Talking about bioelectrical potentials using rings of the mesenteric artery without glass micropipettes

Abstract

In the present study, a practical activity is proposed to adopt an experimental approach to demonstrate the relationship between the equilibrium potential for K(+) and transmembrane electrical potential without glass micropipettes. A conventional setup for recording contractile activity of isolated smooth muscle preparations was used based on the events elegantly described by Somlyo and Somlyo in the 1960s. They showed that, in response to a given stimulus, smooth muscle cells may contract, recruiting electromechanical or pharmacomechanical coupling by mechanisms that involve, or not, changes in transmembrane potential, respectively. By means of contractions and relaxations of a ring-like preparation from the rat mesenteric artery, it is possible to observe the functional consequences of handling K(+) concentration in the extracellular compartment and the effects caused by opening K(+) channels in that preparation, which are significant when the cell membrane establishes an electrical potential difference between intra- and extracellular compartments (driven mainly by K(+) permeability under resting conditions). The effects observed by students fit well with values predicted by Nernst and Goldman-Hodgin-Katz equations, and we demonstrated that the activity is able to improve students' comprehension regarding basic principles of bioelectricity.

An intuitive approach to understanding the resting membrane potential

“…Thurman (20) developed a preparation using frog Sartorius muscle for demonstrating the role of K ϩ in setting V m and also used the exercise to teach students hypothesis testing. Ribiero-Filho et al (16) used the contractions in a ring-like preparation from rat mesenteric artery as an indicator of changes in membrane potential in response to changes in ionic gradients. Schwab et al (17) developed a demonstration of V m by measuring the membrane potential of Xeonopus laevis oocytes in response to stepwise changes in external K ϩ .…”

The triterpenoid alpha, beta-amyrin prevents the impaired aortic vascular reactivity in high-fat diet-induced obese mice

“…Targeted PKG then modulates additional phenomena such as the gating of K + channels, which results in membrane hyperpolarization and smooth muscle relaxation (Kubo et al 1994). In the present study, the vasorelaxant effects of SNP under a KCl stimulus were significantly reduced compared to the PHE-induced contractions, likely because the relaxant efficacy of compounds that recruit hyperpolarizing phenomena involving the opening of K + channels, such as SNP, is lost under depolarizing conditions imposed by a high extracellular (60 mM) K + concentration (Ribeiro-Filho et al 2012). In addition, the relaxing effects of SNP did not differ between tissues obtained from mice subjected to different diet regimens.…”

Vasorelaxant effects of 2‐nitro‐1‐phenyl‐1‐propanol in rat aorta

“…Removal of the endothelial layer diminished its EC 50 to relax phenylephrine, which may suggest a direct effect of NPP on smooth muscle cells without the induction of nitric oxide release by the endothelium. Hyperpolarization that resulted from the opening of K + channels is also unlikely one of the mechanisms of action of NPP in rat aorta because its relaxant effects occurred with a similar profile at both 60 and 120 mmol/L K + .K + channel openers per se cannot relax depolarized smooth muscle cells 20. Additionally, the pharmacological blockade of K + channels with tetraethylammonium, glibenclamide, and 4-aminopyridine did not change the relaxant actions of NPP.…”