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

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.

Ontogeny of chicken ductus arteriosus response to oxygen and vasoconstrictors

The present study aimed to characterize the contractile reactivity of the chicken ductus arteriosus (DA) from the last stage of prenatal development and throughout the perinatal period. Isolated DA rings from 15-day, noninternally-pipped 19-day, and externally-pipped 21-day embryos were studied using myograph techniques. On embryonic day 15, the chicken DA did not respond to O2 (0 to 21%), norepinephrine (NE), or phenylephrine (Phe) but contracted in response to high-K+ solution, the inhibitor of voltage-gated channels 4-aminopyridine, U-46619, and endothelin (ET)-1. These responses increased with advancing incubation age. Contractile responses to O2, NE, and Phe were present in the 19- and 21-day embryo. Oxygen-induced contraction was restricted to the pulmonary side of the DA and was augmented by the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester and the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one and reduced by the peptidic ETA and ETB-receptor antagonist PD-142,893. Transmural electrical stimulation of nerves, the nonselective cyclooxygenase (COX) inhibitor indomethacin, the COX-1 inhibitor valeryl salicylate, the COX-2 inhibitor nimesulide, the inhibitor of ATP-sensitive K+ channels glibenclamide, and the inhibitor of Ca2+-activated K+ channels tetraethylammonium did not cause contraction of the DA rings at any age. We conclude that transition to ex ovo life is accompanied by dramatic changes in chicken DA reactivity. At 0.7 incubation, excitation-contraction and pharmacomechanical coupling for several contractile agonists are already present, whereas the constrictor effects of O2 and cathecolamines appear later in development and are located in the pulmonary side of the DA.

Fetal cerebrovascular acclimatization responses to high-altitude, long-term hypoxia: a model for prenatal programming of adult disease?

During the past several decades, many risk factors for cerebrovascular and cardiovascular disease have been identified. More recently, it has been appreciated that inadequate nutrition and/or other intrauterine factors during fetal development may play an important role in the genesis of these conditions. An additional stress factor that may “program” the fetus for disease later in life is chronic hypoxia. In studies originally designed to examine the function of developing cerebral arterial function in response to long-term hypoxia (LTH), it has become clear that many cellular and subcellular changes may have important implications for later life. Here we review some of the significant alterations in fetal cerebral artery structure and function induced by high-altitude (3,820 m, 12,470 ft) LTH (∼110 days). LTH is associated with augmentation or upregulation of presynaptic functions, including responses to perivascular (i.e., sympathetic) nerve stimulation, and structural maturational changes. In contrast, many postsynaptic functions related to the Ca2+-dependent contractile pathway tend to be downregulated, whereas elements of the Ca2+-independent contraction pathway are upregulated. The results emphasize the role of high-altitude LTH in modulating many aspects of electromechanical and pharmacomechanical coupling in the developing cerebral vasculature. A complicating factor is that the regulation of cerebrovascular tone by Ca2+-dependent and Ca2+-independent pathways changes significantly as a function of maturational age. In addition to highlighting independent regulation of various elements of the signal transduction cascade, the studies demonstrate the potential for LTH to program the fetus for cerebrovascular and other disease as an adult.

Effect of cortisol on norepinephrine-mediated contractions in ovine uterine arteries

Cortisol potentiated norepinephrine (NE)-mediated contractions in ovine uterine arteries (UA). We tested the hypothesis that cortisol regulated α1-adrenoceptor-mediated pharmacomechanical coupling differentially in nonpregnant UA (NUA) and pregnant UA (PUA). Cortisol (10 ng/ml for 24 h) significantly increased contractile coupling efficiency of α1-adrenoceptors in NUA, but increased α1-adrenoceptor density in PUA. Cortisol potentiated NE-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] synthesis in both NUA and PUA, but increased coupling efficiency of α1-adrenoceptors to Ins(1,4,5)P3synthesis only in NUA. Carbenoxolone alone did not affect NE-mediated Ins(1,4,5)P3 production, but significantly enhanced cortisol-mediated potentiation of NE-stimulated Ins(1,4,5)P3 synthesis in PUA. In addition, cortisol potentiated the NE-induced increase in Ca2+concentration in PUA, but increased NE-mediated contraction for a given amount of Ca2+ concentration in NUA. Collectively, the results indicate that cortisol potentiates NE-mediated contractions differentially in NUA and PUA, i.e., by upregulating α1-adrenoceptor density leading to increased Ca2+ mobilization in PUA while increasing α1-adrenoceptor coupling efficiency and myofilament Ca2+ sensitivity in NUA. In addition, the results suggest that pregnancy increases type 2 11β-hydroxysteroid dehydrogenase activity in the UA.

Effects of maturation and acute hypoxia on receptor-IP3 coupling in ovine common carotid arteries

Whereas previous studies have established that many mechanisms mediating pharmacomechanical coupling are subject to regulation, evidence of physiological regulation of the coupling efficiency between receptor activation and second-messenger production is scarce. The present studies address the hypothesis that acute hypoxia and maturation can influence the mass of second-messenger production for each activated agonist-bound receptor (“receptor gain”). For this assessment, receptor density and agonist affinity values were used to calculate 5-hydroxytryptamine (5-HT) concentrations that would produce standardized numbers of bound receptors (8.5 fmol/mg protein) in each experimental group and thus minimize effects of age or hypoxia on receptor density or agonist affinity. After 3 min of exposure to these 5-HT concentrations, normoxic magnitudes of contraction were similar (as %potassium maxima) in fetal (50 ± 14%) and adult (40 ± 9%) arteries, but hypoxia (Po 2 ≈ 9–12 Torr for 30 min) depressed contractile tensions with a significantly different time course and magnitude in fetal (30 ± 10%) and adult (17 ± 11%) arteries ( P < 0.05). Basal inositol 1,4,5-trisphosphate (IP3) values (in pmol/mg protein) were significantly greater in fetal (94 ± 16) than in adult (44 ± 6) arteries, and integrated areas above baseline for the IP3 time courses (in nmol-s/mg protein) were significantly greater in fetal than in adult arteries both in normoxic (14.3 ± 1.8 vs. 9.1 ± 1.6) and hypoxic (15.0 ± 2.1 vs. 8.6 ± 1.2) conditions ( P < 0.05). Hypoxia altered the IP3 time courses both in the fetus and the adult but had no significant effect on IP3 mobilization or receptor gain. These data demonstrate that for the 5-HT2areceptor predominant in this preparation, receptor gain can be experimentally determined, is not influenced by acute hypoxia, but is greater in fetal than in adult ovine carotid arteries.