Journal of Cell Science, Vol 107, Issue 2 517-526, Copyright © 1994 by Company of Biologists

JOURNAL ARTICLES

Lamellipod extension and K+ current in osteoclasts are regulated by different types of G proteins

SA Arkett, SJ Dixon and SM Sims
Department of Physiology, University of Western Ontario, London, Canada.

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.
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