Cited 4 times since 1995 (0.1 per year) source: EuropePMC Cell calcium, Volume 18, Issue 6, 1 1 1995, Pages 515-525 Alpha-adrenergic agonist and endothelin-1 induced intracellular Ca2+ response in the presence of a Ca2+ entry blocker in cultured rat ventricular myocytes. De Jonge HW, Atsma DE, van der Valk-Kokshoorn EJ, van Heugten HA, van der Laarse A, Lamers JM
Previously we demonstrated that stimulation of cultured neonatal rat ventricular myocytes by either alpha 1-adrenergic agonist or endothelin-1 resulted in a rapid formation of total inositolphosphates, although the levels of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate did not rise significantly. The aim of this study was to examine whether stimulation by alpha 1-adrenergic agonist and endothelin-1 could still elicit phosphatidylinositol cycle mediated intracellular Ca2+ mobilization in these cells. The intracellular free Ca2+ concentration ([Ca2+]i) was measured by single cell imaging dual wavelength fluorescence microscopy in Fura-2-loaded cardiomyocytes. The interference of agonist induced [Ca2+]i responses by the beat to beat variation of [Ca2+]i was prevented by arresting the cells with the Ca2+ entry blocker diltiazem (10 microM). The [Ca2+]i response (expressed as % of baseline ratio of fluorescence intensities of Fura-2 at 340 nm and 380 nm excitation wavelength), induced by phenylephrine (10(-4) M) and endothelin-1 (10(-8) M) was small, up to 20% of baseline after 9-20 min. In contrast, Ca(2+)-influx induced by incubation in Na(+)-free buffer caused a steep increase of [Ca2+]i up to 150% of baseline after 30 s. Analysis of single cells following stimulation with phenylephrine or endothelin-1 showed heterogeneity with respect to a rise in [Ca2+]i. However, if rapid Ca(2+)-influx was induced by incubation in Na(+)-free buffer, [Ca2+]i responses in individual myocytes occurred homogeneously. It is concluded that the alpha 1-adrenergic agonist and endothelin-1 induced [Ca2+]i responses are delayed in time, small and quite heterogeneous among cells. The findings are in agreement with earlier observations which revealed no detectable overall increase of the Ca2+ releasing inositolphosphates under these conditions and suggest that other second messengers, such as 1,2-diacylglycerol, are involved in the agonist mediated Ca2+ signals.
