CONICET | Buscador de Institutos y Recursos Humanos

Our aim was to study the diversity of ionic channels activated by voltage stimuliin isolated human umbilical artery (HUA) smooth muscle cells. We used the patchclamptechnique in the cell-attached (CA) and the inside-out (IO) configurations.The experiments were performed in symmetric K+ conditions recording thestationary activity of channels in CA configuration and after that, the patch was excisedand new recordings were performed in IO configuration (K+ symmetric condition and avery low Ca2+ concentration facing with the intracellular side of the membrane patch).In such recording conditions, selective K+ channels and non selective cationic channelswould be recorded, both of which have important physiological roles in vascular smoothmuscle. K+ channels are important for the maintenance and regulation of cell membranepotential, its activation producing hyperpolarization and less cell excitability, while theactivation of non selective cationic channels induce depolarization and increase cellexcitability.More that one type of channel appeared in each membrane patch. In the CAconfiguration (52 cells) the frequency of apparition of the different conductance valueswas: 29 % of the cells showed high conductance channels (range: 200-300 pS); 61% and50 % showed intermediate conductances included in the range of 100-200 pS and 50-100 pS, respectively; and finally, 27 % of the cells showed channels in the lowconductance range (50-30 pS). In all cases, the frequency of apparition of ionic channelsdiminished in the IO configuration, where the values for the same ranges ofconductances were: 15 % for high conductances, 30 % and 32% for intermediateconductances and 17% for low conductances. It is important to note that, in contrast tothe CA configuration where the cell is intact, in IO the membrane patch is detachedfrom the cell and so, the ionic channels whose activity depend on intracellular factorsmay have disappeared or diminished. Alternatively, some channels may have beeninhibited by intracellular factors in CA configuration and once detached form the cellcould become active. Some of these properties were further studied: for example, inHUA smooth muscle cells, an increase in Ca2+ concentration in the solution facing theintracellular side of cell membrane increased the activity of some K+ ionic channels,such as the high-conductance voltage and Ca2+ activated K+ channel, which is highlyexpressed in smooth muscle cells. A decrease in the pH (from 7.4 to 6.8) of the solutionin contact with the intracellular side of cell membrane activated high and intermediateionic conductances. We also tested on IO patches the effects of intracellular secondmessengers like arachidonic acid, observing that this substance is able to activate highand intermediate ionic conductances. So far, we have presented a description of ionicchannels present in these native smooth muscle cells and the effect of some of theirphysiological regulators. Further research is necessary to increase the knowledge of theelectrophysiological properties of the complete diversity of ionic channels and theirpossible mechanisms of regulation.