Characteristics of Ca2 Transients

Using microspectrofluorimetry to measure the [Ca2+]; in single cells, studies from our laboratory and others have revealed that agonists controlling smooth muscle tone via activation of seven transmembrane domain, G-coupled surface membrane receptors (e.g., angiotensin II, endothelin-1, extracellular ATP and UTP, noradrenaline, and serotonin) induce a complex temporal [Ca2+]| response in PASMCs. The pattern of the response depends on several factors, including the type of arteries (proximal vs distal), the species, the phenotype of the cells (i.e., fresh vs. cultured cells) and the agonist considered. For example, in short term cultured (24-48 h) vascular myocytes from intrapulmonary arteries (300500 (¿m o.d.), endothelin-1 induces a transient increase in [Ca2+]( followed by a small plateau. The amplitude of the peak is dependent on the endothelin-1 concentration from 0.1 to 10 nM (44). In freshly isolated and cultured myocytes fromproximal extrapulmonary and intralobar arteries, the agonist-induced [Ca2+]| response is composed of a series of cyclic increases in [Ca2+]i, so-called Ca2+ oscillations. The [Ca2+]j rises, after a delay of 5 to 10 sec, from a resting value of 60-70 nM to a peak value of 400-800 nM (20, 25) before decreasing once again. This first increase is transient and followed by successive peaks of constant duration (Fig. 1). The oscillation frequency varies from 4-6 to 25-30/min, according to the cell type and the agonist concentration. On average, 5080% of cells exhibit [Ca2+]j oscillation under identical experimental conditions.

The concentration of agonist is the main factor that modulates the pattern of Ca2+ oscillations. However, this modulation still depends on both type of tissue and the nature of the agonist considered. In some cases (cultured canine PASMCs), both amplitude and the frequency of the Ca2+ oscillations increase with the mediator concentration (22). In some others cases (freshly isolated rat PASMCs), the overall pattern of oscillations appears to be independent of the mediator concentration, but the percentage of cells exhibiting Ca2+ oscillations in response to mediator stimulation does depend on the mediator concentration (20, 25). In this latter case, the combination of the number of responding cells with the amplitude of the first [Ca2+]: peak also reveals a relationship between the concentration of the mediator and the [Ca2+], response (25).

In contrast to mediators acting at cell surface membrane receptors, caffeine and ryanodine, known to act directly on the SR and to potentiate Ca2+-induced Ca2+release, always induce a transient or monotonic increase of [Ca2+], (Fig. 3C) that is never followed by oscillations in PASMCs (18, 25, 27). The amplitude of this transient [Ca2+]j -response is dependent on the concentration of caffeine used (0.1-10 mM).

Figure 1. Agonist-induced Ca2+ oscillations in freshly isolated PASMCs from the rat main pulmonary artery. Short (30 s) ejection of angiotensin II (A, Ang II, 0.1 nM) or endothelin-1 (B and C, ET-1,0.01 nM) near the cell induced oscillations in [Ca2*],, These Ca2+ oscillations were not altered when PASMCs were superfused with a Ca2+-free physiological salt solution (PSS, A) but, disappeared when PASMCs are superfused for 15 min with 1 pM thapsigargin (TG, B). When PASMCs were superfused for 10 min with 1 nM of 2-APB, the ET-l-induced [Ca2+]j oscillations disappeared (C). In each panel, the first record (left trace) is the control response. Each trace was recorded from a different cell and is typical of 8-10 cells.

Figure 1. Agonist-induced Ca2+ oscillations in freshly isolated PASMCs from the rat main pulmonary artery. Short (30 s) ejection of angiotensin II (A, Ang II, 0.1 nM) or endothelin-1 (B and C, ET-1,0.01 nM) near the cell induced oscillations in [Ca2*],, These Ca2+ oscillations were not altered when PASMCs were superfused with a Ca2+-free physiological salt solution (PSS, A) but, disappeared when PASMCs are superfused for 15 min with 1 pM thapsigargin (TG, B). When PASMCs were superfused for 10 min with 1 nM of 2-APB, the ET-l-induced [Ca2+]j oscillations disappeared (C). In each panel, the first record (left trace) is the control response. Each trace was recorded from a different cell and is typical of 8-10 cells.

Was this article helpful?

0 0
Reducing Blood Pressure Naturally

Reducing Blood Pressure Naturally

Do You Suffer From High Blood Pressure? Do You Feel Like This Silent Killer Might Be Stalking You? Have you been diagnosed or pre-hypertension and hypertension? Then JOIN THE CROWD Nearly 1 in 3 adults in the United States suffer from High Blood Pressure and only 1 in 3 adults are actually aware that they have it.

Get My Free Ebook


Post a comment