A PERTUSSIS TOXIN-SENSITIVE GTP-BINDING PROTEIN COUPLES ENDOTHELIN TO PHOSPHOLIPASE-C IN RAT MESANGIAL CELLS

The mechanisms of stimulation of phospholipase C (PLC) by endothelin, specifically the role of guanine nucleotide-binding proteins (GTP-binding proteins) in coupling the endothelin receptor to PLC, were investigated in rat mesangial cells. Endothelin-1 (ET) synergistically released inositol polyphosphates in the presence of the stimulatory GTP analogue guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S) in permeabilized cells. In addition, in intact cells, pertussis toxin partially inhibited the stimulation of total inositol phosphates (IP(n)) by ET. Pertussis toxin also reduced the peak ET-stimulated intracellular free calcium level ([Ca2+]i) in these cells, both in the presence and absence of extracellular calcium. Pertussis toxin induced ADP ribosylation of a 41- to 43-kDa protein in mesangial cell membranes, and this effect was inhibited by prior exposure to ET and augmented by the inhibitory GDP analogue, guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S). Thus a pertussis toxin-sensitive GTP-binding protein is involved in the activation of PLC by ET in glomerular mesangial cells.