Endothelin-induced contraction of bronchiole and pulmonary arteriole smooth muscle cells is regulated by intracellular Ca2+ oscillations and Ca2+ sensitization

Abstract

Endothelin-1 (ET) induces increases in intracellular Ca2+ concentration ([Ca2+]i), Ca2+ sensitization, and contraction of both bronchiole and pulmonary arteriole smooth muscle cells (SMCs) and may play an important role in the pathophysiology of asthma and pulmonary hypertension. However, because it remains unclear how changes in [Ca2+]i and the Ca2+ sensitivity regulate SMC contraction, we have studied mouse lung slices with phase-contrast and confocal microscopy to correlate the ET-induced contraction with the changes in [Ca2+]i and Ca2+ sensitivity of bronchiole and arteriole SMCs. In comparison with acetylcholine (ACh) or serotonin (5-HT), ET induced a stronger and long-lasting contraction of both bronchioles and arterioles. This ET-induced contraction was associated with prominent asynchronous Ca2+ oscillations that were propagated as Ca2+ waves along the SMCs. These Ca2+ oscillations were mediated by cyclic intracellular Ca2+ release and required external Ca2+ for their maintenance. Importantly, as the frequency of the Ca2+ oscillations increased, the extent of contraction increased. ET-induced contraction was also associated with an increase in Ca2+ sensitivity. In “model” slices in which the [Ca2+]i was constantly maintained at an elevated level by pretreatment of slices with caffeine and ryanodine, the addition of ET increased bronchiole and arteriole contraction. These results indicate that ET-induced contraction of bronchiole and arteriole SMCs is regulated by the frequency of Ca2+ oscillations and by increasing the sensitivity of the contractile machinery to Ca2+.