Alpha-adrenoceptor regulation of inositol phosphates, internal calcium and membrane current in DDT1 MF-2 smooth muscle cells.
The effect of alpha 1-adrenoceptor stimulation on inositol phosphates (InsPs), intracellular Ca2+ and membrane current was measured in vas deferens DDT1 MF-2 cells. The InsPs were analyzed after labelling the cells with [3H]myo-inositol using high performance liquid chromatography and the internal Ca2+ concentration was determined by measuring fluorescence using Indo-1 as probe. Noradrenaline stimulated the formation of inositol mono-, bis-, tris- and tetrakisphosphate (InsP, InsP2, InsP3 and InsP1) concentration-dependently in the presence of LiCl, but no changes occurred in the formation of inositol pentakis- and hexakisphosphate (InsP5 and InsP6). Various isomers of InsP3 and InsP4 were detected after noradrenaline (10(-5) M) stimulation (without LiCl). Only the formation of the putative second messenger Ins(1,4,5)P3 formation was increased in the presence of noradrenaline. The internal Ca2+ concentration was enhanced both in the presence and absence of external Ca2+ upon addition of noradrenaline. The response in the presence of extracellular Ca2+ was not affected by diltiazem (10(-5) M). The increase in cytoplasmic Ca2+ could be repeatedly evoked, but could be elicited only once under Ca2(+)-free conditions. The relation between the noradrenaline concentration and the rise in internal Ca2+ was similar to that obtained for the InsP formation. Half-maximal effects were obtained at about 1 microM. The membrane current measured in these cells by using the whole-cell patch-clamp method was not changed by the agonist (10(-5) M). These results suggest that noradrenaline acts on DDT1 MF-2 smooth muscle cells, represented by the formation of InsP3 and enhancement of internal Ca2+ originating from internal structures, via the alpha 1B-adrenoceptor subtype.
Nelemans
A
A
Department of Pharmacology/Clinical Pharmacology, University of Groningen, The Netherlands.
Hoiting
B
B
Molleman
A
A
Duin
M
M
den Hertog
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D007295:Inositol Phosphates / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D009638:Norepinephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D014649:Vas Deferens / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure
D007295:Inositol Phosphates; D011942:Receptors, Adrenergic, alpha; D002118:Calcium; D009638:Norepinephrine