Anti-idiotypic antibodies to delineate epitope specificity of anti-amiloride antibodies

Sympathetic neural control of integrated cardiovascular function: Insights from measurement of human sympathetic nerve activity

Sympathetic neural control of cardiovascular function is essential for normal regulation of blood pressure and tissue perfusion. In the present review we discuss sympathetic neural mechanisms in human cardiovascular physiology and pathophysiology, with a focus on evidence from direct recordings of sympathetic nerve activity using microneurography. Measurements of sympathetic nerve activity to skeletal muscle have provided extensive information regarding reflex control of blood pressure and blood flow in conditions ranging from rest to postural changes, exercise, and mental stress in populations ranging from healthy controls to patients with hypertension and heart failure. Measurements of skin sympathetic nerve activity have also provided important insights into neural control, but are often more difficult to interpret since the activity contains several types of nerve impulses with different functions. Although most studies have focused on group mean differences, we provide evidence that individual variability in sympathetic nerve activity is important to the ultimate understanding of these integrated physiological mechanisms.

Noninvasive evaluation of cardiac output during postural change and exercise in humans: comparison between the modelflow and pulse dye-densitometry

To investigate whether the Model-flow method, by simulating the aortic input impedance model from a noninvasive monitoring of arterial blood pressure, reflected a reliable measure of cardiac output (CO) during postural change and whole-body exercise occurring in daily life, we compared the Modelflow-estimated CO with a simultaneous reference determined by the pulse dye-densitometry. Nine healthy volunteers performed postural change from supine to upright and dynamic stepping exercise. The Modelflow-estimated CO decreased to 4.8 +/- 0.5 l/min, from 5.8 +/- 0.6 l/min, during the postural change and increased to 12.8 +/- 1.3 l/min during a stepping exercise, returning to 5.1 +/- 0.4 l/min at 5 min after exercise. When comparing the pooled data of CO during resting and following exercise between the Modelflow and pulse dye-densitometry, we found that the average CO did not differ between the two estimates and that there was a significant correlation between them; the slope of the linear regression line corresponded to approximately 1.0. Although such linear relationship was also observed in an individual subject, the slope of the regression line varied from 0.737 to 1.588 among the subjects. The calibration of the Modelflow-estimated CO with the dye-densitometry value at supine or upright improved a correlation between the two estimates. Thus it is likely that the noninvasive Modelflow simulation from arterial blood pressure can provide a reliable estimation of group-average cardiac output during postural change and stepping exercise occurring in daily life. It will be recommended for a more accurate estimation of cardiac output in a given subject to calibrate the Modelflow data with an independent measure.

Reflex responses in plasma catecholamines caused by static contraction of skeletal muscle

To examine a hypothesis of whether static muscle contraction produces a release of catecholamines from the adrenal medulla via reflex stimulation of preganglionic adrenal sympathetic nerve activity induced by receptors in the contracting muscle, we compared the reflex responses in a concentration of epinephrine (Ep) and norepinephrine (NEp) in arterial plasma during static contraction and during a mechanical stretch of the hindlimb triceps surae muscle in anesthetized cats. Static contraction was evoked by electrically stimulating the peripheral ends of the cut L(7) and S(1) ventral roots at 20 or 40 Hz. Mean arterial pressure (MAP) and heart rate (HR) increased 23 +/- 3.1 mmHg and 19 +/- 4.3 beats/min during static contraction. Ep in arterial plasma increased 0.18 +/- 0.072 ng/ml over the control of 0.14 +/- 0.051 ng/ml within 1 min from the onset of static contraction, and NEp increased 0.47 +/- 0.087 ng/ml over the control of 0.71 +/- 0.108 ng/ml. Following a neuromuscular blockade, although the same ventral root stimulation failed to produce the cardiovascular and plasma catecholamine responses, the mechanical stretch of the muscle increased MAP, HR, and plasma Ep, but not plasma NEp. With bilateral adrenalectomy, the baseline Ep became negligible (0.012 +/- 0.001 ng/ml) and the baseline NEp was lowered to 0.52 +/- 0.109 ng/ml. Neither static contraction nor mechanical stretch produced significant responses in plasma Ep and NEp following the adrenalectomy. These results suggest that static muscle contraction augments preganglionic adrenal sympathetic nerve activity, which in turn secretes epinephrine from the adrenal medulla into plasma. A muscle mechanoreflex from the contracting muscle may play a role in stimulation of the adrenal sympathetic nerve activity.

Differential expression of RNA and protein of the three pore-forming subunits of the amiloride-sensitive epithelial sodium channel in taste buds of the rat

Salt taste signals from the rat anterior tongue are probably transduced via epithelial sodium channels (ENaCs) residing in the apical cellular pole of taste cells. The signals are blocked by mucosal amiloride in low microM concentrations. In contrast, the rat vallate papilla does not contribute to amiloride-blockable salt taste. Two approaches were used to probe for the three subunits of ENaC in the anterior and posterior tongue of the rats in sodium balance. (a) Immunohistochemistry with antibodies against ENaC subunits and against amiloride binding sites. In the anterior tongue, reactivity for alpha-, beta-, and gamma-subunits was present in taste buds and lingual epithelium. In the posterior tongue vallate papilla, reactivity for alpha-subunit and for amiloride binding sites was easily demonstrable, whereas that for beta-subunit and especially for gamma-subunit was weaker than in the anterior tongue. (b) RT-PCR techniques were used to probe for the presence of ENaC subunit mRNA. In isolated taste buds of the anterior tongue, mRNA of all three subunits was found, whereas in isolated taste buds of the vallate papilla only mRNA of the alpha-subunit was easily detectable. That of beta- and gamma-subunits was much less abundant. RNA of all three subunits was abundant only in taste buds of the anterior tongue. Therefore, subsets of elongated taste cells do express ENaC, but regional differences exist in the transcription and expression of subunits. The regional differences suggest that amiloride-sensitive salt taste, which requires all three subunits, is present in the anterior but not the posterior tongue of rats, as functional studies indicate.

Occurrence of ENaC subunit mRNA and immunocytochemistry of the channel subunits in taste buds of the rat vallate papilla

Epithelial Na+ channels (ENaCs) are thought to mediate the amiloride-blockable salt taste. The rat vallate papilla does not contribute to amiloride-blockable salt taste, yet the presence of ENaC-mRNA in this tissue has been reported. Is ENaC actually contained in the taste cells, or is it merely present in the supporting lingual epithelium? To avoid contamination by ENaC contained in the lingual epithelium, we physically isolated taste buds from the vallate papilla and used mRNA purification followed by reverse transcriptase polymerase chain reaction (RT-PCR) to investigate the presence of ENaC-type message in the isolated buds. mRNA of alpha-, beta- and gamma-subunits was detected, the alpha-signal being the strongest. These results provide first molecular evidence for the presence of ENaC subunits in taste buds that were isolated from the posterior tongue and were free of epithelial contamination. In addition, we used immunohistochemistry to show ENaC-like reactivity in posterior tongue taste cells. Interestingly, the immunoreactivity was not predominantly apical but was intracellular and close to or at the basolateral membrane. The function of basolateral ENaC-type channels is unknown. Possibly, the channels are normally closed or of very low open probability in the resting state.

Heart rate control during exercise by baroreceptors and skeletal muscle afferents

The objective of this brief review is to discuss current hypotheses describing the roles of the arterial baroreflex and reflexes originating from afferents within the active skeletal muscle (metaboreceptors and mechanoreceptors) in mediating reflex changes in heart rate. The major focus is on how the techniques of reflex activation and analysis of the subsequent responses may markedly affect conclusions drawn regarding the role of these reflexes during exercise. The disparate conclusions regarding the importance of these reflexes are likely reflective of the different autonomic mechanisms mediating the reflex responses (i.e., parasympathetic vs sympathetic) as well as the techniques utilized for reflex activation and analysis. Conclusions reached are that these reflexes are important in the regulation of heart rate during exercise but the relative roles are dependent on work load.