Intracellular calcium responses and shape conversions induced by endothelin in cultured subepithelial fibroblasts of rat duodenal villi

Abstract

Subepithelial fibroblasts of rat duodenal villi were cultured and the physiological characteristics were studied using fura-2 fluorescence. The intracellular calcium concentration (Ca ²⁺_i ) responded to various substances, i.e., endothelins (ET1 and ET3), substance P, serotonin, angiotensin II, ATP, and bradykinin. The Ca ²⁺_i responses to ET1 (>0.1 nM) and ET3 (>1 nM) were transient and sometimes followed oscillations that consisted of an initial Ca²⁺ release from the intracellular store and a sustained Ca²⁺ influx. Simultaneously with Ca ²⁺_i measurement, changes in the cell shape were monitored using fluorescence intensity upon 360-nm excitation. Stellate cells (with thick cell body and slender processes), formed as a result of 1 mM dibutyryl(Bt₂)-cAMP treatment, began to change immediately after the short-term application of the endothelin and became flat about 20 min later. This process was not affected by the depletion of extracellular Ca²⁺ or by the treatment with BAPTA acetoxymethyl ester that completely suppressed the Ca ²⁺_i response. Substance P (>100 nM) increased Ca ²⁺_i , but did not induce any morphological changes. The conversion of the shape from flat to stellate, induced by Bt₂cAMP treatment, was not accompanied by any Ca ²⁺_i change. BQ-123, a specific blocker of the ET_A-type receptor, did not block either Ca ²⁺_i change or shape conversion at low (100 nM) concentration. The results indicated that shape conversion in subepithelial fibroblasts did not require any Ca ²⁺_i response. Our findings regarding the characteristics of subepithelial fibroblasts in intestinal villi imply a functional similarity to astrocytes in the brain.