title: Lamellipod extension and K+ current in osteoclasts are regulated by different types of G proteins.
abstract: Osteoclasts are the cells responsible for the resorption of bone and other mineralized tissues. GTP-binding proteins (G proteins) play important roles in regulating the activity of many cell types; however, there is limited knowledge of their functions in osteoclasts. We used the patch-clamp technique in the whole-cell configuration to introduce either hydrolysis-resistant guanosine triphosphate analogues or fluoroaluminate into single rat osteoclasts, and examined the effects of G protein activation on cell morphology and ionic conductances. Guanosine 5'-O-(3-thiotriphosphate) or 5'-guanylyl-imidodiphosphate, but not the control compounds adenosine 5'-O-(3-thiotriphosphate) or guanosine 5'-O-(2-thiodiphosphate), induced: (1) prompt spreading due to extension of lamellipodia; and (2) after a latency of several minutes, complete suppression of the inwardly rectifying K+ current. Pertussis toxin did not alter either spreading or suppression of K+ current induced by guanosine 5'-O-(3-thiotriphosphate). Cytochalasin D, but not colchicine, prevented guanosine 5'-O-(3-thiotriphosphate)-induced spreading, consistent with actin polymerization underlying lamellipod extension. Whole-cell capacitance did not change during guanosine 5'-O-(3-thiotriphosphate)-induced spreading, which is consistent with a lack of change in total plasma membrane area. Fluoroaluminate did not induce spreading, but it did suppress the K+ current. The differential effects of fluoroaluminate and guanosine 5'-O-(3-thiotriphosphate) suggest that lamellipod extension is regulated by a small molecular mass, monomeric G protein, whereas the inwardly rectifying K+ current is regulated by a large molecular mass, heterotrimeric G protein. Thus, osteoclast motility and ion transport are regulated by separate G protein-coupled pathways.
authors.affiliation: Department of Physiology, University of Western Ontario, London, Canada.
authors.forename: S A
authors.initials: SA
authors.lastname: Arkett
authors.forename: S J
authors.initials: SJ
authors.lastname: Dixon
authors.forename: S M
authors.initials: SM
authors.lastname: Sims
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001862:Bone Resorption / Q000503:physiopathology; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D003078:Colchicine / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D037342:Pertussis Toxin; D011188:Potassium / Q000378:metabolism*; D011554:Pseudopodia / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D000199:Actins; D010566:Virulence Factors, Bordetella; D015638:Cytochalasin D; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D011188:Potassium; D003078:Colchicine