RESUMO
The regulation by Ca2+ of Ca2+-permeable ion channels represents an important mechanism in the control of cell function. Polycystin-2 (PC2, TRPP2), a member of the TRP channel family (Transient Potential Receptor), is a Ca2+ permeable non-selective cation channel. Previous studies from our laboratory demonstrated that physiological concentrations of Ca2+ do not regulate in vitro translated PC2 (PC2iv) channel activity. However, the issue as to PC2's Ca2+ permeability and regulation remain ill-defined, in particular because Ca2+ transport is usually observed in the presence of other ionic gradients. In this study, we assessed Ca2+ transport by PC2iv in a lipid bilayer reconstitution system in a high Ca2+ gradient (CaCl2 100 mM cis, CaCl2 10 mM trans) in the presence of either 3:7 or 7:3 1-palmitoyl-2-oleoyl-choline and ethanolamine lipid mixtures. Reconstituted PC2iv showed spontaneous Ca2+ currents in both lipid mixtures, with a maximum conductance of 63 ± 13 pS (n = 19) and 105 pS ± 9.8 (n = 9), respectively. In both cases, we best fitted the experimental data with the Goldman-Hodgkin-Katz equation, observing a reversal potential (Vrev â¼ -27 mV) consistent with strict Ca2+ selectivity. The R742X mutated PC2 (PC2R742X), lacking the carboxy terminal domain of the channel showed no differences with wild type PC2. Interestingly, we also observed the onset of spontaneous Ca2+ current oscillations whenever PC2-containing samples were reconstituted in the 3:7, but not 7:3 POPC:POPE lipid mixture. The amplitude and frequency of the ionic oscillations were highly dependent on the applied voltage, the imposed Ca2+ gradient, and the presence of high Ca2+, which induced PC2 channel clustering as observed by atomic force microscopy (AFM). We also used the QuB suite to kinetically model the PC2 channel Ca2+ oscillations based on the presence of subconductance states in the channel. The encompassed evidence supports a high Ca2+ permeability by PC2, and a novel oscillatory mechanism dependent on the presence of Ca2+ and phospholipids that provides the first evidence for the relation between stochasticity and deterministic processes mediated by ion channels.
Assuntos
Cálcio , Canais de Cátion TRPP , Canais de Cátion TRPP/genética , Canais de Cátion TRPP/metabolismo , Cálcio/metabolismo , Cloreto de Cálcio/metabolismo , Bicamadas Lipídicas , Transporte de ÍonsRESUMO
As in other Latin American populations, Argentinians are the result of the admixture amongst different continental groups, mainly from America and Europe, and to a lesser extent from Sub-Saharan Africa. However, it is known that the admixture processes did not occur homogeneously throughout the country. Therefore, considering the importance for anthropological, medical and forensic researches, this study aimed to investigate the population genetic structure of the Argentinian Patagonia, through the analysis of 46 ancestry informative markers, in 433 individuals from five different localities. Overall, in the Patagonian sample, the average individual ancestry was estimated as 35.8% Native American (95% CI: 32.2-39.4%), 62.1% European (58.5-65.7%) and 2.1% African (1.7-2.4%). Comparing the five localities studied, statistically significant differences were observed for the Native American and European contributions, but not for the African ancestry. The admixture results combined with the genealogical information revealed intra-regional variations that are consistent with the different geographic origin of the participants and their ancestors. As expected, a high European ancestry was observed for donors with four grandparents born in Europe (96.8%) or in the Central region of Argentina (85%). In contrast, the Native American ancestry increased when the four grandparents were born in the North (71%) or in the South (61.9%) regions of the country, or even in Chile (60.5%). In summary, our results showed that differences on continental ancestry contribution have different origins in each region in Patagonia, and even in each locality, highlighting the importance of knowing the origin of the participants and their ancestors for the correct interpretation and contextualization of the genetic information.