Perez JF, Sanderson MJ. The contraction of smooth muscle cells of intrapulmonary arterioles is determined by the frequency of Ca2+ oscillations induced by 5-HT and KCl.
ACTA ACUST UNITED AC 2005;
125:555-67. [PMID:
15928402 PMCID:
PMC2234075 DOI:
10.1085/jgp.200409217]
[Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Increased resistance of the small blood vessels within the lungs is associated with pulmonary hypertension and results from a decrease in size induced by the contraction of their smooth muscle cells (SMCs). To study the mechanisms that regulate the contraction of intrapulmonary arteriole SMCs, the contractile and Ca(2+) responses of the arteriole SMCs to 5-hydroxytrypamine (5-HT) and KCl were observed with phase-contrast and scanning confocal microscopy in thin lung slices cut from mouse lungs stiffened with agarose and gelatin. 5-HT induced a concentration-dependent contraction of the arterioles. Increasing concentrations of extracellular KCl induced transient contractions in the SMCs and a reduction in the arteriole luminal size. 5-HT induced oscillations in [Ca(2+)](i) within the SMCs, and the frequency of these Ca(2+) oscillations was dependent on the agonist concentration and correlated with the extent of sustained arteriole contraction. By contrast, KCl induced Ca(2+) oscillations that occurred with low frequencies and were preceded by small, localized transient Ca(2+) events. The 5-HT-induced Ca(2+) oscillations and contractions occurred in the absence of extracellular Ca(2+) and were resistant to Ni(2+) and nifedipine but were abolished by caffeine. KCl-induced Ca(2+) oscillations and contractions were abolished by the absence of extracellular Ca(2+) and the presence of Ni(2+), nifedipine, and caffeine. Arteriole contraction was induced or abolished by a 5-HT(2)-specific agonist or antagonist, respectively. These results indicate that 5-HT, acting via 5-HT(2) receptors, induces arteriole contraction by initiating Ca(2+) oscillations and that KCl induces contraction via Ca(2+) transients resulting from the overfilling of internal Ca(2+) stores. We hypothesize that the magnitude of the sustained intrapulmonary SMC contraction is determined by the frequency of Ca(2+) oscillations and also by the relaxation rate of the SMC.
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