes ranged from 30 to 220 pS and their distribution in event histograms was spread over the entire range, with a small peak at approximately 100 pS. This distribution deviates from the discrete peaks calculated from (gamma)j of homogeneous channels. All-points histograms of junctional current traces revealed distinct open-state levels. Some of these are related to the main open state of connexin43 (Cx43) (approximately 100 pS), observed between canine ventricular cells, or connexin40 (Cx40) (approximately 215 pS) observed between transfected N2A cells under similar recording conditions. Intermediate values for (gamma)j were not observed in recordings from ventricular cells, which express mostly Cx43, nor in those from N2A cells expressing Cx40, but were observed consistently between atrial cells. Because they were measured as first openings from the nonconductance state, these intermediate values most likely represent main conductance states of heterogeneous channels rather than subconductance states of homogeneous channels. CONCLUSION: This suggests that regulation of cell-to-cell coupling in the heart depends not only on posttranslational modulation of preexisting Cxs, but also on the intracellular assembly mechanisms, and the way individual Cxs interact with others within a connexon and/or with other connexons from adjacent cells.

Ionotropic GABA receptor from lobster olfactory projection neurons.

This study reports an ionotropic GABA (gamma-aminobutyric acid) receptor in projection neurons acutely dissociated from the olfactory lobe of the brain of the spiny lobster and analyzed by whole cell and cell-free patch-clamp recording. GABA evokes a macroscopic current in the cells that is linear from -100 to + 100 mV, reverses at the imposed chloride equilibrium potential, has a permeability sequence of Cl- > acetate > bicarbonate > phosphate > propionate and SCN- > Br- > I- > Cl- > F-, and is reversibly blocked by the Cl channel blocker picrotoxin but not tert-butylbicyclophosphorothionate (TBPS). The current is bicuculline insensitive and activated by muscimol, isoguvacine, cis-4-aminocrotonic acid (CACA), and trans-aminocrotonic acid (TACA), as well as by the GABA(C)-receptor antagonists 4,5,6,7-tetrahydroisoxazolo [5,4,-c]pyridin-3-ol (THIP), 3-amino-1-propanesulfonic acid (3-APS), and imidazole-4-acetic acid (I-4AA), but not the GABA(B)-receptor agonists baclofen and 3-aminopropylphosphonic acid (3-APA). Agonist potency for the receptor is TACA > muscimol > GABA > I-4AA > isoguvacine > 3-APS > CACA > THIP. Unitary chloride currents in cell-free, outside-out patches from the cells share enough of these pharmacological properties to indicate that the channel underlies the macroscopic current. The receptor mediates an inhibitory current in the cells in vivo. The receptor is similar, if not identical, to one from neurons cultured from the thoracic ganglia of the clawed lobster. The more extensive pharmacological characterization of the receptor reported here indicates that this lobster CNS receptor is pharmacologically distinct from previously characterized ionotropic GABA receptors.

[The Oradea study regarding the epidemiology factors in ischemic cardiopathy]. / Studiul Oradea privind depistarea si epidemiologia factorilor de risc în cardiopatia ischemia. I) Hipercolesterolemia.

Cholesterolemia in a population of 100482 inhabitants of the Bihor district, subjected to screening for the risk factors in ischemic cardiopathy were studied. Together with hyperlipidemias other risk factors were detected: arterial hypertension, obesity, diabetes mellitus, smoking, ischemic alterations of the electrocardiogram, the influence of the noxious agents present at the working place, of the blood groups and disturbances of the menstrual cycle. The mean cholesteremia is of 205 ± 43.7 mgr% (M = 207 ± 43.7 mgr%; F = 204 ± 43.5 mgr%). The prevalence of cholesterolemia, in comparison with the higher normal limits in each age group over 15 years of age, is in the entire studied series, of 13.5%. The population in whom cholesterolemia exceeds 250 mgr% represents 13.92%.