Single-channel ionic conductances in smooth muscle cells from human umbilical artery

MARTIN P; ROLDAN PALOMO AR; ENRIQUE N; REBOLLEDO A; PICCININI L; VILCHE M; MILESI V

La Plata

Congreso; Humboldt Kolleg - International Conference on Physics; 2011

Our aim was to study the diversity of ionic channels activated by voltage stimuli in isolated human umbilical artery (HUA) smooth muscle cells. We used the patch-clamp technique in the cell-attached (CA) and the inside-out (IO) configurations.The experiments were performed in symmetric K+ conditions recording the stationary activity of channels in CA configuration and after that, the patch was excised and new recordings were performed in IO configuration (K+ symmetric condition and a very low Ca2+ concentration facing with the intracellular side of the membrane patch). In such recording conditions, selective K+ channels and non selective cationic channels would be recorded, both of which have important physiological roles in vascular smooth muscle. K+ channels are important for the maintenance and regulation of cell membrane potential, its activation producing hyperpolarization and less cell excitability, while the activation of non selective cationic channels induce depolarization and increase cell excitability. More that one type of channel appeared in each membrane patch. In the CA configuration (52 cells) the frequency of apparition of the different conductance values was: 29 % of the cells showed high conductance channels (range: 200-300 pS); 61% and 50 % 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 low conductance range (50-30 pS). In all cases, the frequency of apparition of ionic channels diminished in the IO configuration, where the values for the same ranges of conductances were: 15 % for high conductances, 30 % and 32% for intermediate conductances and 17% for low conductances. It is important to note that, in contrast to the CA configuration where the cell is intact, in IO the membrane patch is detached from the cell and so, the ionic channels whose activity depend on intracellular factors may have disappeared or diminished. Alternatively, some channels may have been inhibited by intracellular factors in CA configuration and once detached form the cell could become active. Some of these properties were further studied: for example, in HUA smooth muscle cells, an increase in Ca2+ concentration in the solution facing the intracellular 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 highly expressed in smooth muscle cells. A decrease in the pH (from 7.4 to 6.8) of the solution in contact with the intracellular side of cell membrane activated high and intermediate ionic conductances. We also tested on IO patches the effects of intracellular second messengers like arachidonic acid, observing that this substance is able to activate high and intermediate ionic conductances. So far, we have presented a description of ionic channels present in these native smooth muscle cells and the effect of some of their physiological regulators. Further research is necessary to increase the knowledge of the electrophysiological properties of the complete diversity of ionic channels and their possible mechanisms of regulation.