The contribution of Ca²⁺ signaling and Ca²⁺ sensitivity to the regulation of airway smooth muscle contraction is different in rats and mice

Abstract

Bai Y, Sanderson MJ. The contribution of Ca 2ϩ signaling and Ca 2ϩ sensitivity to the regulation of airway smooth muscle contraction is different in rats and mice. Am J Physiol Lung Cell Mol Physiol 296: L947-L958, 2009. First published April 3, 2009 doi:10.1152/ajplung.90288.2008.-To determine the relative contributions of Ca 2ϩ signaling and Ca 2ϩ sensitivity to the contractility of airway smooth muscle cells (SMCs), we compared the contractile responses of mouse and rat airways with the lung slice technique. Airway contraction was measured by monitoring changes in airway lumen area with phase-contrast microscopy, whereas changes in intracellular calcium concentration ([Ca 2ϩ ]i) of the SMCs were recorded with laser scanning microscopy. In mice and rats, methacholine (MCh) or serotonin induced concentration-dependent airway contraction and Ca 2ϩ oscillations in the SMCs. However, rat airways demonstrated greater contraction compared with mice, in response to agonist-induced Ca 2ϩ oscillations of a similar frequency. Because this indicates that rat airway SMCs have a higher Ca 2ϩ sensitivity compared with mice, we examined Ca 2ϩ sensitivity with Ca 2ϩ -permeabilized airway SMCs in which the [Ca 2ϩ ]i was experimentally controlled. In the absence of agonists, high [Ca 2ϩ ]i induced a sustained contraction in rat airways but only a transient contraction in mouse airways. This sustained contraction of rat airways was relaxed by Y-23672, a Rho kinase inhibitor, but not affected by GF-109203X, a PKC inhibitor. The subsequent exposure of Ca 2ϩ -permeabilized airway SMCs, with high [Ca 2ϩ ]i, to MCh elicited a further contraction of rat airways and initiated a sustained contraction of mouse airways, without changing the [Ca 2ϩ ]i of the SMCs. Collectively, these results indicate that airway SMCs of rats have a substantially higher innate Ca 2ϩ sensitivity than mice and that this strongly influences the transduction of the frequency of Ca 2ϩ oscillations into the contractility of airway SMCs. lung slices; Ca 2ϩ oscillations; confocal microscopy; asthma; hyperresponsiveness ASTHMA IS CHARACTERIZED BY airway inflammation and airway hyperresponsiveness to nonspecific stimulation. Although airway inflammation is known to result in airway remodeling, airway hyperresponsiveness occurs in the early stages of asthma when no obvious airway remodeling is discernable. Consequently, the fundamental mechanism leading to the excessive contraction of airway smooth muscle cells (SMCs) remains unknown. A straightforward hypothesis is that the innate contractility of the SMCs has been enhanced in asthmatic airways. However, the experimental evidence addressing the contractile responses of asthmatic SMCs in vitro is inconsistent. Increased (4, 6, 18, 21), normal (4, 5, 10, 34), and even reduced (12, 33, 37) airway constriction has been reported in human asthmatic or animal airways. These discrepancies may also result from the different protocols, methods, and parameters used to evaluate SMCs contraction.To determine whether the cont...

Human Airway Contraction and Formoterol-Induced Relaxation Is Determined by Ca2+ Oscillations and Ca2+ Sensitivity

“…For example, human airways respond to histamine, whereas mouse airways only respond very weakly to histamine concentrations of 10 mM or greater. On the other hand, human airways do not contract in response to 5HT, which is a potent bronchoconstrictor in mice and rats (9,12,28). The frequency of the Ca 21 oscillations induced by the same concentration of agonist varies from 5 to 20 peaks per minute in these three species.…”

“…It was clear that the specific responses of the SMCs from different species, as well as different airway locations, were different (9,27). For example, human airways respond to histamine, whereas mouse airways only respond very weakly to histamine concentrations of 10 mM or greater.…”

“…From studies with animals, it has been shown that agonist-induced increases in [Ca 21 ] i occur in the form of oscillatory Ca 21 waves rather than just a static increase in [Ca 21 ] i (5)(6)(7)(8). Although the frequency of these Ca 21 oscillations has been found to increase with agonist concentration, and that this correlates with increased contraction, the frequency of the Ca 21 oscillations generated by similar agonist concentrations differs considerably between species (9).…”

“…Our previous studies with Ca 21 -permeabilized mouse lung slices have shown that airway and vascular SMCs express different levels of Ca 21 sensitivity (10), and this has the result that the same stimulus generates different amounts of contraction. Similarly, airway SMCs from different species display different magnitudes of contraction in response to similar changes in [Ca 21 ] i (9).…”

Acción de la simvastatina en la contracción de músculo liso de anillo traqueal inducida por estímulo químico y térmico

“…Para la contracción del músculo liso se requiere la presencia de Ca +2 procedente de reservorios intracelulares, pero también se sabe que estos iones provienen desde el exterior de la célula a través de la membrana de la misma [10]. Estos canales de calcio están ubicados en sitios específicos de la membrana que son ricos en colesterol y se ha demostrado en músculo liso vascular que la simvastatina inhibe la formación del colesterol endógeno y afectan la "Rafts" lipídica, comprometiendo de esta manera las proteínas que conforman los canales de Ca 2+ de la membrana celular y los procesos de señalización que permiten tardíamente la apertura de canales de Ca 2+ en el sarcolema [11].…”